The Ice Cream eBook

Ice cream has a long history as a popular dairy food item. It has evolved from a manually manufactured household product to a very automated industrial product.

This is the Ice Cream Book, a subset of the Dairy Education Series. If you have come to this page directly, then you can go back to the beginning to start learning about dairy science and technology and dairy products.

This site was developed and is continually maintained by:   

Professor H. Douglas Goff
University of Guelph
Canada

I hope you find this site useful as a reference, or for teaching or training purposes. If you do use information from this site, please cite your source as Professor H. Douglas Goff, Dairy Science and Technology Education Series, University of Guelph, Canada.

Reproduction of this site, or any portions thereof, in either print or electronic form without permission of the author is strictly prohibited.

This section on ice cream is fairly extensive and covers all the following topics:

Ice Cream History and Folklore

Most of the following material has been extracted from "The History of Ice Cream", written by the International Association of Ice Cream Manufacturers (IAICM), Washington DC, 1978, now IDFA. As you will note below, however, much of the early history of ice cream remains unproven folklore.

"Once upon a time, hundreds of years ago, Charles I of England hosted a sumptuous state banquet for many of his friends and family. The meal, consisting of many delicacies of the day, had been simply superb but the "coup de grace" was yet to come. After much preparation, the King's french chef had concocted an apparently new dish. It was cold and resembled fresh- fallen snow but was much creamier and sweeter than any other after- dinner dessert. The guests were delighted, as was Charles, who summoned the cook and asked him not to divulge the recipe for his frozen cream. The King wanted the delicacy to be served only at the Royal table and offered the cook 500 pounds a year to keep it that way. Sometime later, however, poor Charles fell into disfavour with his people and was beheaded in 1649. But by that time, the secret of the frozen cream remained a secret no more. The cook, named DeMirco, had not kept his promise."

"This story is just one of many of the fascinating tales which surround the evolution of our country's most popular dessert, ice cream. It is likely that ice cream was not invented, but rather came to be over years of similar efforts. Indeed, the Roman Emperor Nero Claudius Caesar is said to have sent slaves to the mountains to bring snow and ice to cool and freeze the fruit drinks he was so fond of. Centuries later, the Italian Marco Polo returned from his famous journey to the Far East with a recipe for making water ices resembling modern day sherbets."

A newly published book, by Caroline Liddell and Robin Weir, Ices: The Definitive Guide, publ. by Hodder and Stoughton, 1993, ISBN 0-340-58335-5, suggests that the historical basis of these tales is skeptical.

What follows is from the opening of the first chapter of their book:

Most books are full of myths about the history of ice cream. According to popular accounts, Marco Polo (1254-1324) saw ice creams being made during his trip to China, and on his return, introduced them to Italy. The myth continues with the Italian chefs of the you Catherine de'Medici taking this magical dish to France when she went there in 1533 to marry the Duc d'Orleans, with Charles I rewarding his own ice-cream maker with a lifetime pension on condition that he did not divulge his secret recipe to anyone, thereby keeping ice cream as a royal prerogative.

Unfortunately, there is no historical evidence to support any of these stories. They would appear to be purely the creation of imaginative nineteenth-century ice-cream makers and vendors. Indeed, we have found no mention of any of these stories before the nineteenth century.

They go on to refute the claims about Marco Polo, Catherine de'Medici, and Charles I (in particular, while the IAICM reference credits DeMirco as the Charles I chef, apparently while other various sources credit 10 different men, there are no records of such a pension being paid to any of Charles I's cooks).

They do go on in their book to discuss history for which there is a record, with (I think) the earliest written record being something made in China.

Chris Clarke, in his 2004 Royal Society of Chemistry monograph "The Science of Ice Cream", points out quite correctly that the history of ice cream is closely associated with the development of refrigeration techniques and can thus be traced in several stages:

  1. Cooling food and rink by mixing it with snow or ice;
  2. The discovery that dissolving salts in water produces cooling;
  3. The discovery (and spread of knowledge) that mixing salts and snow or ice cools even further - mid to late 17th century - the inclusion of cream in the water ices also evolved around this time;
  4. The invention of the ice cream maker in the mid 19th century;
  5. The development of mechanical refrigeration in the later 19th and early 20th centuries - which led to the development of the modern ice cream industry.

Back to the IAICM history....

"In 1774, a caterer named Phillip Lenzi announced in a New York newspaper that he had just arrived from London and would be offering for sale various confections, including ice cream.* Dolley Madison, wife of U.S. President James Madison, served ice cream at her husband's Inaugural Ball in 1813.**

"The first improvement in the manufacture of ice cream (from the handmade way in a large bowl) was given to us by a New Jersey woman, Nancy Johnson, who in 1846 invented the hand-cranked freezer. This device is still familiar to many. By turning the freezer handle, they agitated a container of ice cream mix in a bed of salt and ice until the mix was frozen. Because Nancy Johnson lacked the foresight to have her invention patented, her name does not appear on the patent records.* A similar type of freezer was, however, patented on May 30, 1848, by a Mr. Young who at least had the courtesy to call it the "Johnson Patent Ice Cream Freezer".

*This, however, is not true. On Sep 9, 1843, the US Patent Office issued patent No. 3254 to Mrs. Johnson. The freezer consisted of a tub, a cylinder with close-fitting lid, and a removable dasher. William Young received the 2nd patent and claimed his was an improvement over Johnson's, as both the cylinder and dasher revolved, agitating the ice cream more completely.

"Commercial production was begun in North America in Baltimore, Maryland, 1851, by Mr. Jacob Fussell, now known as the father of the American ice cream industry."

*Readex has published the digital Early American Newspapers, which shows that this advertisement appeared in November 1773:
Paper: Rivington's New-York Gazetteer; Date: 1773-11-25; Iss: 32; Page: [4];

**For a biography of Dolley Madison at the Montpelier, VA site, see Montpelier's Dolley Madison's Bio. An unsubstantiated (by me) story passed on to me regarding Dolley's discovery of ice cream goes like this: "Betty Jackson, a black woman from Chadds Ford, Pennsylvania, established a tea room on French Street in Wilmington, Delaware, where she sold cakes, fruit, and desserts to wealthy people for their parties. Her son, Jeremiah Shadd, was a butcher, well-known for his ability to cure meat. His wife, known as Aunt Sallie Shadd, achieved legendary status among Wilmington's free black population as the inventor of ice cream. The story was that the butcher Jeremiah purchased Sallie's freedom. Like other members of her family, she went into the catering business and created a new dessert sensation made from frozen cream, sugar, and fruit. Dolly Madison, the wife of President James Madison, heard about the new dessert, came to Wilmington to try it, and afterward made ice cream a feature of dinners at the White House."

"About 1926 the first commercially-successful continuous process freezer was perfected. The continuous freezer, developed by Clarence Vogt, and later ones produced by other manufacturers, has allowed the ice cream industry to become a mass producer of its product."

The first Canadian to start selling ice cream was Thomas Webb of Toronto, a confectioner, around 1850. William Neilson produced his first commercial batch of ice cream on Gladstone Ave. in Toronto in 1893, and his company produced ice cream at that location for close to 100 years.

After writing this page, I received the following email message:

Date: Thu, 06 Jun 1996
From: Anne Funderburg 

For a documented history of ice cream in the United States, read the just published "Chocolate, Strawberry, and Vanilla: A History of American Ice Cream" by Anne Funderburg. This book sheds new light on errors created by previous historians. For example, Nancy Johnson lived in Philadelphia and she did have a patent! To order, call Bowling Green State University Popular Press at (419) 372-7865 or fax (419) 372-8095.
The Funderburg book is solely concerned with ice cream history in the United States, and does not discuss any of these earlier myths, although it does give an excellent history of ice cream development in the United States.

Another excellent source of reading on the history and folklore of ice cream is by Paul Dickson, The Great American Ice Cream Book.

Here are links to web pages devoted to the history of the ice cream cone:

Ice Cream Cone

ThoughtCo. - History of Ice Cream

Further on the ice cream cone:

From: RobinWeir1@aol.com 
Date: August 30, 2004 
Subject: THE ICE CREAM CONE

Dear Professor Goff,

At the Ice Screamers convention (Note: as association that celebrates ice cream parlour and soda fountain memorabilia, the leading organization of ice cream collectibles - DG) in July I gave a paper on the ice cream cone and the fact that it was in use in Paris in 1807. Yes 1807. We are planning the celebration of the bicentenary of the cone in 2007. I am happy to send you all details, prints of engravings and references if you would like.

Kindest regards
Robin Weir.

Subject: Award from "Surfing the Net with Kids" 
From: Barbara J. Feldman, feldman@surfnetkids.com 
To: dgoff@uoguelph.ca 

Congratulations! Your site (Ice Cream History and Folklore) has been rated "Great!" and awarded 3 stars in my syndicated newspaper column "Surfing the Net with Kids". My column appears in many papers nationally including San Diego Union-Tribune, Atlanta Journal-Constitution, Indianapolis Star News, Contra Costa Times and Winston Salem Journal. 

Sincerely,
Barbara J. Feldman
"Surfing the Net with Kids"
 

Ice Cream Production and Consumption Data

The World Scene

World production and consumption data that is easily comparable is difficult to find, due to wide variations in methods of reporting (volume, weight) and in categories of products included or excluded from the data. The table below shows annual ice cream consumption data (per capita, in litres) from selected countries.

Source: Goff and Hartel, 2013. 

Consumption of Ice Cream (2010) {Note: both dairy- and non-dairy-fat based products are included}

Country Litres per capita
Australia 17.9
New Zealand 15.8
United States 14.2
Finland 12.5
Canada 10.5
Italy 10.0
Norway 9.8
United Kingdom 8.6
Denmark 8.4
Chile 8.0
World 2.4
China 2.1

The Canadian Scene

Some statistical data is presented below, which is now updated regularly and available at Agriculture and Agri-Food Canada, Canadian Dairy Information Centre

Canadian Ice Cream Mix Production, kL 

1988    166,252                 
1989    161,073         
1990    162,905         
1991    161,394         
1992    149,203
1993    164,210
1994    175,579
1995    172,678
1996    166,296
1997    154,974
1998    154,803
1999    152,542
2000    137,869
2001    147,450
2002    158,470
2003    150,696
2004    154,778
2005    172,699
2006    171,271
2007    146,789
2008    129,151
2009    109,399
2010    111,953
2011    106,849
2012    102,782
2013    90,459

 

Note: this is milkfat-based ice cream only. Since 2006, Frozen Dessert products have been on the market that are vegetable fat-based, rather than milkfat-based, and these are not captured in the statistics above. Frozen desserts due contain milk solids-not-fat, however. The dramatic effect these have had on ice cream production per se is illustrated by the numbers in the table below.

Provincial Ice Cream Mix Production, 2006 vs. 2012  

Ontario      108,698 vs. 57,680
Others(1)     62,573 vs. 52,343
(1) Not disclosed to protect individual company data.

Per capita consumption - hard and soft ice cream  

1980   12.72            
1985   12.02            
1990   11.50            
1995   11.39    
1996   10.88
1997   10.35
1998   10.19
1999    10.03
2000    8.63
2001    9.23
2002    9.49
2003    9.26
2004    9.15
2005    9.85
2006    9.23
2007    8.03
2008    6.90
2009    5.54
2010    5.51
2011    5.49
2012    5.56
2013    5.12

Note: again, this is milkfat-based ice cream only and does not include consumption of Frozen Dessert products,  which are vegetable fat-based, rather than milkfat-based.

Source: Agriculture and Agri-Food Canada, Canadian Dairy Information Centre

The Scene from the United States

US Production of Ice Cream, Hard and Soft; Regular, Lowfat and Nonfat, Million Gallons 

1990 1175.9
1991 1204.4
1992 1194.3
1993 1191.5
1994 1234.7
1995 1262.9
1996 1286.2
1997 1340.1
1998 1384.6
1999 1393.3
2000 1383.7
2001 1372.7
2002 1364.6
2003 1411.5
2004 1329.7
2005 1340.9
2006 1352.9
2010 1318.4

US Per Capita consumption of Ice Cream - Hard and Soft; Regular, Lowfat and Nonfat, litres (excluding imports and exports) 

1990 17.9
1995 17.9
2000 18.6
2001 18.2
2002 18.0
2003 18.4
2004 17.0
2005 16.9
2006 17.2
2010 16.2

Source: United States Dept. of Agriculture Economic Research Service.

US hard and Soft Ice Cream, Million Gallons, by State, 2006 

California 160
Texas 97
Indiana 87
Pennsylvania 54
Massachusetts 54
Minnesota 53


- The Top 5 States produced about 33% of the United States production.          
Source: International Dairy Foods Association, Dairy Facts 2007.

Ice Cream Formulations

Ice Cream Mix General Composition

 (See details under mix ingredients.)

  • Milkfat: >10% - 16%
  • Milk solids-not-fat (snf): 9% - 12%
  • Sucrose: 10% - 14%
  • Corn syrup solids: 4% - 5%
  • Stabilizers: 0% - 0.4%
  • Emulsifiers: 0% - 0.25%
  • Water: 55% - 64%

The snf contains, on average, dry wt. basis, 38% protein, 54% lactose, and 8% ash (including 1.38% Ca, 1.07% P, 1.22% K, 0.7% Na).

Formulation Considerations

First of all, regulatory issues. What are the product definitions for your legal jurisdiction? These, of course, have to be met.

Next, desired Fat and Total solids (%): - Quality considerations, what kind of product are you trying to make?

Fat: MSNF Ratio's usually determined next based on fat content.

Sugar: Glucose solids Ratio's determined based on fat and total solids requirements, sweetness, freezing point depression, body and shelf life desired, and cost considerations.

Stabilizer/Emulsifier considerations come last, based on the ice cream formulation, and processing and distribution factors involved in each application.

With these considerations in mind, it is also useful to look at ranges of components for the categories of products in the ice cream category that are available in the market. These are industry-used terms, not legally defined.

Economy Brands

  • Fat content, usually legal minimum, e.g., 10%
  • Total solids, usually legal minimum, e.g., 36%
  • Overrun, usually legal maximum, ~120%
  • Cost, low

Standard Brands

  • Fat content, 10-12%
  • Total solids, 36-38%
  • Overrun, 100-120%
  • Cost, average

Premium Brands

  • Fat content, 12-15%
  • Total solids, 38-40%
  • Overrun, 60-90%
  • Cost, higher than average

Super-premium Brands

  • Fat content, 15-18%
  • Total solids, >40%
  • Overrun, 25-50%
  • Cost, high

Suggested Mixes

Below are composition tables, based on mix components. To convert these to recipes based on ingredients to be used, please see the section on mix calculations.

If you are looking for recipes, please see the section on homemade ice cream

A standard base recipe could consist of 30% heavy cream (35% fat), 50% whole milk (3.25% fat), 4% skim milk powder, 15% sugar and 1% egg yolk.

Suggested mixes for hard-frozen ice cream products.

Percent (%)
Milk Fat 10.0 11.0 12.0 13.0 14.0 15.0 16.0
Milk Solids-not-fat 11.0 11.0 10.5 10.5 10.0 10.0 9.5
Sucrose 10.0 10.0 12.0 14.0 14.0 15.0 15.0
Corn Syrup Solids 5.0 5.0 4.0 3.0 3.0 - -
Stabilizer* 0.35 0.35 0.30 0.30 0.25 0.20 0.15
Emulsifier* 0.15 0.15 0.15 0.14 0.13 0.12 0.10
Total Solids 36.5 37.5 38.95 40.94 41.38 40.32 40.75

*Highly variable depending on type; manufacturers recommendations are usually followed.

  • Usually an inverse relationship between fat and total solids compared to snf
  • Generally an inverse relationship between glucose solids (corn sweetener) levels and total solids
  • As total solids increases, there is less requirement for stabilizer
  • As fat levels in a mix increase, there is generally less need for emulsifier

Suggested mixes for low-fat (3-5% fat) and light (6-8% fat) ice cream products.

Percent (%)
Milk Fat 3.0 4.0 5.0 6.0 8.0
Milk Solids-not-fat 13.0 12.5 12.5 12.0 11.5
Sucrose 11.0 11.0 11.0 13.0 12.0
Corn Syrup Solids 6.0 5.5 5.5 4.0 4.0
Stabilizer 0.35 0.35 0.35 0.35 0.35
Emulsifier 0.10 0.10 0.10 0.15 0.15
Total Solids 33.65 33.45 34.45 35.5 36.0

Ice milk was the traditional lower fat ice cream product for many years, but this category has been re-classified by many regulatory jurisdictions to include three reduced fat categories: light ice cream, lowfat ice cream (the traditional ice milk), and non-fat ice cream. It has generally been possible to produce fat contents as low as 4% with traditional products, but further fat reductions have generally involved fat-replacers.

Suggested mixes for soft-frozen ice cream products.

Percent (%)
Milk Fat 10.0 10.0
Milk Solids-not-fat 12.5 12.0
Sucrose 13.0 10.0
Corn Syrup Solids --- 4.0
Stabilizer* 0.35 0.15
Emulsifier* 0.15 0.15
Total Solids 36.0 36.3

 *Highly variable depending on type; manufacturers recommendations are usually followed.

Generally, while the fat content is kept lower, the snf content is generally higher than for hard-frozen products.

  • Glucose solids are often used, but can lead to an enhanced sensation of guminess.
  • Stabilizers are also generally used for viscosity enhancement and mouthfeel, but their function in ice recrystallization is no longer needed.
  • Dryness, however, is a big concern in soft-serve products, hence the emulsifier content is generally kept high.

Sherbet and Sorbet

Percent (%)
Milk Fat 0.5 1.5
Milk Solids-not-fat 2.0 3.5
Sucrose 24.0 24.0
Corn Syrup Solids 9.0 6.0
Stabilizer/emulsifier* 0.3 0.3
Citric acid (50% sol.)** 0.7 0.7
Water 63.5 64.0
Total 100.0 100.0
  • * Or as advised from the supplier.
  • ** Acid is added just before freezing, after aging of the mix.
  • Sorbet: delete the mix and skim powder
  • Fruit: at about 25% to the mix. 

Frozen Yogurt

Percent (%)
Fat 2.0
MSNF 14.0
Sugar 15.0
Stabilizer 0.35
Water 68.65
Total 100.0
  • Example Processing Instructions: 20% of this mix, consisting of skimmilk and skimmilk powder blended to give 12.5% solids, is to be incubated as the yogurt portion.
  • To make the "incubated" portion, combine the appropriate amount of skimmilk and skimmilk powder, pasteurize at a high temperature, cool to 104 to 110F, and inoculate with a yogurt culture (typical of yogurt processing). When the fermentation is complete (to the desired acidity), cool the "yogurt".
  • To make the "sweet" mix, combine the cream, sugar and stabilizer, and the balance of the skimmilk powder and skimmilk, pasteurize, homogenize, cool (typical for ice cream processing), and blend with the "yogurt".
  • The completed frozen yogurt mix is then aged and prepared for flavouring and freezing.

Frozen yogurt in many legal jurisdictions is an unstandardized product, so there are no legally-defined characteristics. However, in keeping with the connotation of a real "yogurt", which we have come to accept as a fermented dairy product, two characteristics that should be met for a frozen yogurt include:

  • The presence of live culture;
  • Developed (from fermentation) acidity.

Ice Cream Mix Ingredients

Ice cream has the following composition:

  • greater than 10% milkfat by legal definition, and usually between 10% and as high as 16% fat in some premium ice creams
  • 9 to 12% milk solids-not-fat (MSNF): this component, also known as the serum solids, contains the proteins (caseins and whey proteins) and carbohydrates (lactose) found in milk
  • 12 to 16% sweeteners: usually a combination of sucrose and glucose-based corn syrup sweeteners
  • 0.2 to 0.5% stabilizers and emulsifiers
  • 55% to 64% water which comes from the milk or other ingredients

These percentages are by weight, either in the mix or in the frozen ice cream. Please remember, however, that when frozen, about one half of the volume of ice cream is air (overrun, for definition, see ice cream processing, for calculation, see overrun), so by volume in ice cream, these numbers can be reduced by approximately one-half, depending on the actual air content. However, since air does not contribute weight, we usually talk about the composition of ice cream on a weight basis, bearing in mind this important distinction. All ice cream flavours, with the possible exception of chocolate, are made from a basic white mix.

Formulations can be derived from a number of different starting points. Details and suggested formulas are detailed on the formulations page, but turning the formulation into a recipe depends on the ingredients used to supply the components, and it is then necessary to do a mix calculation to determine the required ingredients based on the formula. Ice milk and light ice creams are very similar to the composition of ice cream but in the case of ice milk in Canada, for example, it must contain between 3% and 5% milkfat by legal definition.

The ingredients to supply the desired components are chosen on the basis of availability, cost, and desired quality. These ingredients will now be examined in more detail.

Milkfat (or "Butterfat") / Fat

Milkfat, or fat in general, including that from non0dairy sources, is important to ice cream for the following reasons:

  • increases the richness of flavour in ice cream (milkfat more so than non-dairy fats)
  • produces a characteristic smooth texture by lubricating the palate
  • helps to give body to the ice cream, due to its role in fat destabilization
  • aids in good melting properties, also due to its role in fat destabilization
  • aids in lubricating the freezer barrel during manufacturing (Non-fat mixes are extremely hard on the freezing equipment)

The limitations of excessive use of butterfat in a mix include:

  • cost
  • hindered whipping ability
  • decreased consumption due to excessive richness
  • high caloric value

The best source of butterfat in ice cream for high quality flavour and convenience is fresh sweet cream from fresh sweet milk. Other sources include butter or anhydrous milkfat.

During freezing of ice cream, the fat emulsion which exists in the mix will partially destabilize or churn as a result of the air incorporation, ice crystallization and high shear forces of the blades. This partial churning is necessary to set up the structure and texture in ice cream, which is very similar to the structure in whipped cream. Emulsifiers help to promote this destabilization process, which will be discussed below.

The triglycerides in milkfat have a wide melting range, +40° C to -40° C, and thus there is always a combination of liquid and crystalline fat. Alteration of this solid: liquid ratio can affect the amount of fat destabilization that occurs. Duplicating this structure with other sources of fat is difficult.

Vegetable (non-dairy) fats are used extensively as fat sources in ice cream in the United Kingdom, parts of Europe, the Far East, and Latin America but only to a very limited extent in North America. Five factors of great interest in selection of fat source are the crystal structure of the fat, the rate at which the fat crystallizes during dynamic temperature conditions, the temperature-dependent melting profile of the fat, especially at chilled and freezer temperatures, the content of high melting triglycerides (which can produce a waxy, greasy mouthfeel) and the flavor and purity of the oil. It is important that the fat droplet contain an intermediate ratio of liquid:solid fat at the time of freezing. It is difficult to quantify this ratio as it is dependent on a number of composition and manufacturing factors, however, 1/2 to 2/3 crystalline fat at 4-5oC is a good, working rule. Crystallization of fat occurs in three steps: undercooling to induce nucleation, heterogeneous or homogeneous nucleation (or both), and crystal propagation. In bulk fat, nucleation is predominantly heterogeneous, with crystals themselves acting as nucleating agents for further crystallization, and undercooling is usually minimal. However, in an emulsion, each droplet must crystallize independently of the next. For heterogeneous nucleation to predominate, there must be a nucleating agent available in every droplet, which is often not the case. Thus in emulsions, homogeneous nucleation and extensive undercooling may be common. Blends of oils are often used in ice cream manufacture, selected to take into account physical characteristics, flavor, availability, stability during storage and cost.

We have recently completed a study on the use of non-dairy fats in frozen desserts. A blend of 75% of either fractionated palm kernel oil or coconut oil and 25% of an unsaturated oil, like high oleic sunflower oil, was shown to produce optimal levels of fat destabilization, meltdown and flavour, although coconut oil may take longer to crystallize during aging. Blends of 50% milkfat, 37.5% fractionated palm kernel or coconut oil, and 12.5% high oleic sunflower oil were also shown to be very acceptable.

Milk Solids-not-fat

The serum solids or milk solids-not-fat (MSNF) contain the lactosecaseins, whey proteins, and minerals (ash content) of the product from which they were derived. They are an important ingredient for the following beneficial reasons:

  • improve the texture of ice cream, due to the protein functionality
  • help to give body and chew resistance to the finished product
  • are capable of allowing a higher overrun without the characteristic snowy or flaky textures associated with high overrun, due also to the protein functionality
  • may be a cheap source of total solids, especially whey powder

The limitations on their use include off flavours which may arise from some of the products, and an excess of lactose which can lead to the defect of sandiness prevalent when the lactose crystallizes out of solution. Excessive concentrations of lactose in the serum phase may also lower the freezing point of the finished product to an unacceptable level.

The best sources of serum solids for high quality products are:

  • concentrated skimmed milk
  • spray process low heat skim milk powder

Other sources of serum solids include: sweetened condensed whole or skimmed milk, frozen condensed skimmed milk, buttermilk powder or condensed buttermilk, condensed whole milk, or dried or condensed whey. Superheated condensed skimmed milk, in which high viscosity is promoted, is sometimes used as a stabilizing agent but does, then, also contribute to serum solids.

It has recently become common practice to replace the use of skim milk powder or condensed skim with a variety of milk powder replacers, which are blends of whey protein concentrates, caseinates, and whey powders. These are formulated with less protein than skim powder, usually 20-25% protein, and thus less cost, but are blended with an appropriate balance of whey proteins and caseins to do an adequate job. Caution must be exercised in excessive use of these powders, experimentation with your own mix is the best answer.

See the section on Concentrated and Dried Dairy Products for a description of the manufacture of all of the above ingredients.

The proteins, which make up approximately 4% of the mix, contribute much to the development of structure in ice cream including:

  • emulsification properties in the mix
  • whipping properties in the ice cream
  • water holding capacity leading to enhanced viscosity and reduced iciness

Lactose Crystallization

  1. A decrease in temperature favours rapid crystallization insofar as it increases the supersaturation.
  2. A decrease in temperature favours slow crystallization insofar as it increases the viscosity, reduces the kinetic energy of the particles, and decreases the rate of transformation from beta to alpha lactose.

Supersaturated state can exist, however, due to extreme viscosity, and it is likely that much of the lactose in ice cream is non-crystalline. Stabilizers help to hold lactose in supersaturated state due to viscosity enhancement. Fruits, nuts, candy - add crystal centers and may enhance lactose crystallization. Nuts pull out moisture from ice cream immediately surrounding the nut thus concentrating the mix.

Citrate and phosphate ions decrease tendency for fat coalescence (Sodium citrate, Disodium Phosphate). They prevent churning in soft ice cream for example, producing a wetter product. These salts decrease the degree of protein aggregation. Calcium and magnesium ions have the opposite effect, promote partial coalescence. Calcium sulfate, for example, results in a drier ice cream. Calcium and Magnesium increase the degree of protein aggregation.
Salts may also influence electrostatic interactions. Fat globules carry a small net negative charge, these ions could increase or decrease that charge as they were attracted to or repelled from surface.

Sweeteners

 A sweet ice cream is usually desired by the consumer. As a result, sweetening agents are added to ice cream mix at a rate of usually 12 - 16% by weight. Sweeteners improve the texture and palatability of the ice cream, enhance flavors, and are usually the cheapest source of total solids.

In addition, the sugars, including the lactose from the milk components, contribute to a depressed freezing point so that the ice cream has some unfrozen water associated with it at very low temperatures typical of their serving temperatures, -15° to -18° C. Without this unfrozen water, the ice cream would be too hard to scoop. See also the discussion of freeze concentration in the ice cream structure section. The effect of sweeteners on freezing characteristics of ice cream mixes is demonstrated by the plot shown on the ice cream freezing curve.

Sucrose is the main sweetener used because it imparts excellent flavour. Sucrose is a disaccharide made up of glucose (dextrose, cerelose), and fructose (levulose). Sucrose is dextrorotatory - meaning it rotates a plane of polarized light to the right, + 66.5° . With hydrolyzed sucrose the plane of polarization is to the left, "inverted" -20° . An acid, plus water, plus heat treatment, at concentrations above 10%, yields invert sugar and increases the sweetness.

It has become common in the industry to substitute all or a portion of the sucrose content with sweeteners derived from corn syrup. This sweetener is reported to contribute a firmer and more chewy body to the ice cream, is an economical source of solids, and improves the shelf life of the finished product. Corn syrup in either its liquid or dry form is available in varying dextrose equivalents (DE). The DE is a measure of the reducing sugar content of the syrup calculated as dextrose and expressed as a percentage of the total dry weight. As the DE is increased by hydrolysis of the corn starch, the sweetness of the solids is increased and the average molecular weight is decreased. This results in an increase in the freezing point depression, in such foods as ice cream, by the sweetener. The lower DE corn syrup contains more dextrins which tie up more water in the mix thus supplying greater stabilizing effect against coarse texture.

Diagram illustrating the effect of DE and maltose or fructose conversion on the properties of corn starch hydrolysates as used in ice creamAn enzymatic hydrolysis and isomerization procedure can convert glucose to fructose, a sweeter carbohydrate, in corn syrups thus producing a blend (high fructose corn syrup, HFCS) which can be used to a much greater extent in sucrose replacement. However, these HFCS blends further reduce the freezing point producing a very soft ice cream at usual conditions of storage and dipping in the home.

On the right is a diagram illustrating the effect of DE and maltose or fructose conversion on the properties of corn starch hydrolysates as used in ice cream.

A balance is involved between sweetness, total solids, and freezing point.

Stabilizers

The stabilizers are a group of compounds, usually polysaccharide food gums, that are responsible for adding viscosity to the mix and the unfrozen phase of the ice cream. This results in many functional benefits, listed below, and also extends the shelf life by limiting ice recrystallization during storage. Without the stabilizers, the ice cream would become coarse and icy very quickly due to the migration of free water and the growth of existing ice crystals. 

Graph showing the effects of stabilizers on size of ice crystals in ice cream

The smaller the ice crystals in the ice cream, the less detectable they are to the tongue. Especially in the distribution channels of today's marketplace, the supermarkets, the trunks of cars, and so on, ice cream has many opportunities to warm up, partially melt some of the ice, and then refreeze as the temperature is once again lowered (see also the discussion on the fundamental aspects of freezing and ice cream shelf life for a more in-depth look at this process, and some discussion regarding the role of stabilizers in inhibiting it). This process is known as heat shock and every time it happens, the ice cream becomes more icy tasting. Stabilizers help to prevent this.

The functions of stabilizers in ice cream are:

  • In the mix: To stabilize the emulsion to prevent creaming of fat and, in the case of carrageenan, to prevent serum separation due to incompatibility of the other polysaccharides with milk proteins, also to aid in suspension of liquid flavours
  • In the ice cream at draw from the scraped surface freezer: To stabilize the air bubbles and to hold the flavourings, e.g., ripple sauces, in dispersion
  • In the ice cream during storage: To prevent lactose crystal growth and retard or reduce ice crystal growth during storage (see also the discussion on ice cream shelf life, which discusses the mode of action of stabilizers in affecting ice recrystallization), also to prevent shrinkage from collapse of the air bubbles and to prevent moisture migration into the package (in the case of paperboard) and sublimation from the surface
  • In the ice cream at the time of consumption: To provide some body and mouthfeel without being gummy, and to promote good flavour release
  • (Note: all of the above, except perhaps for their role in retarding ice crystallization, can be attributable to the viscosity increase in the unfrozen phase of the ice cream)

Limitations on their use include:

  • production of undesirable melting characteristics, due to too high viscosity
  • excessive mix viscosity prior to freezing
  • contribution to a heavy or chewy body

The stabilizers in use today include:

Locust Bean Gum:

soluble fibre of plant material derived from the endosperm of beans of exotic trees grown mostly in Africa (Note: locust bean gum is a synonym for carob bean gum, the beans of which were used centuries ago for weighing precious metals, a system still in use today, the word carob and Karat having similar derivation)

Guar Gum:

from the endosperm of the bean of the guar bush, a member of the legume family grown in India for centuries and now grown to a limited extent in Texas

Carboxymethyl cellulose (CMC):

derived from the bulky components, or pulp cellulose, of plant material, and chemically derivatized to make it water soluble

Xanthan gum:

produced in culture broth media by the microorganism Xanthaomonas campestris as an exopolysaccharide, used to a lesser extent

Sodium alginate:

an extract of seaweed, brown kelp, also used to a lesser extent

Carrageenan:

an extract of Irish Moss or other red algae, originally harvested from the coast of Ireland, near the village of Carragheen but now most frequently obtained from Chile and the Phillipines

Each of the stabilizers has its own characteristics and often, two or more of these stabilizers are used in combination to lend synergistic properties to each other and improve their overall effectiveness. Guar, for example, is more soluble than locust bean gum at cold temperatures, thus it finds more application in HTST pasteurization systems. Carrageenan is not used by itself but rather is used as a secondary colloid to prevent the wheying off of mix which is usually promoted by one of the other stabilizers.

Gelatin, a protein of animal origin, was used almost exclusively in the ice cream industry as a stabilizer but has gradually been replaced with polysaccharides of plant origin due to their increased effectiveness and reduced cost.

Emulsifiers

Diagram showing a desorption of protein from the fat droplet surfaceThe emulsifiers are a group of compounds in ice cream that aid in developing the appropriate fat structure and air distribution necessary for the smooth eating and good meltdown characteristics desired in ice cream. Since each molecule of an emulsifier contains a hydrophilic portion and a hydrophobic portion, they reside at the interface between fat and water. As a result they act to reduce the interfacial tension or the force which exists between the two phases of the emulsion. This causes a desorption of protein from the fat droplet surface, which promotes a destabilization of the fat emulsion (due to a weaker membrane) leading to a smooth, dry product with good meltdown properties (see diagram on the right). Their action will be more fully explained in the structure of ice cream section.

The original ice cream emulsifier was egg yolk, which was used in most of the original recipes. Today, two emulsifiers predominate most ice cream formulations:

mono- and di-glycerides:

derived from the partial hydrolysis of fats or oils of animal or vegetable origin

polysorbate 80:

a sorbitan ester consisting of a glucose alcohol (sorbitol) molecule bound to a fatty acid, oleic acid, with oxyethylene groups added for further water solubility

Other possible sources of emulsifiers include buttermilk, and glycerol esters. All of these compounds are either fats or carbohydrates, important components in most of the foods we eat and need. Together, the stabilizers and emulsifiers make up less than one half percent by weight of our ice cream. They are all compounds which have been exhaustively tested for safety and have received the "generally recognized as safe" or GRAS status.

Mix Calculations for Ice Cream and Frozen Dairy Desserts

The general objective in calculating ice cream mixes is to turn your formula into a recipe based on the ingredients you intend to use and the amount of mix you desire. The formula is given as percentages of fat, milk solids-not-fat, sugar, corn syrup solids (glucose solids), stabilizers and emulsifiers. The ingredients to supply these components are chosen on the basis of availability, quality and cost. The following table illustrates the relationship between the major components, the main ingredients that supply the major components, and the minor components that are supplied with the major ones for each ingredient.

Component and Ingredients to supply that component (but note that each of these ingredients also supplies the following other components):

Milkfat, supplied by Cream (which also supplies SNF and water) or Butter (which also supplies SNF, water);

Milk solids-not-fat (SNF, or sometimes also called serum solids, S.S.), supplied by any of the following:

  • Skim powder (which also supplies water, about 3%)
  • Condensed skim (which also supplies water)
  • Condensed milk (which also supplies water and fat)
  • Sweetened condensed (which also supplies water and sugar)
  • Whey powder (which also supplies water)

Water, supplied by Skim milk (which also supplies msnf), or milk (which also supplies fat and msnf), or pure water.

Sweetener, supplied by dry or liquid (which also then supplies water) sucrose or corn syrup solids.

The first step in a mix calculation is to identify for each ingredient we intend to use its components. If there is only one source of the component we need for the formula, for example the stabilizer or the sugar, we determine it directly by multiplying the percentage we need by the amount we need, e.g., 100 kg of mix @ 10% sugar would require 10 kg sugar. If there are two or more sources, for example we need 10 % fat and it is coming from both cream and milk, then we need to utilize an algebraic method.

Computer programs developed for mix calculations generally solve a simultaneous equation based on mass and component balances. To solve simultaneous equations, you need as many independent equations as you have unknowns. For an example of a free on-line mix calculator, see http://www.dairyscience.info/newcalculators/calculator/index.php.

For manual calculations, a method known as the "Serum Point" method has been derived. This method has solved the simultaneous equations in a general way so that only the equations need to be known and not resolved each time.

In standardizing mixes, the composition of the various ingredients used must be known. In some cases the percentage of solids contained in a product is taken as constant, while in others the composition must be obtained by analysis. Information on the various ingredients is given below:

(a) Skim milk - can be determined by analysis or assumed at 9 percent serum solids. Fat (0.01% - 0.10%) should be taken into account if significant.

(b) Dried products, e.g. skim milk powder, whey powder, WPC, milk powder blends, usually taken to be 97 percent solids as they retain some moisture.

(c) Cream - Percent fat usually measured by an acceptable method.

Percent MSNF found by formula as follows: (100 - percent fat) x .09 = % snf (assuming that the "skim milk" contains 9% total solids). Example: In cream testing 30% fat, the percent snf would be (100 - 30) x .09 = 6.3% snf

(d) Milk - Percent fat measured by an acceptable method.

Percent snf may be found same as for cream or by making a total solids test and deducting the percent fat.

(e) Condensed Milk Products - Composition of these products should be obtained by the supplier.

(f) Sweeteners - Sucrose - Dry 100% solids
Sucrose - Liquid 66% solids
Dextrose - Dry 100% solids
Corn Syrup Solids 100% solids
Corn Syrup Liquid 80% solids
Glucose 80% solids
Honey 80% solids

(g) Stabilizers and Emulsifiers (if solid) - Because of the small percentage used may be figured as 100 percent solids.

(h) Egg Products - Fresh whole eggs: 10% fat, 25% solids
Fresh egg yolk: 33% fat, 50% solids
Frozen egg yolk: 33% fat, 50% solids
Dried egg yolk: 60% fat, 100% solids

Problems

Below are some example problems to look at, if you are interested in the mathematics of mix calculations. 

  • Example 1. Basic mix using butter, skim powder, and water (only one source of each component). (Algebraic Method)
  • Example 2. Mix using cream, skim, and skim powder (three sources of milk SNF, three sources of water). (Algebraic and Serum Point Methods)
  • Example 3. Mix using cream, milk, and skim powder (three sources of milk SNF, three sources of water, and two source of fat). (Algebraic and Serum Point Methods)
  • Example 4. Mix using cream, milk, and sweetened, condensed skim (three sources of milk SNF, three sources of water, two sources of fat, and two sources of sugar). (Serum Point Method)
  • Example 5. Mix using cream, milk, and sweetened, condensed milk (three sources of milk SNF, three sources of water, three sources of fat, and two sources of sugar). (Serum Point Method)
  • Example 6. Mix using a given amount of cream and skim, with the balance coming from butter, milk, and skim powder. (Serum Point Method)
  • Example 7. Mix using cream, milk, condensed skim, and liquid sweeteners (water needs to be accounted for). (Serum Point Method)

After completing a problem, you should do a proof of your calculation, by ensuring that the mass sums to the desired value, and that the mass fraction of all components also sum to the desired value - see all the examples below. There is only one unique solution, so you know by calculation if you have it right or not!

Note: these are all solved on the basis of 100 kg. If you are making more or less than that, you can still solve on the basis of 100 kg and then scale up or down your answer accordingly (by dividing your answers per 100 kg by 100 and multipying by the actual wt., e.g. 45 kg cream/100 kg mix, if you are making 4000 kg, it would be 45/100*4000=180 kg cream) , or you can use the desired weight directly in the calculations, but be careful with the serum point method equations - see Example 3 below. If you have scaled up or down from 100 kg, you should do the proof total on the desired weight, and ensure it meets the desired percentage - see Example 3 or 6.

I am sometimes asked how to incorporate whole milk powder into mix calculations. This is common in some parts of the world. I will attach a pdf file below that shows such a calculation.

Problem 1

Desired: 100 kg mix testing 14% fat, 10% MSNF, 15% sucrose, 0.4% stabilizer/ emulsifier.

Ingredients on hand: Butter 80% fat, skim milk powder 97% solids, water sucrose, stabilizer/emulsifier.

Solution:

1. Find the amount of butter required to supply 14 kg of fat/ 100 kg mix,

14 kg fat x 100 kg butter/80 kg fat = 17.5 kg butter

2. Find the amount of skim milk powder needed to supply a total of 10 kg of snf/ 100 kg mix.

The butter contributes 17.5 kg butter x 1.8 kg s.s / 100 kg butter = 0.315 kg s.s.

Powder must contribute 10 kg snf - 0.315 kg = 9.685 kg s.s.

9.685 kg snf x 100 kg powder/97 kg snf = 9.98 kg powder

3. Sucrose required will be 15.0 kg/ 100 kg mix.

4. Stabilizer/ emulsifier required will be 0.4 kg/ 100 kg mix.

5. The amount of water required will be equal to 100 minus the sum of the weights of the other ingredients, thus,

100 - (17.5 + 9.98 + 15 + 0.4) = 57.12 kg water

Note: In Problem 1, the serum solids content of the butter was calculated as follows: butter at 80% fat, remaining 20% skim milk at 9% milk solids-not-fat, therefore msnf in butter = 20% x 9% = 1.8%.

In the manufacture of butter, fat is churned from cream (which can be thought of as a mixture of fat and skim milk). If no washing of the butter is performed after churning, the above assumption of 1.8% msnf in 80% fat butter is correct. However, the 20% skim milk could be substituted wholly or in part with wash water, which would reduce the msnf level to anywhere between 1.8% and 0%. Each butter sample either needs to be analyzed for solids or an assumption of no msnf should be made to assure that at least the required msnf is supplied from other ingredients.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Total Solids (kg)
Butter 17.50 14.00 0.32 14.32
Skim powder 9.98 -- 9.68 9.68
Sucrose 15.00 -- -- 15.00
Stabilizer 0.40 -- -- 0.40
Water 57.12 -- -- --
Totals 100.00 14.00 10.00 39.40

Note: 14% fat + 10% msnf + 15% sucrose + 0.4% stab. = 39.4% TS

Problem 2

Desired : 100 kg mix @ 13% fat, 11% MSNF, 15% sucrose, 0.5% stabilizer, 0.15% emulsifier

On hand: Cream @ 40% fat, 5.4% msnf; skimmilk @ 9% msnf; skimmilk powder @ 97% msnf; sugar; stabilizer; emulsifier.

Solution: (Note: only one source of fat, sugar, stabilizer, and emulsifier, but two sources of serum solids)

Cream:
100 kg mix x 13 kg fat/100 kg mix x 100 kg cream/40 kg fat = 32.5 kg cream

Sucrose:
100 kg mix x 15 kg sucrose/100 kg mix = 15 kg sucrose

Stabilizer:
100 kg mix x 0.5 kg stabilizer/100 kg mix = 0.5 kg stabilizer

Emulsifier:
100 kg mix x 0.15 kg emulsifier/100 kg mix = 0.15 kg emulsifier

Algebraic method:

Skim milk and Skim powder, Note: two sources of the MSNF

Now, let x = skim powder, y = skim milk

MASS BALANCE (All the components add up to 100 kg)

x + y = 100 - (32.5 + 15 + 0.5 + 0.15) (1)

MSNF BALANCE (Equal to 11% of the mix and coming from the skim milk, the skim powder, and the cream)

0.97 x + 0.09 y = .11(100) - (.054 x 32.5) (2)
x + y = 51.85 so y = 51.85 - x from (1)
.97 x + .09 y = 9.245 from (2)
.97 x + .09 (51.85 - x) = 9.245 substituting 
.97 x - .09 x + 4.67 = 9.245
.88 x = 4.58

x = 5.20 kg skim powder

y = 46.65 kg skim milk

The above shows the solution of a 2-unknown simultaneous equation. Likewise, if there were 3 unknowns, e.g., fat, msnf, and the total weight, then three equations could be written, one for each of fat, msnf, and weight. However, the above problem could also be solved with the Serum Point method, and the example and that solution along with the derivation of the equations follows. The Serum Point calculation assumes 9% msnf in skimmilk and the skim portion of all dairy ingredients. It then solves the calculation beginning with the most concentrated source of serum solids first.

Solution via the serum point method:

1. Amount of powdered skim milk needed is found by the following formula:

(SNF needed - (serum of mix X .09))/(% SNF in powder - 9) X 100 = kg skim powder

This is a generalized equation solved from a mas balance, that works in all situations where milk powder is the most concentrated source of serum solids, and all of the serum products are milk products (i.e., there is no water used in the recipe). An assumption is that the serum fraction of all dairy ingredients contains 9% solids-not-fat, e.g., 40% cream contains 60% skim (100-40), which contains 9% snf, so the snf content of the cream is .60 x .09 = 5.4%

The serum of the mix is found by adding the desired percentages of fat, sucrose, stabilizer and emulsifier together and subtracting from 100. In the present problem then,

100 - (13 + 15 + 0.5 + 0.15) = 71.35 kg serum.

Substituting in the formula we have:

(11 - (71.35 x .09))/(97 - 9) x 100 = 4.58/88 x 100 = 5.20 kg skim powder

2. The weight of cream will be 13 kg x 100 kg cream/40 kg fat = 32.5 kg cream

3. The sucrose will be 15 kg/ 100 kg mix.

4. The stabilizer will be 0.5 kg/ 100 kg mix.

5. The emulsifier will be 0.15 kg/ 100 kg mix.

6. The weight of mix supplied so far is,

Cream 32.50 kg
Skim powder 5.20 kg
Sucrose 15.00 kg
Stabilizer .50 kg
Emulsifier .15 kg
Total 53.35 kg

The skim milk needed therefore is 100 - 53.35 = 46.65 kg.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Total Solids (kg)
Cream 32.50 13.00 1.75 14.75
Skim milk 46.65 -- 4.20 4.20
Skim milk powder 5.20 -- 5.04 5.04
Sucrose 15.00 -- -- 15.00
Stabilizer 0.50 -- -- 0.50
Emulsifier 0.15 -- -- 0.15
Totals 100.00 13.00 11.00 39.64

Note: 13% fat + 11% snf + 15% sucrose + 0.50% stab. + 0.15% emul. = 39.65% TS

DERIVATION OF THE SERUM POINT EQUATIONS: Let's resolve problem 2 again using simultaneous equations in a general way to show where the serum point equations come from.

On hand: cream @ 40% fat
(supplies fat, water, and serum solids, therefore can be thought of as a mixture of fat and skim milk)
skim milk @ 9% solids not fat
(supplies water and serum solids) 
skim milk powder @ 97% solids not fat
(supplies water and serum solids) 
sucrose
stabilizer
emulsifier

Solution

- Only one source of fat, sucrose, stabilizer, and emulsifier

kg fat = 100 kg mix x 13 kg fat/100 kg mix = 13 kg fat (The explanation for this assumption becomes clearer in a moment!)

kg sucrose = 100 kg mix x 15 kg sucrose/100 kg mix = 15 kg sucrose

kg stabilizer = 100 kg mix x 0.5 kg stab./100 kg mix = 0.5 kg stabilizer

kg emulsifier = 100 kg mix x 0.15 kg emul./100 kg mix = 0.15 kg emulsifier

- Two sources of serum solids

Let X = skim powder (kg)
Let Y = skim milk (kg) + skim milk in cream (kg)

MASS BALANCE X + Y = Total mix - components already added
X + Y = 100 - (13 + 15 + 0.5 + 0.15), (the "Serum of the Mix")
X + Y = 71.35
(so Y = 71.35 - X)

 

MSNF BALANCE 0.97X + 0.09Y = (0.11 x 100)
"Serum "Serum "Serum fraction
fraction fraction in mix"
in powder" in skim"

0.97 X + 0.09 (71.35 - X) = 11
0.97 X + (0.09 x 71.35) - 0.09 X = 11
0.97 X - 0.09 X = 11 - (0.09 x 71.35)
X = 11 - (.09 x 71.35)/ 0.97 - 0.09

Which is equal to:

 

kg skim powder = S.S. needed - (0.09 x serum of mix) x 100 % S.S. in powder - 9

X = 4.58/0.88 = 5.20 kg powder

kg cream = 13 kg fat x 100 kg cream/40 kg fat = 32.5 kg cream

kg skim = 100 - 32.5 - 15 - 0.5 - 0.15 - 5.2 = 46.65 kg

Problem 3

Desired: 100 kg mix containing 18% fat, 9.5% SNF, 15% sucrose, 0.4% stabilizer, 1% frozen egg yolk.

On hand: Cream 30% fat, milk 3.5% fat, skim milk powder 97% solids, sucrose, stabilizer, and egg yolk.

The solution to this problem will be shown by simultaneous equations, since there are three sources of milk SNF, three sources of water, and two source of fat, which require three equations, and by the serum point method. Both produce the same results. Follow whichever method you prefer. Computer programs exist that solve simultaneous equations.

Solution via the algebraic method:

Sucrose: 100 kg mix x 15 kg sucrose/100 kg mix = 15 kg sucrose

Stabilizer: 100 kg mix x 0.4 kg stabilizer/100 kg mix = 0.4 kg stabilizer

Egg yolk: 100 kg mix x 1 kg egg yolk/100 kg mix = 1 kg egg yolk

Now, let x = skim powder, y = milk, z = cream.

MASS BALANCE All the components add up to 100 kg

x + y + z = 100 - (15 + 0.4 + 1) (1)

MSNF BALANCE Equal to 9.5% of the mix and coming from the milk, the skim powder, and the cream; assume 9% in the skim portion of the milk and cream so that the msnf of the milk = .09 x (100 - 3.5) and of the cream = .09 x (100-30)

0.97 x + 0.08685 y + 0.063 z = .095 (100) (2)

FAT BALANCE Equal to 18% of the mix and coming from the milk and cream

.035 y + .3 z = .18 (100) (3)

Solution via the serum point method:

1. Find the amount of skim milk powder required by the following formula:

(SNF needed - (serum of mix x .09))/(% SNF in powder - 9) x 100 = skim powder

Substituting we have,

(9.5 - ( 65.6 x .09 ))/(97-9) x 100 = 3.596/88 x 100 = 4.08 kg powder

2. Amount of sucrose required is 15.0 kg.

3. Amount of stabilizer required is .4 kg.

4. Amount of egg required is 1.0 kg.

5. Find weight of milk and cream needed.

Materials supplied so far are 4.08 kg powder, 15 kg sucrose, 0.4 kg stabilizer, and 1 kg egg yolk, a total of 20.48 kg. 100 - 20.48 = 79.52 kg milk and cream needed.

6. Find the amount of cream by following formula:

((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100

substituting we have,

(18 - ( 79.52 x 3.5/100 ))/(30-3.5) x 100 = 15.217/26.5 x 100 = 57.42 kg cream.

7. Amount of milk needed = 79.52 - 57.42 = 22.10 kg of milk.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Total Solids (kg)
Cream 57.42 17.23 3.62 20.85
Milk 22.10 0.77 1.92 2.69
Skim milk powder 4.08 -- 3.96 3.96
Sucrose 15.00 -- -- 15.00
Stabilizer 0.40 -- -- 0.40
Egg Yolk 1.00 -- -- 0.50
Totals 100.00 18.00 9.50 43.40

Note: 18% fat + 9.5% snf + 15% sucrose + 0.40% stab. + 0.50% egg yolk solids (half the egg yolk) = 43.4% TS

If you wanted to make 3000 kg (for example) instead of 100 kg, you could multiply all of the numbers above by 30, or you could set up the equation to solve directly for 3000 kg, as shown below.

Solution via the serum point method for 3000 kg:

1. Find the amount of skim milk powder required by the following formula:

(MSNF needed - (serum of mix x .09))/(% snf in powder - 9) x 100 = skim powder

MSNF needed = 3000 x 9.5% = 285 kg; Serum of the mix = 3000 - 540 (fat) - 450 (sugar) - 12 (stab.) - 30 (egg yolk) = 1968 kg. Substituting we have,

(285 - ( 1968 x .09 ))/(97-9) x 100 = 107.88/88 x 100 = 122.59 kg powder

2. Amount of sucrose required is 3000 x 15% = 450.0 kg.

3. Amount of stabilizer required is 3000 x.4% = 12.0 kg.

4. Amount of egg required is 3000 x 1.0% = 30 kg.

5. Find weight of milk and cream needed.

Materials supplied so far are 122.59 kg powder, 450.0 kg sucrose, 12.0 kg stabilizer, and 30.0 kg egg yolk, a total of 614.59 kg. 3000 - 614.59 = 2385.41 kg milk and cream needed.

6. Find the amount of cream by following formula:

((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100

substituting we have,

(540 - ( 2385.41 x 3.5/100 ))/(30-3.5) x 100 = 456.51/26.5 x 100 = 1722.68 kg cream.

7. Amount of milk needed = 2385.41 - 1722.68 = 662.73 kg of milk.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Total Solids (kg)
Cream 1722.68 516.8 108.53 625.33
Milk 662.73 23.2 57.56 80.76
Skim milk powder 122.59 -- 118.91 118.91
Sucrose 450.00 -- -- 450.00
Stabilizer 12.0 -- -- 12.0
Egg Yolk 30.0 -- -- 15.0
Totals 3000.0 540.0 285.0 1302.0

Note: 540/3000 = 18% fat; 285/3000 = 9.5% SNF; 1302/3000 = 43.4% Total solids

Problem 4

Desired: 100 kgs. mix testing 14% fat, 10% MSNF, 15% sucrose, 0.5% stabilizer/emulsifier.

On hand: Cream 32% fat, milk 3.5% fat, sweetened condensed skim milk 28% serum solids and 40% sugar, sucrose and stabilizer.

Solution via the Serum Point Method :

1. Find amount of condensed skim milk required by the following formula:

(SNF needed - (serum of mix x .09))/( % SNF in cond. - (serum of cond. x .09)) x 100 = sweet cond. skim milk

Note: Serum of condensed is calculated the same as serum of mix, i.e., 100 - (Fat + Sugar + Stab.)

Substituting we have:

(10 - ( 70.5 x .09 ))/(28 - ( 60 x .09 )) x 100 = 16.17 kg cond. skim milk

2. Find amount of sucrose needed:

16.17 x .40 = 6.47 kg of sucrose in the condensed milk.
15 - 6.47 = 8.53 kg of sucrose still needed.

Note: If you added too much sugar by using sweetened condensed skim to supply the desired serum solids, then scale back the sweetened condensed skim to supply all the sugar you need and make up the deficiency in serum solids with skim powder.

3. Amount of stabilizer required is 0.5 kg.

4. Find weight of milk and cream needed.

Material so far supplied is, 16.17 kg condensed milk, 8.53 kg sugar and .5 kg stabilizer, a total of 25.2 kg.
100 - 25.2 = 74.8 kg milk and cream required.

5. Find amount of cream by the following formula:

((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100

Substituting we have:
(14 - ( 74.8 x .035 ))/(32 - 3.5) x 100 = 39.93

6. Find milk required:

74.8 - 39.93 = 34.87 kgs. milk.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Sugar (kg) Wt. of Total Solids (kg)
Cream 39.93 12.78 2.44 -- 15.22
Milk 34.87 1.22 3.03 -- 4.25
Swt. Cond. Milk 16.17 -- 4.53 6.47 11.00
Sucrose 8.53 -- -- 8.53 8.53
Stabilizer 0.50 -- -- -- 0.50
Totals 100.00 14.00 10.00 15.00 39.50

Note: 14% fat + 10% snf + 15% sucrose + 0.5% stab = 39.5% TS

Problem 5

Desired: 100 kg mix testing 14% fat, 10% MSNF, 15% sucrose, 0.5% stabilizer/ emulsifier.

On hand: Cream 30% fat; milk 4% fat; sweetened condensed whole milk 8% fat, 20% snf, 42% sugar; stabilizer/ emulsifier; and sucrose.

Solution via the Serum Point Method:

1. Find the amount of sweetened condensed milk by formula:

(SNF needed - (serum of mix X .09))/(% SNF in cond. - (% serum in cond. X .09)) X 100 = kg cond. milk

Substituting we have:

(10 - (70.5 X .09))/(20 - (50 X .09)) X 100 = 23.58 kg sweetened cond. milk

2. Stabilizer/ emulsifier required will be 0.5 kg.

3. Find amount of sucrose needed.

23.58 X .42 = 9.90 kg sucrose in cond. milk.
15 - 9.90 = 5.1 kg sucrose still required.

Note: If you added too much sugar by using sweetened condensed skim to supply the desired serum solids, then scale back the sweetened condensed skim to supply all the sugar you need and make up the deficiency in serum solids with skim powder.

4. Find amount of milk and cream needed.

100 - 29.18 (cond. milk, sugar, and stabilizer) = 70.82 kg.

5. Find amount of cream required.

23.58 X .08 = 1.89 kg fat in the condensed milk.
14 - 1.89 = 12.11 kg fat still needed.

Use formula:

((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100

Substituting we have:

(12.11 - (70.82 X .04)) / (30 - 4) X 100 = 35.69 kg cream

6. Find amount of milk required:

70.82 - 35.69 = 35.13 kg milk.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Sugar (kg) Wt. of Total Solids (kg)
Cream 35.69 10.71 2.25 -- 12.96
Milk 35.13 1.40 3.03 -- 4.43
Swt. Cond. Milk 23.58 1.89 4.72 9.90 16.51
Sucrose 5.10 -- -- 5.10 5.10
Stabilizer 0.50 -- -- -- 0.50
Totals 100.00 14.00 10.00 15.00 39.50

Note: Note: 14% fat + 10% snf + 15% sucrose + 0.5% stab = 39.5% TS

Problem 6

Desired: Make 2000 kg of mix testing 15% fat, 10.5% MSNF, 15% sucrose, 0.5% stabilizer, 1% egg yolk

From the following: 450 kgs. 30% cream; 300 kgs. skim milk; Get balance from butter @ 84% fat, milk @ 4% fat, skim milk powder, sucrose, stabilizer, and egg yolk.

Solution via the Serum Point Method:

1. Find skim milk powder needed.

Use formula:

(SNF needed - (serum of mix X .09)) / (% snf in powder - 9 ) X 100

Substituting we have:

(210 - (1370 X .09)) / (97 - 9) X 100 = 98.5 kg powder

2. Find sugar, stabilizer, and egg needed.

2000 X .15 = 300 kg sucrose
2000 X .005 = 10 kg stabilizer
2000 X .01 = 20 kg egg yolk

3. List the materials supplied so far:

Cream               450.00 kg
Skim Milk          300.00 kg
Skim Powder       98.50 kg
Sucrose             300.00 kg
Stabilizer           10.00 kg
Egg Yolk           20.00 kg

Total                1,178.50 kg

4. Find amount of butter and milk needed.

2000 - 1178.5 = 821.5 kg butter and milk required.

5. Find amount of fat that still has to be made up:

300 - 135 (Fat in 450 kg 30% cream) = 165 kg

6. Find amount of butter needed by following formula:

((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100

Substituting we have:

(165 - (821.5 X .04)) / (84 - 4 ) X 100 = 165.17 kg butter

7. Find amount of milk needed.

821.5 - 165.17 = 656.33 kg milk

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Total Solids (kg)
Cream 450.00 135.00 28.35 163.35
Milk 656.33 26.25 56.71 82.96
Butter 165.17 138.74 2.37 140.39
Skim Milk 300.00 -- 27.00 27.00
Skim milk powder 98.50 -- 95.55 95.55
Sucrose 300.00 -- -- 300.00
Stabilizer 10.00 -- -- 10.00
Egg Yolk 20.00 -- -- 10.00
Totals 2000.00 300.00 210.00 829.25

Note: 300/2000 = 15% fat; 210/2000 = 10.5% SNF; 829.25/2000 = 41.46% Total solids (= 15% fat + 10.5% snf + 15% sucrose + 0.5% stab + 0.5% egg yolk solids (half of the egg yolk))

Problem 7 (Using Liquid Sweeteners)

Desired: 100 kgs. of mix testing 12% fat, 11% MSNF, 14% sucrose, 3% corn syrup solids, 0.35% stabilizer, 0.15% emulsifier.

On hand: Cream 40% fat; milk 3.5% fat; condensed skim milk 35% solids; liquid sucrose 66% solids; regular conversion corn syrup 80% solids; stabilizer; emulsifier.

Solution via the Serum Point Method:

1. Calculate the pounds of condensed skim first, but determine serum of the mix as follows:

(a) Find the amount of liquid sucrose that must be added to provide 14 kg of sucrose solids:

14 kg sucrose x 100 kg liq. sucrose/66 kg sucrose = 21.21 kg.

(b) Find the amount of corn syrup that must be added to provide 3 kgs. of corn syrup solids:

3 kg solids x 100 kg liq. css/80 kg solids = 3.75 kg.

Serum of the mix is found by adding together the percentage of fat, liquid sucrose, liquid corn syrup, stabilizer and emulsifier and subtracting from 100:

  • 12.00 kg fat
  • 21.21 kg liquid sucrose
  • 3.75 kg corn syrup
  • 0.35 kg stabilizer
  • 0.15 kg emulsifier

Total 37.46 kg

100 - 37.46 = 62.54, the serum of the mix

Use formula:

(SNF needed - ( serum of mix x .09 )) / (% SNF in Cond. skim - 9) x 100

Substituting we have:

(11 - ( 62.54 x .09 )) / (35 - 9) x 100 = 20.65 kg of condensed skimmilk

2. Liquid sucrose required = 21.21 kg.

3. Liquid corn syrup required = 3.75 kg.

4. Stabilizer required = 0.35 kg.

5. Emulsifier required = 0.15 kg.

6. Find the amount of milk and cream needed:

100 - (20.65 + 21.21 + 3.75 + 0.35 + 0.15) = 53.89 kg.

7. Find the amount of cream needed by formula:

((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100

Substituting we have:

(12 - ( 53.89 x 3.5/100 ))/(40 - 3.5) x 100 = 27.69 kg of cream.

8. Find the amount of milk required:

53.89 - 27.69 = 26.20 kgs. of milk.

PROOF:

Ingredient Total wt. (kg) Wt. of Fat (kg) Wt. of SNF (kg) Wt. of Sugar (kg) Wt. of Total Solids (kg)
Cream 27.69 11.08 1.50 -- 12.58
Milk 26.20 0.92 2.27 -- 3.19
Cond. Skim 20.65 -- 7.23 -- 7.23
Sucrose 21.21 -- -- 14.00 14.00
Corn syrup solids 3.75 -- -- 3.00 3.00
Stabilizer 0.35 -- -- -- 0.35
Emulsifier 0.15 -- -- -- 0.15
Totals 100.00 12.00 11.00 17.00 40.50

Note: 12% fat + 11% snf + 14% sucrose + 3.0% css + 0.35% stab + 0.15% emul. = 40.5% TS

Ice Cream Manufacture

The basic steps in the manufacturing of ice cream are generally as follows:

  • blending of the mix ingredients
  • pasteurization
  • homogenization
  • aging the mix
  • freezing
  • packaging
  • hardening

Process flow diagram for ice cream manufacture

Process flow diagram for ice cream manufacture: the red section represents the operations involving raw, unpasteurized mix, the pale blue section represents the operations involving pasteurized mix, and the dark blue section represents the operations involving frozen ice cream.

Blending

First the ingredients are selected based on the desired formulation and the calculation of the recipe from the formulation and the ingredients chosen, then the ingredients are weighed and blended together to produce what is known as the "ice cream mix". Blending requires rapid agitation to incorporate powders, and often high speed blenders are used.

diagram of a a simple hopper device for incorporating dry ingredients into recirculating liquids

Diagram of a high shear blender for incorporating dry ingredients into recirculating liquids

Pasteurization of Mix

The mix is then pasteurized. Pasteurization is the biological control point in the system, designed for the destruction of pathogenic bacteria. In addition to this very important function, pasteurization also reduces the number of spoilage organisms such as psychrotrophs, and helps to hydrate some of the components (proteins, stabilizers). 

Pasteurization (Ontario regulations): 69° C/30 min. 80° C/25s 

Both batch pasteurizers and continuous (HTST) methods are used.

Batch pasteurizers lead to more whey protein denaturation, which some people feel gives a better body to the ice cream. In a batch pasteurization system, blending of the proper ingredient amounts is done in large jacketed vats equipped with some means of heating, usually steam or hot water. The product is then heated in the vat to at least 69 C (155 F) and held for 30 Diagram of an HTST continuous plate pasteurizerminutes to satisfy legal requirements for pasteurization, necessary for the destruction of pathogenic bacteria. Various time temperature combinations can be used. The heat treatment must be severe enough to ensure destruction of pathogens and to reduce the bacterial count to a maximum of 100,000 per gram. Following pasteurization, the mix is homogenized by means of high pressures and then is passed across some type of heat exchanger (plate or double or triple tube) for the purpose of cooling the mix to refrigerated temperatures (4 C). Batch tanks are usually operated in tandem so that one is holding while the other is being prepared. Automatic timers and valves ensure the proper holding time has been met.

Continuous pasteurization (see schematic diagram for mix to the right) is usually performed in a high temperature short time (HTST) heat exchanger following blending of ingredients in a large, insulated feed tank. Some preheating, to 30 to 40 C, is necessary for solubilization of the components. The HTST system is equipped with a heating section, a cooling section, and a regeneration section. Cooling sections of ice cream mix HTST presses are usually larger than milk HTST presses. Due to the preheating of the mix, regeneration is lost and mix entering the cooling section is still quite warm.

Homogenization of Mix

The mix is also homogenized, which forms the fat emulsion by breaking down or reducing the size of the fat globules found in milk or cream to less than 1 µ m. Two stage homogenization is usually preferred for ice cream mix. Clumping or clustering of the fat is reduced thereby producing a thinner, more rapidly whipped mix. Melt-down is also improved. Homogenization provides the following functions in ice cream manufacture:

  • Reduces size of fat globules
  • Increases surface area
  • Forms membrane
  • makes possible the use of butter, frozen cream, etc.

By helping to form the fat structure, it also has the following indirect effects:

  • makes a smoother ice cream
  • gives a greater apparent richness and palatability
  • better air stability
  • increases resistance to melting

Homogenization of the mix should take place at the pasteurizing temperature. The high temperature produces more efficient breaking up of the fat globules at any given pressure and also reduces fat clumping and the tendency to thick, heavy bodied mixes. No one pressure can be recommended that will give satisfactory results under all conditions. The higher the fat and total solids in the mix, the lower the pressure should be. If a two stage homogenizer is used, a pressure of 2000 - 2500 psi on the first stage and 500 - 1000 psi on the second stage should be satisfactory under most conditions. Two stage homogenization is usually preferred for ice cream mix. Clumping or clustering of the fat is reduced thereby producing a thinner, more rapidly whipped mix. Melt-down is also improved.

Ageing of Mix

The mix is then aged for at least four hours and usually overnight. This allows time for the fat to cool down and crystallize, and for the proteins and polysaccharides to fully hydrate. Aging provides the following functions:

  • Improves whipping qualities of mix and body and texture of ice cream

It does so by:

  • providing time for fat crystallization, so the fat can partially coalesce;
  • allowing time for full protein and stabilizer hydration and a resulting slight viscosity increase;
  • allowing time for membrane rearrangement and protein/emulsifier interaction, as emulsifiers displace proteins from the fat globule surface, which allows for a reduction in stabilization of the fat globules and enhanced partial coalescence.

Aging is performed in insulated or refrigerated storage tanks, silos, etc. Mix temperature should be maintained as low as possible without freezing, at or below 5 C. An aging time of overnight is likely to give best results under average plant conditions. A "green" or unaged mix is usually quickly detected at the freezer.

Freezing/Whipping of Ice Cream

Following mix processing, the mix is drawn into a flavour tank where any liquid flavours, fruit purees, or colours are added. The mix then enters the dynamic freezing process which both freezes a portion of the water and whips air into the frozen mix. The "barrel" freezer is a scraped-surface, tubular heat exchanger, which is jacketed with a boiling refrigerant such as ammonia or freon. Mix is pumped through this freezer and is drawn off the other end in a matter of 30 seconds, (or 10 to 15 minutes in the case of batch freezers) with about 50% of its water frozen. There are rotating blades inside the barrel that keep the ice scraped off the surface of the freezer and also dashers inside the machine which help to whip the mix and incorporate air.

Diagram of a continuous ice cream (barrel) freezer

Ice cream contains a considerable quantity of air, up to half of its volume. This gives the product its characteristic lightness. Without air, ice cream would be similar to a frozen ice cube. The air content is termed its overrun, which can be calculated mathematically.

As the ice cream is drawn with about half of its water frozen, particulate matter such as fruits, nuts, candy, cookies, or whatever you like, is added to the semi-frozen slurry which has a consistency similar to soft-serve ice cream. In fact, almost the only thing which differentiates hard frozen ice cream from soft-serve, is the fact that soft serve is drawn into cones at this point in the process rather than into packages for subsequent hardening.

Hardening

 After the particulates have been added, the ice cream is packaged and is placed into a blast freezer at -30° to -40° C where most of the remainder of the water is frozen. Below about -25° C, ice cream is stable for indefinite periods without danger of ice crystal growth; however, above this temperature, ice crystal growth is possible and the rate of crystal growth is dependant upon the temperature of storage. This limits the shelf life of ice cream.

A primer on the theoretical aspects of freezing will help you to fully understand the freezing and recrystallization process.

Hardening invloves static (still, quiescent) freezing of the packaged products in blast freezers. Freezing rate must still be rapid, so freezing techniques involve low temperature (-40oC) with either enhanced convection (freezing tunnels with forced air fans) or enhanced conduction (plate freezers).

Spiral wind tunnel freezer diagram

The rate of heat transfer in a freezing process is affected by the temperature difference, the surface area exposed and the heat transfer coefficient (Q=U A dT). Thus, the factors affecting hardening are those affecting this rate of heat transfer:

  • Temperature of blast freezer - the colder the temperature, the faster the hardening, the smoother the product.
  • Rapid circulation of air - increases convective heat transfer.
  • Temperature of ice cream when placed in the hardening freezer - the colder the ice cream at draw, the faster the hardening; - must get through packaging operations fast.
  • Size of container - exposure of maximum surface area to cold air, especially important to consider shrink wrapped bundles - they become a much larger mass to freeze. Bundling should be done after hardening.
  • Composition of ice cream - related to freezing point depression and the temperature required to ensure a significantly high ice phase volume.
  • Method of stacking containers or bundles to allow air circulation. Circulation should not be impeded - there should be no 'dead air' spaces (e.g., round vs. square packages).
  • Care of evaporator - freedom from frost - acts as insulator.
  • Package type, should not impede heat transfer - e.g., styrofoam liner or corrugated cardboard may protect against heat shock after hardening, but reduces heat transfer during freezing so not feasible.

Ice cream from the dynamic freezing process (continuous freezer) can also be transformed into an array of novely/impulse products through a variety of filling and forming machines, which have ben identified on a separate page.

Ice Cream Novelty/Impulse Products

Molded Novelties

Ice cream novelties are typically single-serving items bought from vendors for immediate consumption. They come in a variety of shapes, sizes, colours, flavours, etc., and manufacturers are constantly developing new items to compete for market share. hence, this category is variably known as either impulse products or novelty products. These products can be manufactured by a number of processes.

Products such as popsicles or ice cream with flat sides on sticks are manufactured by filling a mold with water ice or soft ice cream from a barrel freezer, immersion freezing that mold in a cold bath of calcim chloride solution, inserting the stick when partially hardened, and then after hardening is complete, removal of the ice cream from the mold by the stick.

Point 1 = filling;
Point 2 = partial freezing as the molds progress in the calcium chloride bath - you can have an optional "suck-out" of unfrozen material and refillng of something else at this stage;
point 3 = stick insertion - the product is now frozen sufficiently to hold the stick in place;
point 4 = furthr freezing as the molds progress in the calcium chloride bath - you can insert ribbon sauces anywhere along this stage, until the product gets too hard;
point 5 = withdrawal of the mold from the calcium chloride bath, a quick defrost to free the bar from the mold wall, and extraction of the product from the mold by grabbing the stick - after which the product can be coated with nuts, enrobed with chocolate, then packaged, and on to storage.

The molds continue underneath the machinewhere they are washed, rinsed, and sanitized, ready for the next filling.

Vitaline Frozen Novelty Production diagram

I am indebted to Mr. Malcolm Storey for drawing this illustration for me. Thanks!

Extruded Novelties

Products with no sticks, like bars with fancy shapes, or with sticks but irregular sides, such that they could not be pulled out of a mold, are frozen by extrusion. In such a process, the shape is formed and sliced, either vertically or horizontally as below, that slice is further hardenend by passing it through a cold tunnel, and then nuts or syrup can be coated on it, it can be enrobed with chocolate sauce, or whatever is desired to give the final product. Horizontal extrusion is used to make the "chocolate bar analogue" type of products, while vertical extrusion is used to make everythng from chocolate-enrobed ice cream slices to fancy-shaped novelties on a stick.

Diagram of a horizontal extrusion and a vertical extrusion

Overrun calculations

In looking at calculating overrun in ice cream, it is important to remember the definition of overrun; that is, it is the % increase in volume of ice cream greater than the amount of mix used to produce that ice cream. In other words, if you start off with 1 litre of mix and you make 1.5 litres of ice cream from that, you have increased the volume by 50% (i.e., the overrun is 50%). Equations are as follows:

Figuring plant overrun by volume, no particulates

% Overrun = (Vol. of ice cream - Vol. of mix used)/Vol. of mix used x 100%

Example : 500 L mix gives 980 L ice cream,
(980 - 500)/500 x 100% = 96% Overrun

80 L mix plus 10 L chocolate syrup gives 170 L chocolate ice cream,

(Note : any flavours added such as this chocolate syrup which become homogeneous with the mix can incorporate air and are thus accounted for in this way : )

(170 - (80 + 10))/(80 + 10) x 100% = 88.8% Overrun

Figuring plant overrun by volume, with particulates

Example : 40 L mix plus 28 L pecans gives 110 L butter pecan ice cream,

110 - 28 = 82 L actual ice cream.

% Overrun = (Vol. of ice cream - Vol. of mix used)/Vol. of mix used 
= (82 - 40)/40 x 100% = 105% 

(Note : The pecans do not incorporate air.)

Figuring package overrun by weight, no particulates

 % Overrun = (Wt. of mix - Wt. of same vol. of ice cream )/Wt. of same vol. of ice cream x 100%

Must know density of mix (wt. of 1 L), usually 1.09 - 1.1 kg. /L.

(see example below)

Example : If 1 L of ice cream weighs 560 g,
% Overrun = (1090 - 560)/560 x 100% = 94.6% Overrun

(Note : Figuring package overrun by weight if the ice cream has particulates in it gives very little information because both the ratio of ice cream to particulates and the air content of the ice cream affect the final weight.)

Figuring mix density

The density of mix can be calculated as follows: 

1 / ((% fat/100 x 1.075) + ((% T.S./100 - % Fat/100) x 0.63) + (% Water/100)) = Wt. (kg)/ litre mix

Example - Calculate the weight per litre of mix containing 12% fat, 11% serum solids, 10% sugar, 5% corn syrup solids, 0.30% stabilizer, and 38.3% T.S.

1.0  / ((0.12 x 1.075) + ((0.383 - 0.12) x 0.63) + 0.617) = 1.096 kg/L of mix

Figuring target package weights, no particulates

Weight of given vol. of ice cream = Wt. of same vol. of mix / (Desired overrun / 100 + 1)

Example : Desired 90% Overrun, mix density 1.09 kg/L
net wt. of 1 L = 1.09 kg / ( 90/100 + 1) = 573.7 g

Also, density of ice cream = density of mix / (Overrun/100 + 1)

Example: Density of mix 1100 g/L,

@100% Overrun, density of ice cream = 1100 g/L / (100/100 + 1) = 550 g/L

Figuring target package weights, with particulates

Example : Butter brickle ice cream; density of mix 1.1 kg/L; overrun in ice cream 100%; density of candy 0.748 kg/L; candy added at 9% by weight, (i.e. 9 kg to 100 kg final product)

In 100 kg final product, we have:

9 kg of candy (or 9 kg / 0.748 kg/L = 12.0 L)

91 kg of ice cream (or 91 kg / (1.1 kg/L / (100/100 + 1)) = 165.4 L)

So, 100 kg gives a yield of 12 + 165.4 = 177.4 L

1 L weighs 100 kg / 177.4 L = 564 grams 

(Note : In many cases, ice cream of different flavours is frozen to the same weight. As a result, overrun of actual ice cream in product varies.)

Developing an Overrun Table for Use When Manufacturing Ice Cream

To develop an overrun table to determine overrun quickly by weight when making ice cream, all you need is a cup with a fixed volume that is convenient for filling ice cream into (like a steel measuring cup, for example, with a flat top that would be easy to scrape level) and an ordinary gram balance. Then, using the equation from above, you can calculate what the weight of the cup would be for a series of different overruns, and then make up a table. Then when you are running ice cream, just keep weighing the cup and checking against the table for the overrun in the cup.

% Overrun = (Wt. of mix - Wt. of same vol. of ice cream )/Wt. of same vol. of ice cream x 100%

So, lets say your cup holds 100 mL. Fill the cup with mix and weigh it. Let's say the net weight (minus the weight of the empty cup) is 110 g. Lets say the empty cup weighs 30 g.

The net weight of the cup at 5% overrun would be:
.05 = (110 - x)/x, solve for x and you get 104.8, so the gross weight would be 134.8 g.

{In case your algebra is rusty, to solve for x, follow this example:
.05 = (110-x)/x
x = (110-x)/.05
x = 110/.05 - x/.05
x = 2200 - 20x
x + 20x = 2200
21x = 2200
x = 2200/21 = 104.76}

Likewise for 10%, 0.1 = (110 - x)/x, solve for x and you get 100, so the gross weight would be 130 g.

Keep going up to 150% or so, then make a table:

Overrun%           Weight of cup + ice cream (grams)

0                              140
5                              134.8
10                            130
.
.
.
150                            74

Ice Cream Structure

Ice cream structure is both fascinating and confusing. The way we perceive the texture of ice cream when we consume it (smooth, coarse, etc.) is based on its structure, and thus structure is probably one of its most important attributes.

Colloidal aspects of ice cream structure

Please look at

Digram of fat structure in ice cream

Diagram of replacing proteins on the fat surfacewhen reading the following description, and try to put the two together in your mind. Also, please look at the last paragraph of this page for links to electron micrographic images of the structure of ice cream.

Ice cream is both an emulsion and a foam. The milkfat exists in tiny globules that have been formed by the homogenizer. There are many proteins that act as emulsifiers and give the fat emulsion its needed stability. The emulsifiers are added to ice cream to actually reduce the stability of this fat emulsion by replacing proteins on the fat surface (shown on the right), leading to a thinner membrane more prone to coalescence during whipping. When the mix is subjected to the whipping action of the barrel freezer, the fat emulsion begins to partially break down and the fat globules begin to flocculate or destabilize. The air bubbles which are being beaten into the mix are stabilized by this partially coalesced fat. If emulsifiers were not added, the fat globules would have so much ability to resist this coalescing, due to the proteins being adsorbed to the fat globule, that the air bubbles would not be properly stabilized and the ice cream would not have the same smooth texture (due to this fat structure) that it has.

Graph of effect of emulsifier on fat destabilization in ice cream

This fat structure which exists in ice cream is the same type of structure which exists in whipped cream. When you whip a bowl of heavy cream, it soon starts to become stiff and dry appearing and takes on a smooth texture. This results from the formation of this partially coalesced fat structure stabilizing the air bubbles. If it is whipped too far, the fat will begin to churn and butter particles will form. The same thing will happen in ice cream which has been whipped too much.

Ice Cream Meltdown

One of the important manifestations of ice cream structure is its melt-down. When you put ice cream in an ambient environment to melt (as in a scoop on a plate), two events occur; the melting of the ice and the collapse of the fat-stabilized foam structure. The melting of the ice is controlled by the outside temperature (fast on a hot day) and the rate of heat transfer (faster on a hot, windy day). However, even after the ice crystals melt, the ice cream does not "melt" (collapse) until the fat-stabilized foam structure collapses, and that is a function of the extent of fat destabilization/partial coalescence, which is controlled mostly by the emulsifier concentration, for reasons we have just described above.

This is shown in the diagram below, which shows ice cream sitting on a mesh screen at ambient temperature:

diagram showing ice cream sitting on a mesh screen at ambient temperature

You can see above the increased amount of shape retention and slowness of melt that comes from the added emulsifiers, particularly polysorbate 80.

Structure from the Ice crystals

Also adding structure to the ice cream is the formation of the ice crystals. Water freezes out of a solution in its pure form as ice. In a sugar solution such as ice cream, the initial freezing point of the solution is lower than 0° C due to these dissolved sugars (freezing point depression), which is mostly a function of the sugar content of the mix. As ice crystallization begins and water freezes out in its pure form, the concentration of the remaining solution of sugar is increased due to water removal and hence the freezing point is further lowered. This process is shown here, schematically.

The process of the formation of ice crystalsThis process of freeze concentration continues to very low temperatures. Even at the typical ice cream serving temperature of -16° C, only about 72% of the water is frozen. The rest remains as a very concentrated sugar solution. Thus when temperature is plotted against % water frozen, you get the phase diagram shown below. This helps to give ice cream its ability to be scooped and chewed at freezer temperatures. The air content also contributes to this ability, as mentioned in discussing overrun.

 

 

 

 

 

 

 

Graph showing the effects of sweeteners on freezing characteristics of ice cream mixesThe effect of sweeteners on freezing characteristics of ice cream mixes is demonstrated by the plot shown on the ice cream freezing curve.

Also critical to ice cream structure is ice crystal size, and the effect of recrystallization (heat shock, temperature fluctuations) on ice crystal size and texture. A primer on the theoretical aspects of freezing will help you to fully understand the freezing process. Please see the discussion and diagram on ice crystallization rate, as shown on that page, to fully understand this process. Recrystallization (growth) of ice is discussed elsewhere in the context of shelf life.

Thus the structure of ice cream can be described as a partly frozen foam with ice crystals and air bubbles occupying a majority of the space. The tiny fat globules, some of them flocculated and surrounding the air bubbles also form a dispersed phase. Proteins and emulsifiers are in turn surrounding the fat globules. The continuous phase consists of a very concentrated, unfrozen solution of sugars. One gram of ice cream of typical composition contains 1.5 x 1012 fat globules of average diameter 1µ m that have a surface area of greater than 1 square meter (in a gram!), 8 x 106 air bubbles of average diameter 70 µ m with a surface area of 0.1 sq. m., and 8 x 106 ice crystals of average diameter 50 µ m with a surface area of another 0.1 sq. m. The importance of surface chemistry becomes obvious!

Microscopy

Before we leave ice cream structure, I want to draw your attention to the following address: "Foods Under the Microscope". This is a link to an absolutely marvelous website developed by my good friend Dr. Milos Kalab, with many high-quality images of the structure of milk and dairy products obtained during Dr. Kalab's long and outstanding career as a food microscopist with Agriculture and Agri-Food Canada in Ottawa. Dr. Kalab asked me to contribute microscopic images of ice cream structure as a guest microscopist. You can find my (Doug Goff) first contribution under "Guest microscopists", and I have also copied it here. Subsequent to that submission, I have prepared another one for D. Kalab that focuses on the use of cryo-fixation and TEM for visualization of fat and air structures in ice cream. One of my graduate students, Alejandra Regand, also made a contribution, based on her M.Sc. thesis work, focusing on the structure of polysaccharides in frozen solutions.

Ice cream structure is an active area of our research here at the University of Guelph. Please see my publications for more details of our research.

Theoretical Aspects of the Freezing Process

The Process of Crystallization

This section will briefly review the physico-chemical processes that occur during a freezing process. The figure below shows the time-temperature relationship for freezing of pure water (ABCDE) and aqueous solutions (AB'C'D'). The first thermal event that can be seen from such a diagram is undercooling below the freezing point before the induction of crystallization, from A to B or B' . This is a non-equilibrium, metastable state which is analogous to an activation energy necessary for the nucleation process. Pure water can be undercooled by several degrees before the nucleation phenomenon begins.

Graph of temperature and time for the process of crystallization

Once the critical mass of nuclei is reached, the system nucleates at point B or B' in the figure and releases its latent heat faster than heat is being removed from the system. In aqueous solutions, however, B' is not as low as B, since the added solute will promote heterogeneous nucleation, thereby accelerating the nucleation process. The temperature increases instantly to the initial freezing temperatureof the solution at Point C (0oC) or C' (Tf). The presence of solutes results in depression of the freezing point based on Raoult's Law, which relates vapor pressure of the solution to that of pure solvent based on solute concentration. Note that C' is not as high as C, because the initial freezing point is depressed as a result of the solute. Hence, the solute has greatly decreased the amount of undercooling for two reasons: faster nucleation and lowered freezing point. In very concentrated solutions, it is sometimes even difficult to induce undercooling.

In pure water, the time line from C to D in the figure reflects the time during which crystal growth is occurring at 0oC. Fast freezing rates promote the formation of many small ice crystals during this period. The partially frozen mixture will not cool until all of the "freezable" water has crystallized; hence, the line CD for pure water occurs at constant temperature. The freezing time is usually defined as the time from the onset of nucleation to the end of the crystal growth phase. After crystallization is completed, the temperature drops from D to E as sensible heat of ice is removed.

During the freezing of the aqueous solution, a freeze-concentration process occurs as water freezes out of solution in the form of pure ice crystals (C'D'), effectively removing solvent from the solute. Hence the freezing temperature of the remaining solution continues to drop. At temperatures well below the initial freezing point, some liquid water remains. Also, a large increase in the viscosity of the unfrozen phase occurs, thus decreasing the diffusion properties of the system and hindering crystallization. It is more difficult to assign a freezing time to this process, but it is usually taken as the time to reach some predetermined temperature below the initial freezing point. This freeze-concentration process establishes the freezing curve

Importance of Crystallization Rate

The freezing curve predicts the amount of ice at any given temperature, which is a function of freezing point depression and hence the number of solutes (concentration of sugar, etc.). It doesn't predict anything about ice crystal size. What predicts ice crystal size is the rate of freezing - the faster the rate - the more nucleation is promoted, and the greater number of crystals of smaller size that will result. This is very important in terms of ice cream structure.

Diagram of a small number of large crystals and a large number of small crystals

Importance of Temperature Fluctuations and Re-Crystallization

Mechanisms of ice recrystallization

Ice crystals formed after scraped-surface freezing and hardening of ice cream are unstable and will undergo recrystallization, the extent of which depends in part on how effectively the system has been stabilized. See also the discussion regarding ice cream shelf-life, where I have included some images to show the effects of recrystallization on ice crystals in ice cream. Recrystallization is the process of changes in number, size and shape of ice crystals during frozen storage, although the amount of ice stays constant with constant temperature throughout this process (dictated by the equilibrium freezing curve). Recrystallization basically involves small crystals disappearing, large crystals growing and crystals fusing together.

There are several types of recrystallization processes. Iso-mass recrystallization ("rounding off") refers to changes in surface or internal structure so that crystals with irregular shapes and large surface-to-volume ratios assume a more compact structure. In other words, sharper surfaces are less stable than flatter ones and will show a tendency to become smoother over time. Migratory recrystallization refers in general to the tendency of larger crystals to grow at the expense of smaller crystals. Ostwald ripening refers to migratory recrystallization that occurs at constant temperature and pressure due to differences in surface energy between crystals, most likely involving melting-diffusion-refreezing or sublimation-diffusion-condensation mechanisms. However, migratory recrystallization is greatly enhanced by temperature fluctuations (heat shock) inducing a melt-refreeze behavior due to ice content fluctuations. Melt-refreeze behavior can lead to complete disappearance of smaller crystals during warming and growth of larger crystals during cooling, or to a decrease in size of crystals during partial melting and regrowth of existing crystals during cooling. Melt-refreeze should occur to a greater extent at higher temperatures and more rapidly for smaller crystals. Accretion refers to a natural tendency of crystals in close proximity to fuse together; the concentration gradients in the areas between them are high, thus, material is transported to the point of contact between crystals and a neck is formed. Further "rounding off" will occur because a high curvature surface like this has a natural tendency to become planar.

Formation of the Glassy Phase in Frozen Foods

During the freezing of foods, ice is formed as pure water goes through the two-step (nucleation and propagation) crystallization process. As temperature decreases and water is removed from a food in the form of ice, the solutes present in the UFP are freeze-concentrated. An equilibrium freezing temperature exists for each ice/UFP ratio, which is a function of the solute concentration. This equilibrium thermodynamic process can be modelled on a phase diagram as an equilibrium freezing (liquidus) curve (see figure below), which extends from the melting temperature (Tm) of pure water (0oC) to the eutectic temperature (Te) of the solute, the point at which the solute has been freeze-concentrated to its saturation concentration.

As temperature is lowered, it is highly unlikely that solute will crystallize at Te, due to high viscosity from concentration of solute and low temperature, so that freeze-concentration proceeds beyond Te in a non-equilibrium state. The highly-concentrated UFP can then go through a viscous liquid/glass state transition, driven by the reduction in molecular motion and diffusion kinetics as a result of both the very high concentration and low temperature.

A glass is defined as a non-equilibrium, metastable, amorphous, disordered solid of extremely high viscosity (ie., 10 exp10 to 10 exp14 Pa.s), also a function of temperature and concentration. The glass transition curve extends from the glass transition temperature (Tg) of pure water (-134oC) to the Tg of pure solute. The equilibrium phase diagram and the kinetically-derived state diagram can be modelled together on a supplemented state diagram. The supplementary state diagram showing the solid/liquid coexistence boundaries and glass transition profile for a binary sucrose/water system is shown in the figure below. Below and to the right of the glass transition line, the solution is in the amorphous glass state, with or without ice present depending on temperature and freezing path followed, while above and to the left of the glass transition line, the solution is in the liquid state, with or without ice depending on temperature.

Graph of glass transition

As an example, assume a sucrose solution with an initial concentration of 20% at room temperature (point A). The initial Tg of this solution at room temperature before phase separation is marked as point B (if the solution could be undercooled to this temperature without ice formation). However, upon slowly cooling of the system somewhat below its equilibrium freezing point (due to undercooling), nucleation and subsequent crystallization begins at point C and initiates the freeze-concentration process, removing water in its pure form as ice. As ice crystallization proceeds, the continual increase in solute concentration (removal of water) further depresses the equilibrium freezing point of the UFP in a manner which follows the liquidus curve (shown as path C) while the Tg of the UFP moves up the glass transition line (path B; due to increased concentration) with a rapid increase in viscosity in a non-Arrhenius manner, particularly in late stages of the freezing process.

Co-crystallization of solute at the Te is unlikely and thus freeze-concentration continues past Te into a non-equilibrium state since the solute becomes superstaurated. When a critical, solute-dependent concentration is reached, the unfrozen liquid exhibits very resisted mobility and the physical state of the UFP changes from a viscoelastic liquid to a brittle, amorphous solid glass.

The intersection of the non-equilibrium extension of the liquidus curve, beyond Te, and the kinetically-determined glass transition curve, point D in the above figure, represents the solute-specific, maximally freeze-concentrated Tg of the frozen system, denoted Tg', where ice formation ceases within the time-scale of the measurement. The corresponding maximum concentrations of water and sucrose "trapped" within the glass at Tg' and unable to crystallize are denoted the Wg' and Cg' , respectively. It is worth noting that this unfrozen water is not bound in an "energetic" sense, rather unable to freeze within practical time frames.

At the Tg', the supersaturated solute takes on solid properties because of reduced molecular motion, which is responsible for the tremendous reduction in translational, not rotational, mobility. It is this intrinsic slowness of molecular reorganization below Tg' that the food technologist seeks to create within the concentrated phase surrounding constituents of food materials.

However, warming from the glassy state to temperatures above the Tg' results in a tremendous increase in diffusion, not only from the effects of the amorphous to viscous liquid transition but also from increased dilution as melting of small ice crystals occurs almost simultaneously (Tg' = Tm'). The time-scale of molecular rearrangement continually changes as the Tg is approached, so that food technologists can also gain some enhanced stability at temperatures above Tg' by minimizing the delta T between the storage temperature and Tg' , either by reduced storage temperatures or enhaced Tg' through freezing methods or formulation. Hence, knowledge of the glass transition provides a clear indication of molecular diffusion and reactivity, and therefore, shelf-stability.

Formation of a Dilute Glass

Despite the thermodynamic driving force to achieve the unfrozen water content corresponding to Wg', one must also consider the large kinetic factors which "overtake" the freezing process. At sub-zero temperatures, the formation of an amorphous state is time-dependent since the limiting factor of the process (water removal in the form of ice) becomes more difficult as concentration increases. The exponential effect of viscosity on mass transfer properties acts as the limiting factor for growth. In addition, under conditions where heat removal is rapid, a high level of undercooling at the interface will only add to a further decrease in propagation rate. The net result is that freezing becomes progressively slower as ice crystallization is hindered and consequently more time is required for lattice growth at each temperature.

Therefore the kinetic restriction imposed on the system can lead to a situation in which non-equilibrium freezing, resulting in a partial dilute glass, can occur. The typical pathway a system may follow during non-equilibrium freezing is shown in the figure on the previous page as the line leading to lower Tg (path E) than Tg' with a corresponding lower sucrose concentration in the glass (Cg) and higher water content in the glass (Wg) due to excess undercooled water plasticized within the glass. This is often referred to as a dilute glass. The magnitude of deviation from the equilibrium curve, and hence the actual path followed, may be regarded as a function of the degree of departure from equilibrium.

Systems possessing this undesirable structure may undergo various relaxation-recrystallization mechanisms in order to maximally freeze-concentrate and minimize the unfrozen water content. As a result, during warming, systems formed under these conditions may lead to one or more low temperature transitions, followed by an exothermic devitrification peak due to crystallization of immobilized water, and finally the onset of ice melting, Tm.

Ice crystallization, recrystallization and glass transitions are active areas of our research here at the University of Guelph. Please see my publications for more details of our research.

Ice Cream Freezing Curves

 Please start with the discussion of the theoretical aspects of freezing to aid in your understanding of the development of the freezing curve.

Graph showing ice cream freezing curve

A good source for calculating initial freezing temperatures and freezing curves of mixes can be found in the following references: 

  • R. Bradley, and K. Smith, Finding the freezing point of frozen desserts, Dairy Record. 84(6): 114 (1983).
  • R. Bradley, Plotting freezing curves for frozen desserts, Dairy Record. 85(7): 86 (1984).

An example calculation can be downloaded here.

 

Ice Cream Shelf-Life

The most frequently occurring textural defect in ice cream is the development of a coarse, icy texture. Iciness is also the primary limitation to the shelf life of ice cream and probably also accounts for countless lost sales through customer dissatisfaction with quality. There is no answer to the question "What is the shelf-life of ice cream?", it depends entirely on its conditions of storage. It might be one year, or it might be two weeks or less. Although the source of and the contributing factors to the problem of icincess are well known, it is also one of the defects about which I am most often asked.

Processor's have known for a long time how to prevent iciness and the answer is still the same: formulate the ice cream properly to begin with, freeze the ice cream quickly in a well-maintained barrel freezer, harden the ice cream rapidly, and avoid as much as possible temperature fluctuations during storage and distribution. Ice crystals need to be numerous and of small, uniform size so they are not detected when eaten. It is heat shock, large temperature fluctuations, which is the greatest culprit to the loss of these small, uniform ice crystal size distributions and resulting coarse, icy texture. Perhaps it is time another message was added to the prevention of iciness and that is to educate the retailer's and the consumer about the causes of iciness and preventative action to maintain a smooth-textured ice cream.

Before we begin looking specifically at shelf-life, you need to re-acquaint yourself with the freezing aspects of ice cream manufacturing, the structure of ice crystals in ice cream, and the theoretical aspects of the freezing process.

Temperature Fluctuations and Ice Recrystallization

Ice crystals are relatively unstable, and during frozen storage, they undergo changes in number, size, and shape, known collectively as recrystallization. This is probably the most important reaction leading to quality losses in all frozen foods. Some recrystallization occurs naturally at constant temperatures, but by far the majority of problems are created as a result of temperature fluctuations. If the temperature during the frozen storage of ice cream increases, some of the ice crystals, particularly the smaller ones, melt and consequently the amount of unfrozen water in the serum phase increases. Conversely, as temperatures decrease, water will refreeze but does not renucleate. Rather, it is deposited on the surface of larger crystals, so the net result is that the total number of crystals diminish and the mean crystal size increases. Temperature fluctuations are common in frozen storage as a result of the cyclic nature of refrigeration systems and the need for automatic defrost. However, mishandling of product is probably the biggest culprit. The sight of ice cream sitting unrefrigerated on a loading dock, in the supermarket aisle, in a shopping cart, or in someone's grocery bag is too common. If one were to track the temperature history of ice cream during distribution, retailing, and finally consumption, one would find a great number of temperature fluctuations. Each time the temperature changes, the ice to serum content changes, and the smaller ice crystals disappear while the larger ones grow even larger. Recrystallization is minimized by maintaining low and constant storage temperatures.

The graph below provides data to show the increase in size of ice crystals that occurs with temperature cycles (from the work of A. Flores and H. D. Goff).

Cumulative distribution of ice crystals in fresh and temperature-cycled ice cream

Below are several cryo-scanning electron micrographic images of ice cream after temperature fluctuations. In the first composite, all pictures are at the same magnification, the top two are fresh, the bottom two are heat-shocked. You can see the tremendous increase in crystals size that has occurred. The next image shows an example of accretion, where crystals fuse as they grow.

cryo-scanning electron micrographic images of ice cream after temperature fluctuations

Example of accretion, where crystals fuse as they grow

The Role of Stabilizers

The ice cream stabilizers, locust bean gum, guar gum, carboxymethyl cellulose, sodium alginate, carrageenan, and xanthan, are a group of ingredients used commonly in ice cream formulations. They are usually integrated with the emulsifiers in proprietary blends. The primary purposes of using stabilizers in ice cream are to produce smoothness in body and texture, retard or reduce ice and lactose crystal growth during storage, and to provide uniformity of product and resistance to melting. Additionally, they stabilize the mix to prevent wheying off, produce a stable foam with easy cut-off at the barrel freezer and slow down moisture migration from the product to the package or the air. The action of the polysaccharides in ice cream result from their ability to form gel-like structures in water and to hold free water. Control of iciness by stabilizers has been attributed to a reduction in the growth of ice crystals over time, probably related to a reduction in water mobility as water is entrapped by their entangled network structures in the serum phase. Proper formulation with stabilizers designed to combat against heat shock is an almost essential defense against the inevitable growth of ice crystals. Low total solids mixes are also more difficult to effectively stabilize as the increased content of water leads to more ice at any given temperature. Also, high concentrations of sugars or lactose will change the ratio of water to ice and lead to greater problems of recrystallization.

Stabilizer functionality in ice cream is an active area of our research here at the University of Guelph. Please see the work of one of my graduate students, Alejandra Regand, in this area, based on her M.Sc. thesis work, which focuses on the structure of polysaccharides in frozen solutions. Please also see my publications for more details of our research.

Education needed

I hope I have stimulated ice cream processors to begin an education campaign for ice cream retailers and consumers about the subject of heat shock and coarseness. I often hear processors say that handling of the product after it leaves their hands is out of their control. Do not forget, however, that the consumer is buying your label of product. The quality they receive is a reflection on you, despite where the damage occurred. The people unloading or stocking your ice cream, and the customer who buys your ice cream cannot be expected to understand the concepts of ice crystal size distributions and ice crystal growth without a little help from you. Ice cream is unlike the other frozen foods they handle routinely and this must be explained to them. We often sell ice cream at the University of Guelph. The majority of our customer's comment on the superb texture of our ice cream. They often ask us what we do differently from other manufacturer's to produce an ice cream that is so smooth. Although we would like to take credit for some great revelation in processing, the difference is that they are buying ice cream that is fresh, directly from our hardening room. If customer's were buying ice cream from the hardening room's of all manufacturer's, no doubt you would get the same comments, but they are not.

That is why I am suggesting some education to retailers and consumers on the subject may be of benefit to both them and you. An information package to retailers on proper handling of ice cream may be very welcome so that they can use it in their training of new and continuing employees. The IICA in Washington has prepared material for this purpose. Consumers can be contacted through side panels on ice cream packages or through point of purchase displays. Whatever the media, the message is that both retailers and consumers can play an important role in maintaining the texture in ice cream which is desired.

Maintaining Shelf-life

  • Formulate the ice cream properly
    • Freezing point depression and sugar considerations
    • Stabilizers
  • Freeze the ice cream quickly in a well-maintained barrel freezer
    • Continuous freezers with high rates of heat exchange
    • Free of fouling (eg., oil) on refrigerant side
    • Blades with a good, even edge
    • Short, insulated process lines through ingredient feeder, packaging equipment
    • Precooling of ingredients
  • Harden the ice cream rapidly
    • High rates of heat transfer: convection (high ΔT and forced air with free air flow) or conduction 
    • Importance of thermal centre and shrink-wrapping of bundles
  • Avoid temperature fluctuations during storage and distribution
    • Importance of low, constant temperatures
    • Avoid mishandling at all stages
  • Educate retailers and consumers about shelf stability
    • Mishandling is usually not at the manufacturing level but quality losses affect consumer acceptance of your product. 

Ice Cream Flavours

Introduction

Most ice cream is purchased by the consumer on basis of flavour and ingredients. There are many different flavours of ice cream manufactured, and to some extent limited only by imagination. Vanilla accounts for 30% of the ice cream consumed. This is partly because it is used in so many products, like milkshakes, sundaes, banana splits, in addition to being consumed with pies, desserts, etc.

It is the ice cream manufacturers responsibility to prepare an excellent mix, but often they put the responsibility of the flavours and ingredients on the supplier.

US Ice Cream Consumption by Flavour, 2010
                                          percentage of volume

1.     Vanilla                                 28.8
2.     Chocolate                            14.3
3.     Bakery/cake/cookie             13.6  
4.     Chocolate chip / other choc   8.6 
5.     All nut flavors                        4.7
6.     Strawberry                             3.3
7.     Neopolitan                             2.5
8.     Coffee                                    1.6
11.   All other flavors                   22.6

Source:  Dairy Facts, 2011, International Dairy Foods Association

Ingredients are added to ice cream in four ways during the manufacturing process:

  1. Mix Tank: for liquid flavours, colours, fruit purees, flavored syrup bases Ð anything that will be homogeneously distributed in the frozen ice cream.
  2. Variegating Pump: for ribbons, swirls, ripples, revels
  3. Ingredient Feeder: for particulates - fruits, nuts, candy pieces, cookies, etc., some complex flavours may utilize 2 feeders
  4. Shaker table: for large inclusions

Generally, the delicate, mild flavours are easily blended and tend not to become objectionable at high concentrations, while harsh flavours are usually objectionable even in low concentrations. Therefore, delicate flavours are preferable to harsh flavours, but in any case a flavour should only be intense enough to be easily recognized. Flavouring materials may be:

  1. Natural
  2. Artificial or imitation
  3. Blends of the two

Vanilla

Vanilla is without exception the most popular flavour for Ice Cream in North America. The dairy industry uses half of the total imported vanilla to North America. It is a very important ice cream ingredient, not only in vanilla ice cream, but in many other flavours where it is used as a flavour enhancer, e.g. chocolate much improved by presence of vanilla.

Vanilla comes from a plant belonging to the orchid family called Vanilla planifolia. There are several varieties of vanilla beans among which are Bourbon, Tahitian, Mexican. Bourbon beans are used to produce best vanilla extracts. Bourbons from Madagescar are the finest and account for over 60% of World production, Indonesia, 23% (UN FAO 2005).

From each blossom of the vine that is successfully fertilized comes a pod which reaches 6-10 inches in length, picked at 6-9 months. It requires 26-29oC day and night throughout the season, and frequent rains with dry season near end for development of flavour.

Pods are immersed in hot water to "kill them" (also increases enzyme activity), then fermented for 3-6 months by repeated wrapping in straw to "sweat" and then uncovered to sun dry. 5-6 kg green pods produce 1 kg. cured pods. Beans then aged 1-2 yrs. Enzymatic reactions produce many compounds - vanillin is the principal flavour compound. However, there is no free vanillin in the beans when they are harvested, it develops gradually during the curing period from glucosides, which break down during the fermentation and "sweating" of the beans. Extraction takes place as the beans are chopped (not ground) and placed in stainless steel percolator and warm alcohol (50oC, 50% solution) is pumped over and through the beans until all flavouring matter is extracted.

Concentrated Extract

Vacuum distillation takes place for a large part of the solvent. The desired concentration is specified as two fold, four fold, etc. Each multiple must be derived from an original 13.35 oz. beans.
Vanilla can be and is produced synthetically to a large extent. By-product of pulp and paper industry (lignan) or petrochemical industry (guaiacol). Compound flavours are produced from combination of vanilla extract and vanillin. Vanillin maybe added at one ounce to the fold and labelled Vanilla-Vanillin Flavour. Number of folds plus number oz. of vanillin equal total strength, eg. 2 fold + 2 oz. = 4 fold vanilla-vanillin. However,more than 1 oz to the fold is deemed imitation.

Vanilla flavouring is available in liquid form as:

  • Natural Vanilla
  • Natural and artificial (reinforced Vanilla with Vanillin)
  • Artificial Vanilla (vanillin)

Usage level in the mix is a function of purity and concentration, usually ~0.3%.

Some vanillin actually improves flavour over pure vanilla extract but too much vanillin results in harsh flavours. 

The choicest of ice creams can be made only with the best of flavouring materials. A good vanilla enhances the flavour of good dairy products in ice cream. It does not mask it.

Chocolate and Cocoa

The cacao bean is the fruit of the tree Theobroma cacao, (Cacao, food of the gods) which grows in tropical regions such as Mexico, Central America, South America, West Indies, African West Coast. The word cocoa is a corruption of the native word cacao. The beans are embedded in pods on the tree, 20-30 beans per pod. When ripe, the pods are cut from the trees, and after drying, the beans are removed from the pods and allowed to ferment, 10 days (microbiological and enzymatic fermentation). Beans then are washed, dried, sorted, graded and shipped.

At the processing plant, beans are roasted, seed coat removed - called the nib. The nib is ground, friction melts the fat and the nibs flow from the grinding as a liquid, known as chocolate liquor.

Liquor:

55% fat, 17% carbohydrate, 11% protein, 6% tannins and many other compounds (bitter chocolate - baking).

Cocoa butter:

fat removed from chocolate liquor, narrow melting range 30 to 36° C

Cocoa:

after the cocoa butter is pressed from the chocolate liquor, the remaining press cake is now material for cocoa manufacture

The amount of fat remaining determines the cocoa grade:

  • medium fat (Breakfast) cocoa 20-24% fat
  • low fat 10-12% fat

Flowchart of how cocoa powder, plain or milk chocolate, and chocolate coated products are made

Cocoa powder can also be alkalized, which reduces acidity/astringency and darkens the colour. Slightly alkalized cocoa is usually preferred in ice cream because it gives a deeper colour but the choice depends upon:

  • consumer preference
  • desired color (Blackshire cocoa may be used to darken color)
  • strength of flavour
  • fat content

There are many types of chocolate that differ in the amounts of chocolate liquor, cocoa butter, sugar, milk, other ingredients, and vanilla.

Imitation chocolate

replacing some or all of the cocoa fat with other vegetable fats. Improved coating properties, resistance to melting

White chocolate

cocoa butter, MSNF, sugar, no cocoa or liquor

In chocolate ice cream manufacture, cocoa is more concentrated for flavouring than chocolate liquor (55% fat) because cocoa butter has relatively low flavour. However, the cocoa fat adds texture to the ice cream. Acceptable mixes can be made using 3% cocoa powder, 2.5% cocoa powder plus 1.5% chocolate liquor, or 5% chocolate liquor.

A good chocolate ice cream will be made if the cocoa and/or chocolate liquor is added to the vat and homogenized with the rest of the mix. Chocolate mixes have a tendency to become excessively viscous sostabilizer content and homogenizing pressure need to be adjusted.

One problem is called chocolate specking. It can occur in soft serve ice cream, when cocoa fibres become entrapped in the churned fat.

Fruit Ice Cream

Fruit for Ice Cream is available in the following forms:

  1. Fresh Fruit
  2. Raw Frozen Fruit
  3. Open Kettle Processed Fruit
  4. Aseptically Processed Fruit

Advantages of processed fruits:

  1. Purchasing year round supply: problems of procurement and storage transferred to fruit processor
  2. Availability: blending of sources from around the world in RTU form, no thawing, straining, etc.
  3. Quality control: processor adjusts for quality variations
  4. Ice Cream quality: fruit won't freeze in ice cream, usually free of debris, straw, pits.
  5. Microbial Safety
  6. Convenience

Fruit feeders are used with continuous freezers to add the fruit pieces, while any fruit juice is added directly to the mix. Fruit is usually added at about 15-25% by weight.

Nuts in Ice Cream

Nuts are usually added at about 10% by wt. Commonly used are walnuts, pecans, filberts, almonds and pistachios. Brazil nuts and cashews have been tried without much success.

Quality Control of Nutmeats for Ice Cream

  1. Extraneous and Foreign Material: Requires extensive cleaning, Colour Sorter, Destoner, X-rays, Aerator, Hand-Picking, Screening
  2. Microbiological Testing: Aflatoxin contamination can be a hazard with Peanuts, Pistachios, Brazils. All nutmeats should receive random testing for: Standard Plate Count, Coliform, E. Coli, Yeast and Mold, Salmonella.
  3. Bacteria Control: Nuts must be processed in a clean sanitary premise following good manufacturing practices. Nuts should be either oil roasted or heat treated to reduce any bacteria.
  4. Sizing: Some nutmeats require chopping to achieve a uniform size in order to fit through the fruit feeder, i.e.: Pecans, Almonds, Peanuts, Filberts
  5. Storage Nutmeats should be stored at 34-38° F to maintain freshness and reduce problems with rancidity.

Colour in Ice Cream

Ice cream should have a delicate, attractive colour that suggests or is closely associated with its flavour. Almost all ice creams are slightly coloured to give them the shade of the natural product 15% fruit produces only a slight effect on colour. However, most suppliers, would include some colour in the fruit to save the processor time i.e. solid pack strawberries include colour. Most colours are of synthetic origin, must be approved, purchased in liquid or dry form. Solutions can easily become contaminated and therefore must be fresh.

Colours are used in ice cream to create appeal. If used to excess they indicate cheapness. The choice of shade is dictated by flavour, i.e. red for strawberry, light green for mint, purple for grape, etc.

Ice Cream Defects

If you haven't already done so, check out the Milk Grading and Defects section for a mini-introduction to the senses. This section will cover the following topics:

Flavour Defects

Can be classified according to the flavouring system (lacks flavour or too high flavour, unnatural flavour), the sweetening system (lacks sweetness or too sweet), processing related flavour defects(cooked), dairy ingredient flavour defects (acid, salty, old ingredient, oxidized/metallic, rancid, or whey flavours), and others (storage/absorbed, stabilizer/emulsifier, foreign). Some details are given below. 

Flavoring System

Unnatural flavor - Caused by using flavours that are not typical of the designated flavour i.e. wintergreen flavour on vanilla ice cream. esp. vanillin

Egg: Caused by using too much egg in an ice cream that is not specified as a custard ice cream - resembles French vanilla ice cream . 

Processing

Cooked: Caused by using milk products heated to too high a temperature or by using excessively high temperatures in mix pasteurization. It can dissipate with time, the same as cooked defect in fluid milk. Sulfhydryl flavor: Caramel-like, scalded milk, oatmeal-like. 

Dairy Ingredients

High Acid: Use of dairy products with high acidity (usually due to bacterial spoilage) or holding mix too long and at too high a temperature before freezing. Acid/sour flavours are more rare these days due to the growth of proteolytic psychrotrophs during storage at elevated temperatures, rather than lactic acid bacteria.

Salty: Ice cream too high in milk solids-not-fat. Too much salt may have been added to the mix. High whey powder, or maybe salted butter used instead of sweet butter.

Old Ingredient: Caused by the use of inferior dairy products in the preparation of the mix. Powders made from poor milk or stored too long at elevated temperature or butter made from poor cream will contribute to old ingredient flavour. Unpleasant aftertaste.

Oxidized: Caused by oxidation of the fat or lipid material such as phospholipid, similar to fluid milk oxidation. Induced by the presence of copper or iron in the mix or from the milk itself. Mono-and-di-glyceride or Polysorbate 80 can also oxidize. Various stages - cardboardy, metallic (also described as painty, fishy).

Rancid: Caused by rancidity (high level of free butyric acid from lipolysis) of milk fat. May be due to use of rancid dairy products (pumping or excessive foaming of raw milk or cream) or to insufficient heat before homogenization of mix. See description of Lipolysis, especially the release of free butyric acid.

Others

Storage: Usually develops from "Lacks Freshness" and is most pronounced on ice cream which have been held in a stale storage atmosphere. Ice cream can also pick up absorbed volatile flavours from the storage environment (e.g., paint, ammonia, or in dipping cabinets - volatiles from nearby flavours.

Body and Texture Defects

1. Coarse/Icy Texture: Due to the presence of ice crystals of such a size that they are noticeable when the ice cream is eaten. See ice cream structure, the freezing aspects of ice cream manufacturingice cream freezing theory, and ice cream shelf life. May be caused by:

  • Insufficient total solids (high water content).
  • Insufficient protein.
  • Insufficient stabilizer or poor stabilizer.
  • Insufficient homogenizing pressure (due to its effect on fat structure formation).
  • Insufficient aging of the mix (stabilizer hydration, also fat crystallization and development of resulting fat structure).
  • Slow freezing because of mechanical condition of freezer.
  • Incorporation of air as large cells because of physical characteristics of mix or type of freezer used.
  • Slow hardening.
  • Fluctuating storage room temperatures.
  • Rehardening soft ice cream.
  • Pumping ice cream too far from continuous freezer before hardening.
  • Fluctuating temperatures during storage and distribution - the most likely cause! See discussion of ice cream shelf life.

2. Crumbly Body: A flaky or snowy characteristic caused by:

  • High overrun together with large air cells.
  • Low stabilizer or emulsifier.
  • Low total solids.
  • Low protein.

3. Fluffy Texture: A spongy/marshmallowy characteristic caused by:

  • Incorporation of large amount of air.
  • Low total solids.
  • Low stabilizer content.

4. Gummy Body: This defect is the opposite of Crumbly in that it imparts a pasty or putty-like body. It is caused by:

  • Too low an overrun.
  • Too much stabilizer.
  • Poor stabilizer.

5. Sandy texture: One of the most objectionable texture defects but easiest to detect. It is caused by Lactose crystals, which do not dissolve readily and produce a rough or gritty sensation in the mouth. This can be distinguished from "iciness" because the lactose crystals do not melt in your mouth. This defect can be prevented by many of the same factors that inhibit iciness:

  • hardening the ice cream quickly
  • maintaining low storage room temps.
  • preventing temperature fluctuations...from manufacturer to consumer

Lactose crystal formation is further discussed in the Dairy Chemistry and Physics section.

6. Weak Body: Ice cream lacks "chewiness" and melts quickly into a watery liquid. Gives impression of lacking richness. May be caused by:

  • Low total solids.
  • High overrun.
  • Insufficient stabilizer.

Melting Quality Characteristics

1. Curdy Melt-Down: May be due to visible fat particles or due to coagulation of the milk proteins so is affected by factors that influence fat destabilization or the protein stability such as:

  • High acidity (protein coagulation).
  • Salt balance (protein coagulation).
  • High homogenizing pressures (fat coagulation).
  • Over-freezing in the freezer (fat coagulation).

2. Does not Melt: See ice cream structure, under the section on melt-down and fat structure/destabilization. May be caused by:

  • Over emulsification.
  • Wrong emulsifier.
  • High fat.
  • Excessive fat clumping in the mix due to homogenization at too low a temperature or single-stage homogenizer.
  • Freezing to too low a temperature at freezer.

3. Wheying off: The salt balance, protein composition, and carrageenan addition (or lack or it) all are factors.

Colour Defects

  1. Colour Uneven: Applies usually to ice cream in which colour has been used, but may be noticed in vanilla ice cream under some circumstances.
  2. Colour Unnatural:
  • Wrong shade of colour used for flavoured ice cream.
  • Too much yellow colouring used in vanilla ice cream.
  • Grayish colour due to neutralization.

Shrinkage

A very troublesome defect in ice cream since there appears to be no single cause or remedy. Defect shows up in hardened ice cream and manifests itself in reduced volume of ice cream in the container usually by pulling away from the top and/or sides of container. Structurally, it is caused by a loss of spherical air bubbles and formation of continuous air channels. Some factors believed associated with the defect are:

  • Freezing and hardening at ultra low temperatures.
  • Storage temperature. Both low and high appear to contribute.
  • Excessive overruns.
  • Pressure changes, for example, from altitude changes (lids popping when shipped to high altitudes, shrinkage when returned to low altitudes).

NOTE: Retailing: More so than other frozen products, ice cream requires constant, uninterrupted freezing cycle at low temperatures to avoid problems. Problems at retail level can arise from overfilling of display cabinet, heat from display lamps or door defrosters, hot air from incorrectly positioned circulation fans, displaying ice cream together with semi-frozen goods.

Homemade Ice Cream

The following information comes from a publication developed by the late Professor A. M. Pearson of the University of Guelph, targeted to the manufacture of ice cream in the home with an old-fashioned hand or electric crank bucket, cooled by ice and salt. There are many other ways to do it, and the recipes are equally applicable. 

Homemade Ice Cream has not lost any of its good, old-fashioned appeal. There is a delicious homemade ice cream to meet every need: regular, low calorie, non-cooked and one using a non-dairy liquid coffee whitener. Everyone can make a homemade ice cream to suit their need with convenience afforded by packages of ingredients from the supermarket.

Janice Bryant
Prof. A.M. Pearson
University of Guelph, 1980

Ice cream fills a useful place in homes throughout the country. It is a favourite for desserts or snacks incorporating an array of many flavour variations. Ice cream contains many nutrients. With the recipes provided, all should be able to enjoy some type of this tempting food. If the regular recipe does not suit your needs, there is the low calorie recipe which contains less than 3% fat for both a cost and calorie saving. The recipe using coffee whitener is significantly less costly than the regular and does not contain milk fat should that be your limitation. So let's mix up a batch of ice cream for anyone and everyone to enjoy!

Ingredients and Recipes Used for Homemade Ice Cream

The main constituents of ice cream are fat, milk solids-not-fat (skim-milk powder), sugar, gelatin (or other suitable stabilizer), egg and flavouring.

A variety of milk products can be used: cream, whole milk, condensed milk and instant skim-milk powder. The recipes stated below proved satisfactory using whipping cream (32-35% fat), table cream (18% fat) and whole milk. The fat gives the product richness, smoothness and flavour. Skim-milk powder is used to increase the solids content of the ice cream and give it more body. It is also an important source of protein which will improve the ice cream nutritionally. Use good quality, fresh powder to avoid imparting a stale flavour to the ice cream.

Liquid coffee whitener (usually purchased frozen) is a cream substitute in one of the recipes. It will yield a slightly different flavour which is still very acceptable. The texture of the ice cream is very creamy. Liquid coffee whitener offers the convenience of being stored frozen in your freezer and is readily available if a quick decision is made to make ice cream.

Sugar is a common ingredient to use as a sweetener. It increases the palatability and improves the body and texture.

The next ingredient, gelatin (or similar substance) assists in absorbing some of the free water in the ice cream mix and helps prevent the formation of large crystals in the ice cream.

It also gives substance or a less watery taste when the ice cream is consumed. The eggs are added to make the fat and water more miscible and also to improve the whipping ability which gives the ice cream greater resistance to melting.

Although vanilla is the flavour added to all of the mixes listed below, you may add flavours to suit you taste.

The yield from the recipes listed below should be three to four litres. 

Regular Vanilla Ice Cream

Table cream 2 litres (2 US quarts)
Instant skim-milk powder 350 ml (1.5 cups)
Sugar 450 ml (2 cups)
Gelatin one 7 g (1/4 oz.) pkg. 
Egg one med or large
Vanilla 10 ml (2 teaspons)
Calories per 100 g 230 

Low Calorie Vanilla Ice Cream

Whole milk 2 litres (2 US quarts)
Instant skim-milk powder 500 ml (2 cups)
Sugar 350 ml (1.5 cups)
Gelatin one 7 g (1/4 oz.) pkg.
Egg one med or large
Vanilla 10 ml (2 teaspons)
Calories per 100 g 125 

Milk Substitute Vanilla Ice Cream

Coffee whitener 2 litres (2 US quarts)
Instant skim-milk powder 350 ml (1.5 cups)
Sugar 500 ml (2 cups)
Gelatin one 7 g (1/4 oz.) pkg.
Egg one med or large
Vanilla 10 ml (2 teaspons)
Calories per 100 g 210

Preparation of the Homemade Ice Cream Mix

The mix (unfrozen ice cream) has to be cooked (pasteurized). For pasteurizing the mix, it is best to use a double boiler to prevent scorching.

Place the liquid ingredients (milk, cream or coffee whitener) in the upper section of the double boiler. Beat in the eggs and the skim-milk powder. Mix the gelatin with the sugar and add to the liquid with constant mixing. While stirring, heat to about 70oC. Place the container in cold water and cool as rapidly as possible to below 18oC.

The ice cream mix is best if it is aged (stored in the refrigerator) overnight. This improves the whipping qualities of the mix and the body and texture of the ice cream. If time does not permit overnight aging, let the mix stand in the refrigerator for at least four hours. After the aging process is completed, remove the mix from the refrigerator and stir in the flavouring.

Freezing the Mix with your Homemade Ice Cream Maker

The freezing procedure has a two-fold purpose, the removal of heat from the mix and the incorporation of air into the mix. Heat is removed by conduction through the metal to the salt water brine surrounding the freezing can. This transfer of heat depends upon the temperature of the brine, the speed of the dasher and how well the dasher scrapes the cold mix from the surface of the freezer can. The dasher speed and surface contact are important to achieve complete removal of the frozen ice cream from the wall of the freezer can. A brine made from 500 grams (1 lb.) of salt and 5 kilograms (11 lbs.) of crushed ice (one pail full) makes a good freezing mixture.

Before starting to freeze the ice cream, make sure all parts of the freezer coming in contact with the ice cream are clean and have been scalded. Let the can cool before pouring in the mix. Place the empty can in the freezer bucket and insert the dasher ensuring both the can and the dasher are centred. Pour the cold, aged mix into the freezer can. The can should not be filled over two-thirds full to allow sufficient room for air incorporation.

The recipes listed below will fill a 5 litre (5 quart U.S.) freezer can to just below the fill line. Attach the motor or crank mechanism, depending on whether your freezer is the electric or hand-cranked style, and latch down securely. Plug in the motor or start turning the crank. Immediately begin adding crushed ice around the can sprinkling it generously with salt. Try to add the salt and ice in the same one to ten proportion to get the proper brine temperature. After the bucket is filled with ice to the overflow hole, pour a little water over the ice to aid in the melting process.

Freeze the mix for 20 to 30 minutes. If the electric motor stalls, immediately unplug it. Remove the motor or crank and take the dasher out of the ice cream. The ice cream will be softly frozen. Scrape the ice cream from the dasher and either scoop into suitable containers or pack in the freezer can. Immediately place the ice cream in the deep freeze to harden.

If freezer facilities are not available, the ice cream can be left in the can, the lid plugged with a cork and placed back into the bucket. Repack the freezer with more ice and salt, cover with a heavy towel and set in a cool place to harden until serving time. This will require further addition of ice and salt depending on the length of time the ice cream is being held. 

Hints for Making Good Homemade Ice Cream

  1.  If the ice cream is very soft, the brine is not cold enough. More salt should be added to reduce the brine temperature.
  2. If the ice cream is coarse and ice in less than 20 minutes, the brine has become to too cold too quickly. Too much salt has been used.
  3. Make the ice cream mix the day before it is frozen to get a smoother product and a higher yield.
  4. Electric freezing takes longer than hand operated.
  5. Use crushed ice for freezing.
  6. Freeze at least 3 hours before the ice cream is to be served.
  7. Be sure dasher is properly centred in the freezer can.
  8. Add liquid flavours before freezing but if you want to add fruits or nuts, add them after freezing and before hardening.
  9. Use a wire whip to blend ingredients for best results.
  10. Clean the salt off all the metal parts of the freezer to prevent corrosion.

For additional recipe suggestions, please see www.ice-cream-recipes.com. Examples of homemade ice cream freezers can be found at country-freezer.com.

Finding Science in Ice Cream - An Experiment for Secondary School Classrooms

This document was designed as a supplement to a classroom experiment for school teachers on ice cream making. 

As the hot weather approaches and students minds begin to drift from the rigors of the school classroom or laboratory, a fun afternoon might be spent making ice cream and in so doing, introducing several aspects of the science and technology "behind the scenes". To suggest that there is no science in ice cream could not be further from the truth. I have made a career out of ice cream research which has taken me into aspects of physical and organic chemistry, microbiology, and chemical engineering to name but a few. Because all of you are from different disciplines and teach in different ways, I will give you enough background information and practice from which you can prepare your own experimental work. You can use the ice cream lab, for example, to demonstrate heat transfer in physics classes, freezing point depression phenomena and emulsions and foams in chemistry classes, or pasteurization and the food use of seaweeds(!) in biology classes. However you use the following information, even if it is for your own family picnic this summer, I hope you enjoy it!

Details of ice cream ingredients, manufacturing, structure, and many other aspects can be found on the side menu.

File attachments: 

Do you suffer from "Ice Cream Headache"?

A lot of people do. From www.howstuffworks.com/question96.htm, "Most people have experienced the dreaded ice cream headache at some point. You are minding your own business on a hot summer day and you are eating something like an ice cream cone, a milk shake, a slurpee or a sno-cone. Then suddenly, out of the blue you are hit with the most excrutiating headache in the world! Fortunately they only last about 30 seconds.

"So where do these horrible headaches come from??? I have not seen a better answer to the question than this excellent article by Joseph Hulihan, Temple University. Here's a summary: When something cold touches the roof of your mouth on a hot day, it triggers a cold headache. The cause is a dilation of blood vessels in the head. The dilation may be caused by a nerve center located above the roof of your mouth - when this nerve center gets cold, it seems to over-react and tries to heat your brain. Therefore, the easy way to avoid brain freeze would be to keep cold things away from the roof of your mouth!"

Further to the research on ice cream headache comes the work of a young school student from Canada.

Ice cream puts Ontario teen in weighty tome

She's only 13 years old but already her research is gracing the pages of a major international medical journal - thanks to ice cream. Maya Kaczorowski of Hamilton has had a study on ice-cream headaches published in the special Christmas double edition of the British Medical Journal, 2002. "I like ice cream and I tend to get ice-cream headaches," Maya said in an interview. But it was the young scientist's curiosity that led to her research. After reading an article about the phenomenon on the medical journal's Web site, she noted that the piece generated many reader responses, some offering remedies and theories about the sensation that results from gobbling down cold treats. It piqued her interest and Maya decided to conduct a random control trial of 145 students at Dalewood Middle School in Hamilton as a project for her science class. With some help from her father, Janusz Kaczorowski, an associate professor with the Department of Family Medicine at McMaster University, the study went off without a hitch.

Half of the children were instructed to eat 100 millilitres of vanilla ice cream in less than five seconds. The other half were told to eat the same amount - the equivalent of about two scoops - so that some was still left in the bowl after 30 seconds. The kids were then told to report whether they developed a headache. The findings suggest that mom is right when she says you should eat ice cream slowly: 27 per cent of students in the "accelerated eating group" reported ice-cream headache, compared with only 13 per cent in the "cautious eating group," the study says. Of the 29 headaches reported, 59 per cent lasted less than 10 seconds. Prof. Kaczorowski said the headache sensation is caused by the ice cream touching the roof of a person's mouth, and that when one eats ice cream quickly, this is more likely to happen than when eating slowly.

The British Medical Journal, published weekly, receives about 6,000 articles submitted for publication each year. For its annual Christmas edition, the journal solicits lighter or unusual material and Prof. Kaczorowski thought his daughter's study fit perfectly. "We submitted the paper at the end of August and we went through the sort of usual peer review and we had to address some of the questions, some of the issues, and then we were told, 'You are in,'" Prof. Kaczorowski said. Maya said she was "really happy" when the study was published and says she "could follow it up with a different type of ice cream, but I'm not sure if I'm going to do that or not." "I have a lot more school work this year," Maya said. She was in Grade 8 when the study was done but has since started high school at Westdale Secondary School in Hamilton. After high school, Maya is thinking of studying to become a university professor, either in sociology or architecture. Here she's following in the footsteps of her father, who has a doctorate degree in sociology.

Public Presentation: "Finding Science in Ice Cream"

an oral presentation to the Royal Canadian Institute for the Advancement of Science, Mississauga, ON, April 4, 2012, which was open to the general public. You can view a 50-minute webcast of this presentation, in which I presented an overview of ice cream manufacture and an overview of the science in ice cream and how that is parlayed into technology and to product quality.

Education and Training Opportunities

 

  • Ice Cream Course in Europe (Ireland): Prof. Goff offers a bienniel 3-day ice cream technology course in Cork, Ireland. The last offering was Feb. 14-16, 2016, the next is planned for Feb. 20-22, 2018.  This will be the eigth offering in a line of very successful courses held in Cork biennially since 2004. This is an excellent opportunity for interested parties from Europe. Details will be available from the Food Industry Training Unit at University College Cork (select "Courses We Offer", then Short Course-Ice Cream Science and Technology). Queries can be sent to Ms. Mary McCarthy-Buckley .

 

  • Ice Cream Course in Australia: Prof. Goff has delivered a series of Ice Cream Science and Technology Courses offered through the Dairy Industry Association of Australia, Melbourne biennially since 2011. The last one in the series was held July 31-Aug. 2, 2017 in Melbourne. Another will be planned for 2019. See the feature article from the Australian Dairy Foods magazine (below) following the 2011 course. 

 

  • Professor Goff is available for proprietary on-site training programs of various length specific to your needs. Please email me to discuss.

 

 

Reference Book Now Available: Ice Cream, 7th Edition

Goff, H. Douglas, Hartel, Richard W.

7th ed. 2013, Hardcover, 462 p. 129 illus., 75 in color.

ISBN 978-1-4614-6095-4

Details and order information available at http://www.springer.com/food+science/book/978-1-4614-6095-4

Ice Cream, 7th Edition focuses on the science and technology of frozen dessert production and quality. It explores the entire scope of the ice cream and frozen dessert industry, from the chemical, physical, engineering and biological principles of the production process to the distribution of the finished product. It is intended for industry personnel from large to small scale processors and suppliers to the industry and for teachers and students in dairy or food science or related disciplines. While it is technical in scope, it also covers much practical knowledge useful to anyone with an interest in frozen dessert production. World-wide production and consumption data, global regulations and, as appropriate, both SI and US units are provided, so as to ensure its relevance to the global frozen dessert industry.

This edition has been completely revised from the previous edition, updating technical information on ingredients and equipment and providing the latest research results. Two new chapters on ice cream structure and shelf-life have been added, and much material has been rearranged to improve its presentation. Outstanding in its breadth, depth and coherence, Ice Cream, 7th Edition continues its long tradition as the definitive and authoritative resource for ice cream and frozen dessert producers.

H. Douglas Goff is a Professor of Food Science at the University of Guelph, Canada. He has been teaching and conducting research in ice cream science and technology for more than 30 years. 

Richard W. Hartel is a Professor of Food Engineering in the Department of Food Science at the University of Wisconsin-Madison, USA.  He has over 20 years of experience working on the structural attributes of ice cream.

 Download the book flyer from Springer here.