Dairy Products

Overview and Fluid Milk Products

Overview of the Range of Products that can be Manufactured from Milk as a Starting Point

Diary Tree showing the range of products that can be manufactured from milk

Fluid Milk Products and Processing

Beverage Milks

The production of beverage milks combines the unit operations of clarification, separation (for the production of lower fat milks), pasteurization, and homogenization. The process is simple, as indicated in the flow chart. While the fat content of most raw milk is 4% or higher, the fat content in most beverage milks has been reduced to 3.4%. Lower fat alternatives, such as 2% fat, 1% fat, or skim milk (<0.1% fat) or also available in most markets. These products are either produced by partially skimming the whole milk, or by completely skimming it and then adding an appropriate amount of cream back to achieve the desired final fat content.

Vitamins may be added to both full fat and reduced fat milks. Vitamins A and D (the fat soluble ones) are often supplemented in the form of a water soluble emulsion to offset that quantity lost in the fat separation process.

Diagram of the process of clarification, separation, pasteurization, and homogenization for producing milk

Creams

During the separation of whole milk, two streams are produced: the fat-depleted stream, which produces the beverage milks as described above or skim milk for evaporation and possibly for subsequent drying, and the fat-rich stream, the cream. This usually comes off the separator with fat contents in the 35-45% range. Cream is used for further processing in the dairy industry for the production of ice cream or butter, or can be sold to other food processing industries. These industrial products normally have higher fat contents than creams for retail sale, normally in the range of 45-50% fat. A product known as "plastic" cream can be produced from certain types of milk separators. This product has a fat content approaching 80% fat, but it remains as an oil-in-water emulsion (the fat is still in the form of globules and the skim milk is the continuous phase of the emulsion), unlike butter which also has a fat content of 80% but which has been churned so that the fat occupies the continuous phase and the skim milk is dispersed throughout in the form of tiny droplets (a water-in-oil emulsion).

For retail cream products, the fat is normally standardized to 35% (heavy cream for whipping), 18% or 10% (cream for coffee or cereal). Higher fat creams have also been produced for retail sale, a product known as double cream has a fat content of 55% and is quite thick. Creams for packaging and sale in the retail market must be pasteurized to ensure freedom from pathogenic bacteria. Whipping cream is not normally homogenized, as the high fat content will lead to extensive fat globule aggregation and clustering, which leads to excessive viscosity and a loss of whipping ability. This phenomena has been used, however, to produce a spoonable cream product to be used as a dessert topping. Lower fat creams (10% or 18%) can be homogenized, usually at lower pressure than whole milk.

Whipped Cream Structure

The structure of whipped cream is very similar to the fat and air structure that exists in ice cream. Cream is an emulsion with a fat content of 35-40%. When you whip a bowl of heavy cream, the agitation and the air bubbles that are added cause the fat globules to begin to partially coalesce in chains and clusters and adsorb to and spread around the air bubbles.

Diagram of whipped cream structureAs the fat partially coalesces, it causes one fat-stabilized air bubble to be linked to the next, and so on. The whipped cream 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. The water, lactose and proteins are trapped in the spaces around the fat-stabilized air bubbles. The crystalline fat content is essential (hence whipping of cream is very temperature dependent) so that the fat globules partially coalesce into a 3-dimensional structure rather than fully coalesce into larger and larger globules that are not capable of structure-building. This is caused by the crystals within the globules that cause them to stick together into chains and clusters, but still retain the individual identity of the globules. Please see a further description of this process for details. If whipped cream is whipped too far, the fat will begin to churn and butter particles will form.

Partially-crystalline Fat Globule, Partially-coalesced

Below are scanning electron micrographs image of whipped cream. If you compare the schematics above with the "real thing" below, you should be able to fully understand whipped cream structure.

The structure of whipped cream as determined by scanning electron microscopy. A. Overview showing the relative size and prevalence of air bubbles (a) and fat globules (f); bar = 30 um. B. Internal structure of the air bubble, showing the layer of partially coalesced fat which has stabilized the bubble; bar = 5 um. C. Details of the partially coalesced fat layer, showing the interaction of the individual fat globules. Bar = 3 um. 

The structure of whipped cream as determined by scanning electron microscopyFat partial coalescence as it affects things like whipped cream and 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.

Recombined Milk

Beverage milks can also be prepared by recombining skim milk powder and butter with water. This is often done in countries where there is not enough milk production to meet the demand for beverage milk consumption. The concept is simple. Skim milk powder is dispersed in water and allowed to hydrate. Butter is then emulsified into this mixture by either blending melted butter into the liquid mixture while hot, or by dispersing solid butter into the liquid through a high shear blender device. In some cases, a non-dairy fat source may also be used. The recombined milk product is then pasteurized, homogenized and packaged as in regular milk production. The final composition is similar to that of whole milk, approximately 9% milk solids-not-fat, and either 2% or 3.4% fat. The water source must be of excellent quality. The milk powder used for recombining must be of high quality and good flavour. Care must be taken to ensure adequate blending of the ingredients to prevent aggregation or lumping of the powder. Its dispersal in water is the key to success.

Chocolate Milk

An industry standard for the production of chocolate milk consists of:

  • 93% milk
  • 6.3% sugar
  • 0.65% cocoa powder
  • 0.05% carrageenan

The final product is usually standardized to either 2% fat or 1% fat (meaning, 2.15% or 1.1% fat in the milk before addition of other ingredients). The sugar, cocoa powder and carrageenan are dry blended, and added to cold milk with vigorous agitation, and then pasteurized.

Concentrated and Dried Dairy Products

Fluid milk contains approximately 88% water. Concentrated milk products are obtained through partial water removal. Dried dairy products have even greater amounts of water removed to usually less than 4%. The benefits of both these processes include an increased shelf-life, convenience, product flexibility, decreased transportation costs, and storage.

The following products will be discussed here:

Concentrated Dairy Products

  • Evaporated Skim or Whole Milk
  • Sweetened Condensed Milk
  • Condensed Buttermilk
  • Condensed Whey

Dried Dairy Products

  • Milk Powder
  • Whey Powder
  • Whey Protein Concentrates

The principles of evaporation and dehydration can be found in the Dairy Processing section.

Concentrated Dairy Products

Evaporated Skim or Whole Milk

After the raw milk is clarified and standardized, it is given a pre-heating treatment of 93-100° C for 10 to 25 min or 115-128° C for 1 to 6 min.. There are several benefits to this treatment:

  • increases the concentrated milk stability during sterilization; decreases the chance of coagulation taking place during storage
  • decreases the initial microbial load
  • modifies the viscosity of the final product
  • milk enters the evaporator already hot

Milk is then concentrated at low temperatures by vacuum evaporation. This process is based on the physical law that the boiling point of a liquid is lowered when the liquid is exposed to a pressure below atmospheric pressure. In this case, the boiling point is lowered to approximately 40-45° C. This results in little to no cooked flavour. The milk is concentrated to 30-40% total solids.

The evaporated milk is then homogenized to improve the milkfat emulsion stability. There are other benefits particular to this type of product:

  • increased white colour
  • increased viscosity
  • decreased coagulation ability

A second standardization is done at this time to ensure the proper salt balance is present. The ability of milk to withstand intensive heat treatment depends to a great degree on its salt balance.

The product at this point is quite perishable. The fat is easily oxidized and the microbial load, although decreased, is still a threat. The evaporated milk at this stage is often shipped by the tanker for use in other products.

In order to extend the shelf life, evaporated milk can be packaged in cans and then sterilized in an autoclave. Continuous flow sterilization followed by packaging under aseptic conditions is also done. While the sterilization process produces a light brown colouration, the product can be successfully stored for up to a year.

Sweetened Condensed Milk

Where evaporated milk uses sterilization to extend its shelf-life, sweetened condensed milk has an extended shelf-life due to the addition of sugar. Sucrose, in the form of crystals or solution, increases the osmotic pressure of the liquid. This in turn, prevents the growth of microorganisms.

The only real heat treatment (85-90° C for several seconds) this product receives is after the raw milk has been clarified and standardized. The benefits of this treatment include totally destroying osmophilic and thermophilic microorganisms, inactivating lipases and proteases, decreases fat separation and inhibits oxidative changes. Unfortunately it also affects the final product viscosity and may promote the defect age gelation.

The milk is evaporated in a manner similar to the evaporated milk. Although sugar may be added before evaporation, post evaporation addition is recommended to avoid undesirable viscosity changes during storage. Enough sugar is added so that the final concentration of sugar is approximately 45%.

The sweetened evaporated milk is then cooled and lactose crystallization is induced. The milk is inoculated, or seeded, with powdered lactose crystals, then rapidly cooled while being agitated. The lactose can crystalize without the seeding but there is the danger of forming crystals that are too large. This would result in a texture defect similar in ice cream called sandiness, which affects the mouthfeel. By seeding, the number of crystals increases and the size of those crystals decreases.

The product is packaged in smaller containers, such as cans, for retail sales and bulk containers for industrial sales.

Condensed Buttermilk

Buttermilk is a by-product of the butter industry. It can be evaporated on its own or it can be blended with skimmilk and dried to produce skimmilk powder. This blended product may oxidise readily due to the higher fat content. Condensed buttermilk is perishable and, therefore, the supply must be fresh and it must be stored cool.

Condensed Whey

In the process of cheesemaking, there is a lot of whey that needs to be disposed of. One of the ways of utilizing cheese whey is to condense it. The whey contains fat, lactose, ß -lactoglobulin, alpha-lactalbumin, and water. The fat is generally removed by centrifugation and churned as whey cream or used in ice cream. Evaporation is the first step in producing whey powder.

Dried Dairy Products

Milk Powder

Milk used in the production of milk powders is first clarified, standardized and then given a heat treatment. This heat treatment is usually more severe than that required for pasteurization. Besides destroying all the pathogenic and most of the spoilage microorganisms, it also inactivates the enzyme lipase which could cause lipolysis during storage.

The milk is then evaporated prior to drying for the following reasons:

  • less occluded air and longer shelf life for the powder
  • viscosity increase leads to larger powder particles
  • less energy required to remove part of water by evaporation; more economical

Homogenization may be applied to decrease the free fat content. Spray drying is the most used method for producing milk powders. After drying, the powder must be packaged in containers able to provide protection from moisture, air, light, etc. Whole milk powder can then be stored for long periods (up to about 6 months) of time at ambient temperatures.

Skim milk powder (SMP) processing is similar to that described above except for the following points:

  1. contains less milkfat (0.05-0.10%)
  2. heat treatment prior to evaporation can be more or less severe
  3. homogenization not required
  4. maximum shelf life extended to approximately 3 years

Low-heat SMP is given a pasteurization heat treatment and is used in the production of cheese, baby foods etc. High-heat SMP requires a more intense heat treatment in addition to pasteurization. This product is used in the bakery industry, chocolate industry, and other foods where a high degree of protein denaturation is required.

Instant milk powder is produced by partially rehydrating the dried milk powder particles causing them to become sticky and agglomerate. The water is then removed by drying resulting in an increased amount of air incorporated between the powder particles.

Whey Powder

Whey is the by-product in the manufacturing of cheese and casein. Disposing of this whey has long been a problem. For environmental reasons it cannot be discharged into lakes and rivers; for economical reasons it is not desirable to simply dump it to waste treatment facilities. Converting whey into powder has led to a number products that it can be incorporated into. It is most desirable, if and where possible, to use it for human food, as it contains a small but valuable protein component. It is also feasible to use it as animal feed. Between the pet food industry and animal feed mixers, hundred's of millions of pounds are sold every year. The feed industry may be the largest consumer of dried whey and whey products.

Whey powder is essentially produced by the same method as other milk powders. Reverse osmosis can be used to partially concentrate the whey prior to vacuum evaporation. Before the whey concentrate is spray dried, lactose crystallization is induced to decrease the hygroscopicity. This is accomplished by quick cooling in flash coolers after evaporation. Crystallization continues in agitated tanks for 4 to 24 h.

fluidized bed may be used to produce large agglomerated particles with free-flowing, non-hygroscopic, no caking characteristics.

Whey Protein Concentrates

Both whey disposal problems and high-quality animal protein shortages have increased world-wide interest in whey protein concentrates. After clarification and pasteurization, the whey is cooled and held to stabilize the calcium phosphate complex, which later decreases membrane fouling. The whey is commonly processed using ultrafiltration, although reverse osmosis, microfiltration, and demineralization methods can be used. During ultrafiltration, the low molecular weight compounds such as lactose, minerals, vitamins and nonprotein nitrogen are removed in the permeate while the proteins become concentrated in the retentate. After ultrafiltration, the retentate is pasteurized, may be evaporated, then dried. Drying, usually spray drying, is done at lower temperatures than for milk in order that large amounts of protein denaturation may be avoided.

Cultured Dairy Products and Cheese

Cheese - the short version

Traditionally, cheese was made as a way of preserving the nutrients of milk. In a simple definition, cheese is the fresh or ripened product obtained after coagulation and whey separation of milk, cream or partly skimmed milk, buttermilk or a mixture of these products. It is essentially the product of selective concentration of milk. Thousands of varieties of cheeses have evolved that are characteristic of various regions of the world.

Some common cheesemaking steps will be outlined here. Also included is a document entitled "Making Cheese at Home", which includes some helpful references, several simple cheese making procedures and information about sourcing cheese making supplies.

Please refer to the extended version, Cheese Making Technology, for further details.

Treatment of Milk for Cheesemaking

Like most dairy products, cheesemilk must first be clarifiedseparated and standardized. The milk may then be subjected to a sub-pasteurization treatment of 63-65° C for 15 to 16 sec. This thermization treatment results in a reduction of high initial bacteria counts before storage. It must be followed by proper pasteurization. While HTST pasteurization (72° C for 16 sec) is often used, an alternative heat treatment of 60° C for 16 sec may also be used. This less severe heat treatment is thought to result in a better final flavour cheese by preserving some of the natural flora. If used, the cheese must be stored for 60 days prior to sale, which is similar to the regulations for raw milk cheese.

Homogenization is not usually done for most cheesemilk. It disrupts the fat globules and increases the fat surface area where casein particles adsorb. This reults in a soft, weak curd at renneting and increased hydrolytic rancidity.

Additives

The following may all be added to the cheese milk:

  • Calcium chloride
  • nitrates
  • colour
  • hydrogen peroxide
  • lipases

Calcium chloride is added to replace calcium redistributed during pasteurization. Milk coagulation by rennet during cheese making requires an optimum balance among ionic calcium and both soluble insoluble calcium phosphate salts. Because calcium phosphates have reverse solubility with respect to temperature, the heat treatment from pasteurization causes the equilibrium to shift towards insoluble forms and depletes both soluble calcium phosphates and ionic calcium. Near normal equilibrium is restored during 24 - 48 hours of cold storage, but cheese makers can't wait that long, so CaCl2 is added to restore ionic calcium and improve rennetability. The calcium assists in coagulation and reduces the amount of rennet required.

Sodium or potassium nitrate is added to the milk to control the undesirable effects of Clostridium tyrobutyricum in cheeses such as Edam, Gouda, and Swiss.

Because milk colour varies from season to season, colour may added to standardize the colour of the cheese throughout the year. Annato, Beta-carotene, and paprika are used.

The addition of hydrogen peroxide is sometimes used as an alternative treatment for full pasteurization.

Lipases, normally present in raw milk, are inactivated during pasteurization. The addition of kid goat lipases are common to ensure proper flavour development through fat hydrolysis.

Inoculation and Milk Ripening

The basis of cheesemaking relies on the fermentation of lactose by lactic acid bacteria (LAB). LAB produce lactic acid which lowers the pH and in turn assists coagulation, promotes syneresis, helps prevent spoilage and pathogenic bacteria from growing, contributes to cheese texture, flavour and keeping quality. LAB also produce growth factors which encourages the growth of non-starter organisms, and provides lipases and proteases necessary for flavour development during curing. Further information on LAB and starter cultures can be found in the microbiology section.

After innoculation with the starter culture, the milk is held for 45 to 60 min at 25 to 30° C to ensure the bacteria are active, growing and have developed acidity. This stage is called ripening the milk and is done prior to renneting.

Milk Coagulation

Coagulation is essentially the formation of a gel by destabilizing the casein micelles causing them to aggregate and form a network which partially immobilizes the water and traps the fat globules in the newly formed matrix. This may be accomplished with:

  • enzymes
  • acid treatment
  • heat-acid treatment

Enzymes

Chymosin, or rennet, is most often used for enzyme coagulation.

Acid Treatment

Lowering the pH of the milk results in casein micelle destabilization or aggregation. Acid curd is more fragile than rennet curd due to the loss of calcium. Acid coagulation can be achieved naturally with the starter culture, or artificially with the addition of gluconodeltalactone. Acid coagulated fresh cheeses may include Cottage cheese, Quark, and Cream cheese.

Heat-Acid Treatment

Heat causes denaturation of the whey proteins. The denatured proteins then interact with the caseins. With the addition of acid, the caseins precipitate with the whey proteins. In rennet coagulation, only 76-78% of the protein is recovered, while in heat-acid coagulation, 90% of protein can be recovered. Examples of cheeses made by this method include Paneer, Ricotta and Queso Blanco.

Curd Treatment

After the milk has gel has been allowed to reach the desired firmness, it is carefully cut into small pieces with knife blades or wires. This shortens the distance and increases the available area for whey to be released. The curd pieces immediately begin to shrink and expel the greenish liquid called whey. This syneresis process is further driven by a cooking stage. The increase in temperature causes the protein matrix to shrink due to increased hydrophobic interactions, and also increases the rate of fermentation of lactose to lactic acid. The increased acidity also contributes to shrinkage of the curd particles. The final moisture content is dependant on the time and temperature of the cook stage. This is important to monitor carefully because the final moisture content of the curd determines the residual amount of fermentable lactose and thus the final pH of the cheese after curing.

When the curds have reached the desired moisture and acidity they are separated from the whey. The whey may be removed from the top or drained by gravity. The curd-whey mixture may also be placed in moulds for draining. Some cheese varieties, such as Colby, Gouda, and Brine Brick include a curd washing which increases the moisture content, reduces the lactose content and final acidity, decreases firmness, and increases openness of texture.

Curd handling from this point on is very specific for each cheese variety. Salting may be achieved through brine as with Gouda, surface salt as with Feta, or vat salt as with Cheddar. To achieve the characteristics of Cheddar, a cheddaring stage (curd manipulation), milling (cut into shreds), and pressing at high pressure are crucial.

Cheese Ripening

Except for fresh cheese, the curd is ripened, or matured, at various temperatures and times until the characteristic flavour, body and texture profile is achieved. During ripening, degradation of lactose, proteins and fat are carried out by ripening agents. The ripening agents in cheese are:

  • bacteria and enzymes of the milk
  • lactic culture
  • rennet
  • lipases
  • added moulds or yeasts
  • environmental contaminants

Thus the microbiological content of the curd, the biochemical composition of the curd, as well as temperature and humidity affect the final product. This final stage varies from weeks to years according to the cheese variety.

Making Cheese at Home

by Dr. A.R. Hill

Department of Food Science

University of Guelph, ON N1G 2W1

Email: Dr. A.R. Hill

Cheese is made from the milk of goats, sheep, buffalo, reindeer, camel, llama, and yak but is usually made from cow's milk. Cow's milk is about 88% water and the remainder is fat, protein, sugar, minerals and vitamins. In the process of cheese-making, most of the protein, fat and some minerals and vitamins are concentrated and separated as a solid. The remaining liquid, called 'whey', contains most of the sugar and water and some protein, minerals and vitamins. Whey is utilized in foods and feeds or disposed of as waste.

There are two principal agents which bring about the concentration and separation of protein and fat to make cheese, namely, bacterial culture and coagulating enzyme.

Bacterial culture

Bacteria are often responsible for food spoilage but there are also many useful types. During the manufacture of cheese and other cultured dairy products lactic acid bacteria change the milk sugar to lactic acid. The acid acts as a preservative by inhibiting undesirable types of bacteria, helps remove water from the curd (formation of curd is described in the next section) and is important to the development of cheese texture. The lactic acid bacteria and other microorganisms which happen to be present in the cheese contribute enzymes which break down fats, proteins and sugar during aging to produce flavours characteristic of particular cheese varieties. Lactic acid bacteria are naturally present in milk, and cheese can be made by holding fresh milk in a warm environment. However, this process is slow and cheese quality tends to be inconsistent. It is recommended that the milk be pasteurized by heating at 60-62C (140-144F) for 30 min . This heat treatment will destroy most lactic acid bacteria in the milk and will also destroy pathogenic bacteria which may cause food illness. Note that over pasteurization will prevent proper coagulation. Most store bought milk is unsuitable for cheese making because it has received too much heat treatment.

After pasteurization the milk is cooled to 32-37C (89.6-98.6F) and lactic acid bacteria are added to the milk. The suspension of bacteria is called a 'culture' and the process of adding the culture to the milk is called 'inoculation'. The culture may be a frozen or freeze-dried concentrate of bacterial cells or it could be cultured milk (milk in which lactic acid bacteria have been allowed to grow). Different bacterial cultures are recommended for specific types of cheese but most types can be made using fresh, plain yoghurt or buttermilk as a culture. If yoghurt is used, the milk should be inoculated at 37C. Buttermilk contains gas forming bacteria and may cause the development of small eyes in some cheese. In addition to bacteria, some types of cheese such as 'blue' and 'camembert' are inoculated with mould to develop characteristic appearance and flavour. 

Coagulating enzymes 

Proteins can be thought of as long microscopic chains. Various food products such as jello, jams and cheese depend on the ability of protein chains to intertwine and form a mesh-like network. The formation of this network is called 'coagulation'. When proteins coagulate in water, they trap water in the network and change the liquid to a semisolid gel. In cheese-making gelation is caused by an enzyme, 'rennet'. When rennet is added to warm milk, the liquid milk is transformed into a soft gel. When the gel is firm enough, it is cut into small pieces, 0.5-1.0 cm square (1/4-3/8 inch) called 'curds'. 

 Exceptions

Certain types of cheese such as some types of Queso Blanco (Latin American countries) and Paneer (India) are made without bacterial cultures and without rennet. In these types, curd is formed by adding vinegar (or other acid juices) to hot milk. A procedure for heat-acid precipitated Queso Blanco is included in this booklet because it is one of the most simple varieties to make and has the advantage that all the milk proteins including proteins normally lost in the whey are included in the cheese. Some fresh cheese (i.e. cheese which are eaten immediately after manufacture) such as Cottage cheese and quark are made with little or no rennet. In these cheese, coagulation is caused by high acid development by the bacterial culture. A procedure for fresh cheese or European style Cottage cheese is included.

Cheese-making supplies and training

For the home cheese maker, a start up set of supplies should include: a pasteuriser, cheese mould, cheese press, dairy thermometer or any food grade thermometer for the range of 0 to 100C, and cheese cloth. Bacterial cultures and rennet can sometimes be purchased in natural food stores.

Small scale cheese making equipment and other supplies, including literature, can be obtained from New England Cheese Making Supply Company, 85 Main St., Ashfield, MA 01330 (413-628-3808; Fax: 413-628-4061).

Cheese making supplies and one day courses in cheese making are available from Glengarry Cheesemaking and Dairy Supplies, RR#2,Alexandria, Ontario, K0C 1A0 Phone: (613) 525-3133, Fax: (613) 525-3394, glengarrycheesemaking.on.ca

Cultures, rennet, cheesemaking equipment and other supplies are available from Danlac, 466 Summerwood Place, Airdrie, Alberta, T4B 1W5, Phone 403-948-4644, Fax 403-948-4643, www.danlac.com, e-mail Egon Skovmose

Freeze dried cultures and rennet in tablet form are available in large orders from Chr. Hansens Laboratories Ltd., 1146 Aerowood Drive, Mississauga, L4N 1Y5, 905-625-8157, and from Rhodia Canada Inc., 2000 Argentia Road, Plaza 3, Suite 400, Mississauga, Ontario, L5N 1V9, Phone 905-821-4450, Fax 905-821-9339. Call and ask about retail distributors closest to you.

Some References

 Alfa-Laval. Dairy Handbook. Alfa-Laval, Food Engineering AB. P.O. Box 65, S-221 00 Lund, Sweden. [Well illustrated text. Excellent introduction to dairy technology].

American Public Health Association, Standard Methods for the examination of dairy products. 1015 Eighteenth St. NW, Washington, D.C.

Berger, W., Klostermeyer, H., Merkenich, K. and Uhlmann, G. 1989. Processed Cheese Manufacture, A JOHA guide. BK Ladenburg, Ladenburg.

Carroll, R. and Carroll, R. 1982. Cheese making made easy. Storey Communications Inc., Ponnal, Vermont. [Well illustrated manual for small and home cheese making operations]

Kosikowski, F.V. and Mistry, V.V. 1997. Cheese and Fermented Milk Foods, 3rd Edition, F.V. Kosikowski and Associates, Brooktondale, NY.

Law, B. 1999. Technology of cheese making Sheffield Academic Press, Sheffield, UK.

Scott, R., Robinson, R.K. and Wilbey, R.A. 1998. Cheese making Practice. 3rd Edition. Applied Science. Publ. Ltd., London.

Troller, J.A. 1993. Sanitation in Food Processing. 2nd Edition. Academic Press. New York.

Walstra, P., Geurts, T.J., Noomen, A., Jellema, A. and van Boekel, M.A.. 1999. Dairy Technology. Marcel Dekker Inc. New York, NY. 

Websites  

Food Science University of Guelph: http://www.uoguelph.ca/foodscience/content/dairy-education-series

Centre For Dairy Research, Madison, WI. www.cdr.wisc.edu/

Canadian Dairy Information Centre, www.dairyinfo.gc.ca

CheeseNet , cheesenet.wgx.com/

 

SWEET CURD BRICK CHEESE

 Brick cheese is a semi-soft ripened cheese. Its texture and flavour is derived from the action of bacteria which grow on the surface of the cheese. It is usually formed in the shape of a loaf.

Procedure  

  1. Pasteurize whole milk by heating at 62C for 30 min. Do not over pasteurize.
  2. Cool milk to 30C and add 25 ml of low temperature (sometimes called mesophyllic cheese starter and 2 ml of rennet per 10 kg of milk. (Note: a bacterial smear should develop spontaneously during ripening in the wet room (Step 12), however, you can increase the success rate and uniformity by adding a smear culture with the lactic culture. Suitable cultures are available from many culture suppliers)
  3. When the milk gel breaks cleanly on a knife (about 25 minutes after adding rennet), cut the gel into 1/4" cubes.
  4. Stir gently for 10 minutes.
  5. Begin cooking. Slowly raise the temperature to 36C. This should take 20 minutes.
  6. Remove most of the whey but leave enough to cover the curd.
  7. Add water at 36C to wash the curd. Add the equivalent of half the weight of the milk and agitate gently for 20 minutes.
  8. Drain most of the whey but leave enough to cover the curd.
  9. Pour the curd and remaining wash water into the hoops.
  10. Turn the cheese after the first 30 minutes and then every hour for 4 hours (5 turns in all).
  11. Rub salt over the entire surface of the cheese.
  12. Store cheese in a wet room (95% humidity) at 12-15C to develop a smear (bacterial growth on surface) for about 2 weeks. Turn the cheese every second or third day and wash with 4% brine. In the absence of a wet room you can put the cheese in a covered but not sealed container. The interior must remain moist and have some air exchange.
  13. Wash cheese to remove smear, dry and vacuum package or coat with paraffin. Store at 5C for further ripening. Flavour should be optimum after about 4 weeks of ripening.

  

EUROPEAN STYLE COTTAGE CHEESE

European style cottage cheese has small curds and is often heavily creamed. The milk is coagulated by a lactic culture without rennet or other coagulating enzyme. 

Procedure   

  1. Skim as much cream as possible from fresh milk.
  2. Pasteurize the skim milk at 62C for 30 minutes and the cream at 70C for 30 minutes.
  3. Cool the skim milk to 32C.
  4. Add a low temperature cheese starter at the rate of 5%, i.e. 0.5 kg starter for every 10 kg of milk. Let milk set for 4-6 hours until a soft gel is formed. When broken with a knife or a blunt object the curd should break cleanly and the broken portion should fill up with clear whey. Alternatively, 1% of culture may be used with a setting time of 12-18 hours.
  5. Stir gently and heat slowly to 52C. Hold at this temperature until curd is firm, about 30 minutes.
  6. Drain most of the whey, replace it with cold water and agitate gently for 15 minutes to leach the acid flavour from the curd. Washing may be omitted if you prefer an acid cheese.
  7. Drain the remaining whey and wash water.
  8. Add cream or cream dressing to the curd according to taste.  

 Note: It may be convenient to drain the curd in a cloth bag, in which case, it could be washed by soaking the whole bag in cold water for 15 minutes.

 

NO-RENNET QUESO BLANCO (LATIN AMERICAN WHITE CHEESE)

Heat-acid or no-rennet Queso Blanco is a white, semi-hard cheese made without culture or rennet. It is eaten fresh and may be flavoured with peppers, caraway, onions, etc. It belongs to a family of "frying cheeses" which do not melt and may be deep fried or barbecued to a golden brown for a tasty snack. Deep fried Queso Blanco may be steeped in a sugar syrup for a dessert dish or added to soup as croutons. The procedure given here is similar to the manufacture of Indian Paneer and Channa which is made by adding acid to hot milk. Ricotta cheese is also made by heat-acid precipitation of proteins from blends of milk and whey. Latin American white cheese is also made by renneting whole milk with little or no bacterial culture. Rennet Queso Blanco is also useful as a frying cheese because its lack of acidity gives it low meltability.

Procedure  

  1. Heat milk to 80C for 20 minutes.
  2. Add vinegar (5% acetic acid) at the rate of about 175 ml per 5 kg of milk. Vinegar should be diluted in two equal volumes of water and then added slowly to the hot milk until the whey is semi-clear and the curd particles begin to mat together and become slightly stretchy. You should be able to stretch a piece of curd about 1 cm before it breaks. It may not be necessary to add all of the vinegar.
  3. Separate the curd by filtering through a cloth bag until free whey is removed.
  4. Work in salt (about 1%) and spices to taste.
  5. Press the curd (high pressure is not required).
  6. Package curd in boilable bags (vacuum package if possible) and place in boiling water for 5 minutes to sterilize the surface and prevent mould growth.
  7. Queso Blanco may keep for several weeks if properly packed but should be eaten as fresh as possible.

 

RICOTTA CHEESE RECIPE

  1. Heat fresh whey to 85C. Heating must begin immediately after the whey is removed from the curd to prevent further acidification by the lactic acid bacteria. Some small curd particles will form.
  2. Slowly add about 10 ml of vinegar per litre of whey with gentle agitation. You will see more curd particles forming and the whey will become less 'milky'.
  3. Pour into a cloth to separate the curds. After the curd is dripped dry it is ready to eat. Use it in lasagna or eat as a side dish along with the main course or use it like cottage cheese in salads. 

Notes 

Before heating the whey, you can add up to 10% whole milk (that is, 100 ml of milk in 1 litre of whey). Addition of milk will help form larger curds which are easier to separate and the cheese will have a better texture. You also have to add more vinegar depending on the amount of milk. Continue adding vinegar until the whey is quite clear. By adding the vinegar slowly over a time period of about 5 minutes you will obtain better quality curd and it will be easier to know when to stop.

Cheese - the long version

Please jump to the top page of our extensive Cheese Making Technology section.

Yogurt and Fermented Beverages

Yogurt (also spelled yogourt or yoghurt) is a semi-solid fermented milk product that originated centuries ago and has evolved from many traditional Eastern European (e.g., Turkish and Bulgarian) products. The word is from the Turkish Yogen, meaning thick. It's popularity has grown and is now consumed in most parts of the world. Although the consistency, flavour and aroma may vary from one region to another, the basic ingredients and manufacturing are essentially consistent:

Ingredients

Although milk of various animals has been used for yogurt production in various parts of the world, most of the industrialized yogurt production uses cow's milk. Whole milk, partially skimmed milk, skim milk or whole milk enriched with cream may be used, to lower or raise the fat content as desired. In order to ensure the development of the yogurt culture the following criteria for the raw milk must be met:

  • low bacteria count
  • free from antibiotics, sanitizing chemicals, mastitis milk, colostrum, and rancid milk
  • no contamination by bacteriophages

Other yogurt ingredients may include some or all of the following:
Other Dairy Products: concentrated skim milk, nonfat dry milk, whey, lactose. These products are often used to increase the nonfat solids content. Reconstitution of these milk solids ingredients with water can also be used to standardize the solids-not-fat content, if permitted based on regulations of the legal jurisdiction.
Sweeteners: glucose or sucrose, high-intensity sweeteners (e.g. aspartame)
Stabilizers: gelatin, carboxymethyl cellulose, locust bean gum, guar, alginates, carrageenans, whey protein concentrate
Flavours
Fruit Preparations
: including natural and artificial flavouring, colour

Starter culture

The starter culture for most yogurt production in North America is a symbiotic blend of Streptococcus thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB). Although they can grow independently, the rate of acid production is much higher when used together than either of the two organisms grown individually. ST grows faster and produces both acid and carbon dioxide. The formate and carbon dioxide produced stimulates LB growth. On the other hand, the proteolytic activity of LB produces stimulatory peptides and amino acids for use by ST. These microorganisms are ultimately responsible for the formation of typical yogurt flavour and texture. The yogurt mixture coagulates during fermentation due to the drop in pH. The streptococci are responsible for the initial pH drop of the yogurt mix to approximately 5.0. The lactobacilli are responsible for a further decrease to pH 4.5. The following fermentation products contribute to flavour:

  • lactic acid
  • acetaldehyde
  • acetic acid
  • diacetyl

Manufacturing Method

The milk is clarified and separated into cream and skim milk, then standardized with other dairy ingredients to achieve the desired fat and milk solids-not-fat content. The various ingredients are then blended together in a mix tank equipped with a powder funnel and an agitation system. The mixture is then pasteurized using a continuous plate heat exchanger for 30 min at 85° C or 10 min at 95° C. These heat treatments, which are much more severe than fluid milk pasteurization, are necessary to achieve the following:

  • produce a relatively sterile and conducive environment for the starter culture
  • denature and coagulate whey proteins to enhance the viscosity and texture; this effect results from modification of the surface of the casein micelle so that milk thickens in a structurally-different manner than it would in a non-heated acid gel

The mix is then homogenized using high pressures of 2000-2500 psi. Besides thoroughly mixing the stabilizers and other ingredients, homogenization also prevents creaming and wheying off during incubation and storage. Stability, consistency and body are enhanced by homogenization. Once the homogenized mix has cooled to an optimum growth temperature, the yogurt starter culture is added.

A ratio of 1:1, ST to LB, inoculation is added to the jacketed fermentation tank. A temperature of 43° C is maintained for 2-2.5 h under quiescent (no agitation) conditions. This temperature is a compromise between the optimums for the two microorganisms (ST 39° C; LB 45° C). The titratable acidity is carefully monitored until the TA is 0.85 to 0.90% (pH 4.5). At this time the jacket is replaced with cool water and agitation begins, both of which stop the fermentation. The coagulated product is cooled to 5-22° C, depending on the product. Fruit and flavour may be incorporated at this time, then packaged. The product is now cooled and stored at refrigeration temperatures (5° C) to slow down the physical, chemical and microbiological degradation.

Yogurt Products

There are two types of plain yogurt:

  • Stirred style yogurt
  • Set style yogurt - The above description is essentially the manufacturing procedures for stirred style. In set style, the yogurt is packaged immediately after inoculation with the starter and is incubated in the packages.

Other yogurt products include:

  • Sweetened stirred style yogurt with fruit preparation
  • Fruit-on-the-bottom set style: - fruit mixture is layered at the bottom followed by inoculated yogurt, incubation occurs in the sealed cups
  • Soft-serve and Hard Pack frozen yogurt (see Frozen desserts section)
  • Probiotic yogourts: it has become quite common to add probiotic bacterial strains to yogourt (those with proven health-promoting benefits, in addition to ST and LB. These could include Lactobacillus acidophilus, Lactobacilus casei, or Bifidobacterium spp. When probiotics are added, it has also become common to add ingredients known as prebiotics, such as inulin, which will, after digestion, aid in the growth of the probiotics in the colon. Inulin, for example, is a polymer of fructose (fructo-oligosaccharide) that is indigestible in the small intestine because we do not have sufficient enzymes to cleave the fructose bonds. However, in the colon, bacterial enzymes can easily release free fructose, which has been shown to positively affect the growth of the probiotic organisms. 

Yogurt Beverages

Drinking yogurt is essentially stirred yogurt that has a sufficiently low total solids content to achieve a liquid or pourable consistency and which has undergone homogenization to further reduce the viscosity. Fat and solids-not-fat can both be standardized. If the desired snf level in the product is lower than it is in whole milk or skimmed milk, then dilution with water of fruit juices may be used, depending on the requirements of the legal jurisdiction. Sweeteners, flavouring and colouring are invariably added. Heat treatment may be applied to extend the storage life, although this would reduce or eliminate the viable yogourt culture organisms. HTST pasteurization with aseptic processing will give a shelf life of several weeks at 2-4°C, while UHT processes with aseptic packaging will give a shelf life of several weeks at room temperature.

Other Fermented Milk Beverages

Cultured Buttermilk

This product was originally the fermented byproduct of butter manufacture, but today it is more common to produce cultured buttermilks from skim or whole milk. The culture most frequently used in Loctococcus lactis, perhaps also subsp. cremoris or diacetylactis. Milk is usually heated to 95°C and cooled to 20-25°C before the addition of the starter culture. Starter is added at 1-2% and the fermentation is allowed to proceed for 16-20 hours, to an acidity of 0.9% lactic acid. This product is frequently used as an ingredient in the baking industry, in addition to being packaged for sale in the retail trade.

Acidophilus milk

Acidophilus milk is a traditional milk fermented with Lactobacillus acidophilus (LA), which has been thought to have therapeutic benefits in the gastrointestinal tract. Skim or whole milk may be used. The milk is heated to high temperature, e.g., 95°C for 1 hour, to reduce the microbial load and favour the slow growing LA culture. Milk is inoculated at a level of 2-5% and incubated at 37°C until coagulated. Some acidophilus milk has an acidity as high as 1% lactic acid, but for therapeutic purposes 0.6-0.7% is more common.

Another variation has been the introduction of a sweet acidophilus milk, one in which the LA culture has been added but there has been no incubation. It is thought that the culture will reach the GI tract where its therapeutic effects will be realized, but the milk has no fermented qualities, thus delivering the benefits without the high acidity and flavour, considered undesirable by some people. 

Sour Cream

Cultured cream usually has a fat content between 12-30%, depending on the required properties. The starter is similar to that used for cultured buttermilk. The cream after standardization is usually heated to 75-80°C and is homogenized at >13 MPa to improve the texture. Inoculation and fermentation conditions are also similar to those for cultured buttermilk, but the fermentation is stopped at an acidity of 0.6%. 

Others

There are a great many other fermented dairy products, including kefir, koumiss, beverages based on bulgaricus or bifidus strains, labneh, and a host of others. Many of these have developed in regional areas and, depending on the starter organisms used, have various flavours, textures, and components from the fermentation process, such as gas or ethanol.

Butter Manufacture

Butter is essentially the fat of the milk. It is usually made from sweet cream and is salted. However, it can also be made from acidulated or bacteriologically soured cream and saltless (sweet) butters are also available. Well into the 19th century butter was still made from cream that had been allowed to stand and sour naturally. The cream was then skimmed from the top of the milk and poured into a wooden tub. Buttermaking was done by hand in butter churns. The natural souring process is, however, a very sensitive one and infection by foreign micro-organisms often spoiled the result. Today's commercial buttermaking is a product of the knowledge and experience gained over the years in such matters as hygiene, bacterial acidifying and heat treatment, as well as the rapid technical development that has led to the advanced machinery now used. The commercial cream separator was introduced at the end of the 19th century, the continuous churn had been commercialized by the middle of the 20th century.

Definitions and Standards

Milkfat

the lipid components of milk, as produced by the cow, and found in commercial milk and milk-derived products, mostly comprised of triglyceride.

Butterfat

almost synonymous with milkfat; all of the fat components in milk that are separable by churning.

Anhydrous Milkfat (AMF) 

the commercially- prepared extraction of cow's milkfat, found in bulk or concentrated form (comprised of 100% fat, but not necessarily all of the lipid components of milk).

Butteroil 

synonymous with anhydrous milkfat; (conventional terminology in the fats and oils field differentiates an oil from a fat based on whether it is liquid at room temp. or solid, but very arbitrary).

Butter 

a water-in-oil emulsion, comprised of >80% milkfat, but also containing water in the form of tiny droplets, perhaps some milk solids-not-fat, with or without salt (sweet butter); texture is a result of working/kneading during processing at appropriate temperatures, to establish fat crystalline network that results in desired smoothness (compare butter with melted and recrystallized butter); used as a spread, a cooking fat, or a baking ingredient.

The principal constituents of a normal salted butter are fat (80 - 82%), water (15.6 - 17.6%), salt (about 1.2%) as well as protein, calcium and phosphorous (about 1.2%). Butter also contains fat-soluble vitamins A, D and E.

Butter should have a uniform colour, be dense and taste clean. The water content should be dispersed in fine droplets so that the butter looks dry. The consistency should be smooth so that the butter is easy to spread and melts readily on the tongue.

Overview of the Buttermaking Process

Buttermaking Process Flowchart

The buttermaking process involves quite a number of stages. The continuous buttermaker has become the most common type of equipment used.

The cream can be either supplied by a fluid milk dairy or separated from whole milk by the butter manufacturer. The cream should be sweet (pH >6.6, TA = 0.10 - 0.12%), not rancid and not oxidized.

If the cream is separated by the butter manufacturer, the whole milk is preheated to the required temperature in a milk pasteurizer before being passed through a separator. The cream is cooled and led to a storage tank where the fat content is analyzed and adjusted to the desired value, if necessary. The skim milk from the separator is pasteurized and cooled before being pumped to storage. It is usually destined for concentration and drying.

From the intermediate storage tanks, the cream goes to pasteurization at a temperature of 95oC or more. The high temperature is needed to destroy enzymes and micro-organisms that would impair the keeping quality of the butter.

If ripening is desired for the production of cultured butter, mixed cultures of S. cremoris, S. lactis diacetyl lactis, Leuconostocs, are used and the cream is ripened to pH 5.5 at 21oC and then pH 4.6 at 13oC. Most flavour development occurs between pH 5.5 - 4.6. The colder the temperature during ripening the more the flavour development relative to acid production. Ripened butter is usually not washed or salted.

In the aging tank, the cream is subjected to a program of controlled cooling designed to give the fat the required crystalline structure. The program is chosen to accord with factors such as the composition of the butterfat, expressed, for example, in terms of the iodine value which is a measure of the unsaturated fat content. The treatment can even be modified to obtain butter with good consistency despite a low iodine value, i.e. when the unsaturated proportion of the fat is low.

As a rule, aging takes 12 - 15 hours. From the aging tank, the cream is pumped to the churn or continuous buttermaker via a plate heat exchanger which brings it to the requisite temperature. In the churning process the cream is violently agitated to break down the fat globules, causing the fat to coagulate into butter grains, while the fat content of the remaining liquid, the buttermilk, decreases.

Thus the cream is split into two fractions: butter grains and buttermilk. In traditional churning, the machine stops when the grains have reached a certain size, whereupon the buttermilk is drained off. With the continuous buttermaker the draining of the buttermilk is also continuous.

After draining, the butter is worked to a continuous fat phase containing a finely dispersed water phase. It used to be common practice to wash the butter after churning to remove any residual buttermilk and milk solids but this is rarely done today.

Salt is used to improve the flavour and the shelf-life, as it acts as a preservative. If the butter is to be salted, salt (1-3%) is spread over its surface, in the case of batch production. In the continuous buttermaker, a salt slurry is added to the butter. The salt is all dissolved in the aqueous phase, so the effective salt concentration is approximately 10% in the water.

After salting, the butter must be worked vigorously to ensure even distribution of the salt. The working of the butter also influences the characteristics by which the product is judged - aroma, taste, keeping quality, appearance and colour. Working is required to obtain a homogenous blend of butter granules, water and salt. During working, fat moves from globular to free fat. Water droplets decrease in size during working and should not be visible in properly worked butter. Overworked butter will be too brittle or greasy depending on whether the fat is hard or soft. Some water may be added to standardize the moisture content. Precise control of composition is essential for maximum yield.

The finished butter is discharged into the packaging unit, and from there to cold storage.

The background science of butter churning

The fat globule

Milk fat is comprised mostly of triglycerides, with small amounts of mono- and diglycerides, phospholipids, glycolipids, and lipo-proteins. The trigylcerides (98% of milkfat) are of diverse composition with respect to their component fatty acids, approximately 40% of which are unsaturated fat firmness varies with chain length, degree of unsaturation, and position of the fatty acids on the glycerol. Fat globules vary from 0.1 - 10 micron in diameter. The fat globule membrane is comprised of surface active materials: phospholipids and lipoproteins.

Fat globules typically aggregate in three ways:

  • flocculation
  • coalescence
  • partial coalescence

Whipping and Churning

Many milk products foam easily. Skim milk foams copiously with the amount of foam being very dependent on the amount of residual fat - fat depresses foaming. The foaming agents are proteins, the amount of proteins in the foam are proportional to their contents in milk. Foaming is decreased in heat treated milk, possibly because denaturated whey proteins produce a more brittle protein layer at the interface. Fats tend to spread over the air-water interface and destabilize the foam; very small amounts of fats (including phospholipids) can destabilize a foam.

During the interaction of fat globules with air bubbles the globule may also be disrupted (this is the only way that fat globules can be disrupted without considerable energy input). Disruption of the fat globule by interaction between the fat globule and air bubbles is rare except in the case of newly formed air bubbles where the air-water interfacial layer is still thin. If part of the fat globule is solid, churning will result, hence the term "flotation churning" -from repeated rupturing of air bubbles and resulting coalescence of the adsorbed fat.

In spite of the above comments on the destabilization of foams by fat, milk fat is essential for the formation of stable whipped products which depend on the interaction between fat globules, air bubbles and plasma components (esp. proteins).

When cream is beaten air cells form more slowly partly because of higher viscosity and partly because the presence of fat causes immediate collapse of most of the larger bubbles. If most of the fat is liquid (high temperature) the fat globule membrane is not readily punctured and churning does not occur -at cold temperature where solid fat is present, churning (clumping) of the fat globule takes place. Clumps of globules begin to associate with air bubbles so that a network of air bubbles and fat clumps and globules form entrapping all the liquid and producing a stable foam. If beating continues the fat clumps increase in size until they become too large and too few to enclose the air cells, hence air bubbles coalesce, the foam begins to "leak" and ultimately butter and butter milk remain.

Crystallizing of the milkfat during aging

Before churning, cream is subjected to a program of cooling designed to control the crystallization of the fat so that the resultant butter has the right consistency. The consistency of butter is one of its most important quality-related characteristics, both directly and indirectly, since it affects the other characteristics - chiefly taste and aroma. Consistency is a complicated concept and involves properties such as hardness, viscosity, plasticity and spreading ability.

The relative amounts of fatty acids with high melting point determine whether the fat will be hard or soft. Soft fat has a high content of low-melting fatty acids and at room temperature this fat has a large continuous fat phase with a low solid phase, i.e. crystallized, high-melting fat. On the other hand, in a hard fat, the solid phase of high-melting fat is much larger than the continuous fat phase of low-melting fatty acids.

In buttermaking, if the cream is always subjected to the same heat treatment it will be the chemical composition of the milk fat that determines the butter's consistency. A soft milk fat will make a soft and greasy butter, whereas butter from hard milk fat will be hard and stiff. If, however, the heat treatment is modified to suit the iodine value of the fat, the consistency of the butter can be optimized. For the heat treatment regulates the size of the fat crystals, and the relative amounts of solid fat and the continuous phase - the factors that determine the consistency of the butter.

Pasteurization causes the fat in the fat globules to liquefy. And when the cream is subsequently cooled a proportion of the fat will crystallize. If cooling is rapid, the crystals will be many and small; if gradual the yield will be fewer but larger crystals. The more violent the cooling process, the more will be the fat that will crystallize to form the solid phase, and the less the liquid fat that can be squeezed out of the fat globules during churning and working.

The crystals bind the liquid fat to their surface by adsorption. Since the total surface area is much greater if the crystals are many and small, more liquid fat will be adsorbed than if the crystals were larger and fewer. In the former case, churning and working will press only a small proportion of the liquid fat from the fat globules. The continuous fat phase will consequently be small and the butter firm. In the latter case, the opposite applies. A larger amount of liquid fat will be pressed out; the continuous phase will be large and the butter soft.

So by modifying the cooling program for the cream, it is possible to regulate the size of the crystals in the fat globules and in this way influence both the magnitude and the nature of the important continuous fat phase.

 

Tempering Treatment of Hard Fat. For optimum consistency where the iodine value is low, i.e. the butterfat is hard, as much as possible of the hardest fat must be converted to as few crystals as possible, so that little of the liquid fat is bound to the crystals. The liquid fat phase in the fat globules will thereby be maximized and much of it can be pressed out during churning and working, resulting in butter with a relatively large continuous phase of liquid fat and with the hard fat concentrated to the solid phase.

The program of treatment necessary to achieve this result comprises the following stages:

  • rapid cooling to about 8oC and storage for about 2 hours at this temperature;
  • heating gently to 20 - 21oC and storage at this temperature for at least 2 hours (water at 27 - 29oC is used for heating);
  • cooling to about 16oC.

Cooling to about 8oC causes the formation of a large number of small crystals that bind fat from the liquid continuous phase to their surface.

When the cream is gently heated to 20 - 21oC the bulk of the crystals melt, leaving only the hard fat crystals which, during the storage period at 20 - 21oC, grow larger.

After 1 - 2 hours most of the hard fat has crystallized, binding little of the liquid fat. By dropping the temperature now to about 16oC, the hardest portion of the fat will be fixed in crystal form while the rest is liquefied. During the holding period at 16oC, fat with a melting point of 16oC or higher will be added to the crystals. The treatment has thus caused the high-melting fat to collect in large crystals with little adsorption of the low-melting liquid fat, so that a large proportion of the butter oil can be pressed out during churning and working.

 

Tempering Treatment of Medium Hard Fat. With an increase in the iodine value, the heating temperature is accordingly reduced from 20-21oC. Consequently a larger number of fat crystals will form and more liquid fat will be adsorbed than is the case with the hard fat program. For iodine values up to 39, the heating temperature can be as low as 15oC.

 

Tempering Treatment of Very Soft Fat. Where the iodine value is greater than 39-40 the "summer method" of treatment is used. After pasteurization the cream is cooled to 20oC. If the iodine value is around 39 - 40 the cream is cooled to about 8oC, and if 41 or greater to 6oC. It is generally held that aging temperatures below the 20o level will give a soft butter..

 

 

 

Butter structure

Diagram of Butter Structure

It should now be obvious from the discussions regarding the background science of churning and the crystallization processes that the structure of butter is quite complicated. The size and extent of crystal networks both within the globules and within the non-globular phases is controlled to a large extent by milkfat's variable composition and by the aging process. The extent of globular versus non-globular fat is controlled to a large extent also by the amount of physical working applied to the butter post-churning.
 

Continuous Buttermaking

There are essentially four types of buttermaking processes:

  • traditional batch churning from 25- 35% mf. cream;
  • continuous flotation churning from 30-50% mf. cream;
  • the concentration process whereby "plastic" cream at 82% mf. is separated from 35% mf. cream at 55oC and then this oil-in-water emulsion cream is inverted to a water-in-oil emulsion butter with no further draining of buttermilk;
  • the anhydrous milkfat process whereby water, SNF, and salt are emulsified into butter oil in a process very similar to margarine manufacture.

An optimum churning temperature must be determined for each type of process but is mainly dependent on the mean melting point and melting range of the lipids, as discussed above, i.e., 7-10oC in summer and 10 - 13oC in winter. If churning temperature is too warm or if the thermal cream aging cycle permits too much liquid fat, then a soft greasy texture results; if too cold or too much solid fat, then butter becomes too brittle.

Continuous Flotation Churns

Continuous butter churn diagram

The cream is first fed into a churning cylinder fitted with beaters that are driven by a variable speed motor.

Rapid conversion takes place in the cylinder and, when finished, the butter grains and buttermilk pass on to a draining section. The first washing of the butter grains sometimes takes place en route - either with water or recirculated chilled buttermilk. The working of the butter commences in the draining section by means of a screw, which also conveys it to the next stage.

On leaving the working section the butter passes through a conical channel to remove any remaining buttermilk. Immediately afterwards, the butter may be given its second washing, this time by two rows of adjustable high-pressure nozzles. The water pressure is so high that the ribbon of butter is broken down into grains and consequently any residual milk solids are effectively removed. Following this stage, salt may be added through a high-pressure injector.

The third section in the working cylinder is connected to a vacuum pump. Here it is possible to reduce the air content of the butter to the same level as conventionally churned butter.

In the final or mixing section the butter passes a series of perforated disks and star wheels. There is also an injector for final adjustment of the water content. Once regulated, the water content of the butter deviates less than +/- 0.1%, provided the characteristics of the cream remain the same.

The finished butter is discharged in a continuous ribbon from the end nozzle of the machine and then into the packaging unit.

Concentration Method

  • 30% fat cream pasteurized at 90oC
  • degassed in a vacuum
  • cooled to 45-70oC
  • separated to 82% fat ("plastic" cream)
  • the concentrate, still an O/W emulsion, is cooled to 8-13oC
  • fat crystals forming in the tightly packed globules perforate the membranes, cause liquid fat leakage and rapid phase inversion
  • contrast to mayonnaise, also a o/w emulsion at 82% fat but is winterized to prevent crystallization
  • butter from this method contains all membrane material, therefore, more phospholipids
  • no butter milk produced
  • after phase inversion the butter is worked and salted.

Phase Separation

 Butter from anhydrous milkfat:

  • prepare "plastic" cream (>80% fat)
  • heat with agitation to destabilize emulsion
  • separate oil from aqueous phase: 82 to 98% butter fat
  • this butter oil is then blended with water, salt and milk solids in an emulsion pump and transferred to a scraped surface heat exchanger for cooling and to initiate crystallization
  • further worked to develop crystal structure and texture
  • process similar to margarine manufacture
  • margarine has advantage of fat composition control to modify physical properties
  • butter produced by phase separation contains few phospholipids.

Butter Yield Calculations

Technological limits to yield efficiency are defined by separation efficiency, churning efficiency, composition overrun, and package over fill.

Separation efficiency (Es)

 - represents fat transferred from milk to cream 

Es = 1 - fs/fm 
where fs = skim fat as percent w/w
 fm = milk fat as percent w/w

Separation efficiency depends on initial milk fat content and residual fat in the skim. Assuming optimum operation of the separator, the principal determining factor of fat loss to the skim is fat globule size. Modern separators should achieve a skim fat content of 0.04 - 0.07%.

Churning Efficiency (Ec)

 - represents fat transferred from cream to butter

Ec = 1 - fbm/fc 
where fbm = buttermilk fat as percent w/w
fc = cream fat as percent w/w

Maximum acceptable fat loss in buttermilk is about 0.7% of churned fat corresponding to a churning efficiency of 99.3% of cream fat recovered in the butter. Churning efficiency is highest in the winter months and lowest in the summer months. Fat losses are higher in ripened butter due to a restructuring of the FGM (possibly involving crystallization of high melting triglycerides on the surface of the globules). If churning temperature is too high, churning occurs more quickly but fat loss in buttermilk increases. For continuous churns assuming 45% cream, churning efficiency should be 99.61 - 99.42%.

Composition Overrun

% Churn Overrun 

= (Kg butter made - Kg fat churned)/Kg fat churned x 100 %

% Composition Overrun 
= (100 - % fat in butter)/% fat x 100 %

Package Fill Control

 = (actual wt. - nominal wt.)/nominal wt. x 100%

An acceptable range for 25 kg butter blocks is 0.2 - 0.4% overfill. Overfill on 454 g prints is about 0.6%.

Other factors affecting yield

  • shrinkage due to leaky butter (improperly worked).
  • shrinkage due to moisture loss; avoided by aluminum wrap.
  • loss of butter remnants on processing equipment; % loss minimal in large scale continuous processing.

Plant Overrun

Plant efficiency or plant overrun is the sum of separation, churning, composition overrun and package fill efficiencies. In summary the theoretical maximum efficiency values are:

Separation Efficiency 98.85 
Churning Efficiency 99.60 
Composition overrun (% fat) 23.30 
Package overfill 0.20

These values can be used to predict the expected yield of butter per kg of milk or kg of milk fat received.

Example

3.6% m.f. milk

0.05% m.f. in skim
40% m.f. in cream
0.3% m.f. in buttermilk
81.5% m.f. in butter

Es = 1 - .05/3.6 = 98.6
Ec = 1 - .3/40 = 99.25
% Composition Overrun = (100-81.5)/81.5 = 22.7%
If 100 kg of milk was used, 8.9 kg of cream would be produced (from a Pearson Square mass balance) and 4.35 kg butter would be produced from that. This is the theoretical yield based on no losses. The mass balance of fat shows that 98.3% of the fat ended up in the butter, 0.4% of the fat ended up in the buttermilk and 1.3% of the fat ended up in the skim.
The % Churn Overrun = (4.35 - 3.6)/3.6 = 20.8%

Whipped Butter

Whipped butter is typically used in foodservice situations. The main advantage of whipped butter is increased spreadability even at refrigeration temperatures, thus providing great advantage for the restaurant industry. The volume increase is usually 25 - 30%. Whipping is achieved by injecting an inert gas (nitrogen) into the butter after churning. In the phase separation process, whipping can be achieved by injecting nitrogen in the crystallizer as is done in the production of whipped margarine.

Anhydrous Milkfat ("butter oil")

Anhydrous milk fat, butter oil, can be manufactured from either butter or from cream. For the manufacture from butter, non-salted butter from sweet cream is normally used, and the process works better if the butter is at least a few weeks old. Melted butter is passed through a centrifuge, to concentrate the fat to 99.5% of greater. This oil is heated again to 90-95oC and vacuum cooled before packaging.

The processes for the production of anhydrous fat, using cream as the raw material, are based on the emulsion splitting principle. In brief, the processes consist of the cream first being concentrated to 75% fat or greater, in two stages. In both of these stages, the fat is concentrated in a hermetic solids-ejecting separator. The fat globules are then broken down mechanically, so that phase inversion occurs and the fat is liberated. This forms a continuous fat phase containing dispersed water droplets, which can be separated from the fat phase by centrifugation. This is similar to the concentration method for buttermaking, with the addition of the mechanical rupture of the emulsion and additional separator for removal of the residual water phase.

One of the key machines in the system is the mechanical device for phase inversion. This can be in the form of a centrifugal separator equipped with a serrated disc. The disc breaks down the emulsion, so that the liquid leaving the machine is a continuous oil phase, with dispersed water droplets and buttermilk. Larger equipment could be equipped with a motor-driven serrated disc or with a homogenizer. After phase inversion, the fat is concentrated to 99.5% or greater in a hermetic separator.

Fractionation of anhydrous milk fat

Milk fat is a complicated mixture of triglycerides that contain numerous fatty acids of varying carbon chain lengths and degrees of saturation. The proportions of the various fatty acids present will also vary depending on the conditions surrounding the production of milk.

One method of milkfat fraction is by thermal treatment. The mixture can be separated into fractions on the basis of their melting point. The technique consists of melting the entire quantity of fat and then cooling it down to a predetermined temperature. The triglycerides with the higher melting point will then crystallize and settle out.

In the modern thermal fractionation method, sedimentation by gravity is replaced by centrifugal separation. Since a modern separator generates a force that is thousands of times greater than the force of gravity and since the sedimentation distances are very short, the process is incomparably faster. The crystallizing stage can also be accelerated, since the crystals need not be large if centrifugal separation is employed.

Fractionation of milkfat can also be accomplished by supercritical fluid extraction techniques.
Some of this material has been condensed from the Alfa-Laval Dairy Handbook, with permission.

Ice Cream

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Milk Ingredients

Various milk ingredients, including concentrated and dried milk powdersmilk and whey protein concentratescheesesmilkfat ingredients, etc., are used in many food applications, including bakery, meats, sauces, fabricated foods, etc.

For a website devoted to discussion of milk ingredients, including Canadian suppliers, please go to: 

www.milkingredients.ca