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.