Soured milk

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Soured milk
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Russian and Ukrainian prostokvasha, traditional fermented milk
Main ingredients Milk

Soured milk denotes a range of food products produced by the acidification of milk. Acidification, which gives the milk a tart taste, is achieved either through bacterial fermentation or through the addition of an acid, such as lemon juice or vinegar. The acid causes milk to coagulate and thicken, inhibiting the growth of harmful bacteria and improving the product's shelf life.


Soured milk that is produced by bacterial fermentation is more specifically called fermented milk or cultured milk . [1] Traditionally, soured milk was simply fresh milk that was left to ferment and sour by keeping it in a warm place for a day, often near a stove. Modern commercial soured milk may differ from milk that has become sour naturally. [2] [ full citation needed ]

Soured milk that is produced by the addition of an acid, with or without the addition of microbial organisms, is more specifically called acidified milk. [1] In the United States, acids used to manufacture acidified milk include acetic acid (commonly found in vinegar), adipic acid, citric acid (commonly found in lemon juice), fumaric acid, glucono-delta-lactone, hydrochloric acid, lactic acid, malic acid, phosphoric acid, succinic acid, and tartaric acid.

Soured milk is commonly made at home or is sold and consumed in Europe, especially in Eastern Europe (Bulgaria, Belarus, Poland, Slovakia, Russia, Ukraine), all over the countries of the former Yugoslavia (Macedonia, Serbia, Montenegro, Bosnia and Herzegovina, Croatia, Slovenia), Romania, Hungary, Greece, Finland, Germany, and Scandinavia.

It is also made at home or sold in supermarkets and consumed in the Great Lakes region of Somalia and Eastern Africa (Kenya, Uganda, Rwanda, Burundi and Tanzania). It is also a traditional food of the Bantu people of Southern Africa.

Since the 1970s, some producers have used chemical acidification in place of biological agents. [3] [4] [5] [6]

In recipes

Raw milk that has not gone sour is sometimes referred to as "sweet milk", because it contains the sugar lactose. Fermentation converts the lactose to lactic acid, which has a sour flavor. Before the invention of refrigeration, raw milk commonly became sour before it could be consumed, and various recipes incorporate such leftover milk as an ingredient. Sour milk produced by fermentation differs in flavor from that produced by acidification, because the acids commonly added in commercial manufacture have different flavors from lactic acid, and also because fermentation can introduce new flavors. Buttermilk is a common modern substitute for naturally soured milk.

See also

Related Research Articles

Dairy product Food produced from or containing the milk of mammals

Dairy products or milk products are a type of food produced from or containing the milk of mammals. They are primarily produced from mammals such as cattle, water buffaloes, goats, sheep, camels and humans. Dairy products include food items such as yogurt, cheese and butter. A facility that produces dairy products is known as a dairy, or dairy factory. Dairy products are consumed worldwide, with the exception of most of East and Southeast Asia and parts of central Africa.

Rennet Complex of enzymes from the stomachs of calves, used in the production of cheese

Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. Chymosin, its key component, is a protease enzyme that curdles the casein in milk. In addition to chymosin, rennet contains other enzymes, such as pepsin and a lipase.

Yogurt A food produced by bacterial fermentation of milk

Yogurt, also spelled yoghurt, yogourt or yoghourt, is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as yogurt cultures. The fermentation of lactose by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and characteristic tart flavor. Cow's milk is commonly available worldwide and, as such, is the milk most commonly used to make yogurt. Milk from water buffalo, goats, ewes, mares, camels, and yaks is also used to produce yogurt where available locally. The milk used may be homogenized or not. It may be pasteurized or raw. Each type of milk produces substantially different results.

Salami Cured sausage, fermented and air-dried meat

Salami is a cured sausage consisting of fermented and air-dried meat, typically pork. Historically, salami was popular among Southern, Eastern, and Central European peasants because it can be stored at room temperature for up to 40 days once cut, supplementing a potentially meager or inconsistent supply of fresh meat. Countries and regions across Europe make their own traditional varieties of salami.

Lactic acid fermentation

Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars are converted into cellular energy and the metabolite lactate, which is lactic acid in solution. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.

Curd Dairy product

Curd is a dairy product obtained by coagulating milk in a process called curdling. The coagulation can be caused by adding rennet or any edible acidic substance such as lemon juice or vinegar, and then allowing it to coagulate. The increased acidity causes the milk proteins (casein) to tangle into solid masses, or curds. Milk that has been left to sour will also naturally produce curds, and sour milk cheeses are produced this way. Producing cheese curds is one of the first steps in cheesemaking; the curds are pressed and drained to varying amounts for different styles of cheese and different secondary agents are introduced before the desired aging finishes the cheese. The remaining liquid, which contains only whey proteins, is the whey. In cow's milk, 90 percent of the proteins are caseins.

Buttermilk fermented dairy drink

Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream; however, most modern buttermilk is cultured. It is common in warm climates where unrefrigerated fresh milk sours quickly.

<i>Lactobacillus delbrueckii <span style="font-style:normal;">subsp.</span> bulgaricus</i> Subspecies of bacteria and the main bacteria used for the production of yogurt

Lactobacillus delbrueckii subsp. bulgaricus is one of over 200 published species in the Lactobacillus genome complex (LGC) and is the main bacterium used for the production of yogurt. It also plays a crucial role in the ripening of some cheeses, as well as in other processes involving naturally fermented products. It is defined as homofermentive lactic acid bacteria due to lactic acid being the single end product of its carbohydrate digestion. It is also considered a probiotic.


Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and winemaking is known as oenology. A winemaker may also be called a vintner. The growing of grapes is viticulture and there are many varieties of grapes.

Blue cheese

Blue cheese or bleu cheese is cheese made with cultures of the mold Penicillium, giving it spots or veins of the mold throughout the cheese, which can vary in color through various shades of blue and green. This carries a distinct smell, either from that or various specially cultivated bacteria. Some blue cheeses are injected with spores before the curds form, and others have spores mixed in with the curds after they form. Blue cheeses are typically aged in a temperature-controlled environment such as a cave. Blue cheese can be eaten by itself or can be spread, crumbled or melted into or over a range of other foods. Blue cheese is known for its pungent creamy texture.

Fermentation in food processing Converting carbohydrates to alcohol or acids using anaerobic microorganisms

Fermentation in food processing is the process of converting carbohydrates to alcohol or organic acids using microorganisms—yeasts or bacteria—under anaerobic conditions. Fermentation usually implies that the action of microorganisms is desired. The science of fermentation is known as zymology or zymurgy.

Leuconostoc mesenteroides is a species of lactic acid bacteria associated with fermentation, under conditions of salinity and low temperatures. In some cases of vegetable and food storage, it was associated with pathogenicity. L. mesenteroides is approximately 0.5-0.7 µm in diameter and has a length of 0.7-1.2 µm, producing small grayish colonies that are typically less than 1.0 mm in diameter. It is facultatively anaerobic, Gram-positive, non-motile, non-sporogenous, and spherical. It often forms lenticular coccoid cells in pairs and chains, however, it can occasionally forms short rods with rounded ends in long chains, as its shape can differ depending on what media the species is grown on. L. mesenteroides grows best at 30°C, but can survive in temperatures ranging from 10°C to 30°C. Its optimum pH is 5.5, but can still show growth in pH of 4.5-7.0.

Cheese Dairy product created by coagulating the milk protein casein

Cheese is a dairy product, derived from milk and produced in wide ranges of flavours, textures and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During production, the milk is usually acidified and adding the enzymes of rennet causes the milk proteins (casein) to coagulate. The solids (curd) are separated from the liquid (whey) and pressed into final form. Some cheeses have aromatic molds on the rind, the outer layer, or throughout. Most cheeses melt at cooking temperature.

Sodium lactate

Sodium lactate is the sodium salt of lactic acid, and has a mild saline taste. It is produced by fermentation of a sugar source, such as corn or beets, and then, by neutralizing the resulting lactic acid to create a compound having the formula NaC3H5O3.

Souring is a cooking technique that uses exposure to an acid to cause a physical and chemical change in food. This acid can be added explicitly, or can be produced within the food itself by a microbe such as Lactobacillus.

Kefir Fermented milk drink made from kefir grains

Kefir or kephir, is a fermented milk drink similar to a thin yogurt that is made from kefir grains, a specific type of mesophilic symbiotic culture. The drink originated in the North Caucasus, Eastern Europe and Russia, where it is prepared by inoculating cow, goat, or sheep milk with kefir grains.

Ymer (dairy product) Danish soured milk product (1930- )

Ymer is a Danish soured milk product which has been known since 1930. It is made by fermenting whole milk with the bacterial culture Lactococcus lactis. When producing fermented milk products such as yogurt, ymer, filmjölk, skyr, qvark and A-38, and also when producing cheese, one can add lactic acid bacteria which convert milk sugar in the milk into lactic acid and other substances. Acidity makes the milk thicker, gives it a tart flavor, and increases the shelf life by several days.


Naem is a pork sausage in Thai cuisine. It is a fermented food that has a sour flavor. It has a short shelf life, and is often eaten in raw form after the fermentation process has occurred. It is a popular Southeast Asian food, and different regions of Southeast Asia have various preferred flavors, including variations of sour and spicy. Naem is used as an ingredient in various dishes and is also served as a side dish.

Sour cream

Sour cream or soured cream is a dairy product obtained by fermenting regular cream with certain kinds of lactic acid bacteria. The bacterial culture, which is introduced either deliberately or naturally, sours and thickens the cream. Its name comes from the production of lactic acid by bacterial fermentation, which is called souring. Crème fraîche is one type of sour cream with a high fat content and less sour taste.

Industrial microbiology is a branch of biotechnology that applies microbial sciences to create industrial products in mass quantities, often using microbial cell factories. There are multiple ways to manipulate a microorganism in order to increase maximum product yields. Introduction of mutations into an organism may be accomplished by introducing them to mutagens. Another way to increase production is by gene amplification, this is done by the use of plasmids, and vectors. The plasmids and/ or vectors are used to incorporate multiple copies of a specific gene that would allow more enzymes to be produced that eventually cause more product yield. The manipulation of organisms in order to yield a specific product has many applications to the real world like the production of some antibiotics, vitamins, enzymes, amino acids, solvents, alcohol and daily products. Microorganisms play a big role in the industry, with multiple ways to be used. Medicinally, microbes can be used for creating antibiotics in order to treat antibiotics. Microbes can also be used for the food industry as well. Microbes are very useful in creating some of the mass produced products that are consumed by people. The chemical industry also uses microorganisms in order to synthesize amino acids and organic solvents. Microbes can also be used in an agricultural application for use as a biopesticide instead of using dangerous chemicals and or inoculants to help plant proliferation.


  1. 1 2 "TITLE 21--FOOD AND DRUGS: CHAPTER I, PART 131 MILK AND CREAM". Electronic Code of Federal Regulations (e-CFR). 2007-04-01. Retrieved 2007-11-18.
  2. "Dairy-Milk" . Retrieved 2014-03-01.
  3. Nakamura, Yasunori; Yamamoto, Naoyuki; Sakai, Kumi; Takano, Toshiaki (June 1, 1995). "Antihypertensive Effect of Sour Milk and Peptides Isolated from It That are Inhibitors to Angiotensin I-Converting Enzyme". Journal of Dairy Science . 78 (6): 1253–7. doi: 10.3168/jds.S0022-0302(95)76745-5 . PMID   7673515 . Retrieved 2007-06-30.
  4. Sukhov, SV; Kalamkarova, LI; Il'chenko, LA; Zhangabylov, AK (1986). "Microfloral changes in the small and large intestines of chronic enteritis patients on diet therapy including sour milk products". Voprosy pitaniia (in Russian). Jul-Aug (4): 14–7. PMID   3765530.
  5. USpatent 3625702,Exler, Heinrich,"PREPARATION OF SOUR MILK DRINKS",published 1971-12-07,issued 1971-12-07, assigned to Heinrich Exler
  6. USpatent 3978243,Pedersen, Jens Kristian,"Process for preparing gelled sour milk",published 1976-08-31,issued 1976-08-31, assigned to Kobenhavns Pektinfabrik