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Kefir ( ; also spelled as kephir or kefier; ; ; ) is a fermented milk drink similar to a thin
yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial Fermentation (food), fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in t ...
or ayran that is made from kefir grains, a specific type of
mesophilic A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Organi ...
symbiotic culture. The drink originated in the
North Caucasus The North Caucasus, ( ady, Темыр Къафкъас, Temır Qafqas; kbd, Ишхъэрэ Къаукъаз, İṩxhərə Qauqaz; ce, Къилбаседа Кавказ, Q̇ilbaseda Kavkaz; , os, Цӕгат Кавказ, Cægat Kavkaz, inh, ...
, in particular the
Elbrus Mount Elbrus ( rus, links=no, Эльбрус, r=Elbrus, p=ɪlʲˈbrus; kbd, Ӏуащхьэмахуэ, 'uaşhəmaxuə; krc, Минги тау, Mingi Taw) is the highest and most prominent peak in Russia and Europe. It is situated in the we ...
region along the upper mountainous sections of Circassia, Karachay and
Balkaria The Balkars ( krc, Малкъарлыла, Malqarlıla or Таулула, , 'Mountaineers') are a Turkic people of the Caucasus region, one of the titular populations of Kabardino-Balkaria. Their Karachay-Balkar language is of the Ponto-Casp ...
, from where it came to Russia, and from there it spread to Europe and the United States, where it is prepared by inoculating the milk of cows, goats, or
sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated s ...
with kefir grains. Kefir is a breakfast, lunch, and dinner drink popular across
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
,
Belarus Belarus,, , ; alternatively and formerly known as Byelorussia (from Russian ). officially the Republic of Belarus,; rus, Республика Беларусь, Respublika Belarus. is a landlocked country in Eastern Europe. It is bordered by R ...
,
Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...
,
Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia a ...
,
Latvia Latvia ( or ; lv, Latvija ; ltg, Latveja; liv, Leţmō), officially the Republic of Latvia ( lv, Latvijas Republika, links=no, ltg, Latvejas Republika, links=no, liv, Leţmō Vabāmō, links=no), is a country in the Baltic region of ...
,
Lithuania Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...
,
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...
,
Romania Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
, and
Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...
- where it is known as an affordable health drink. It is also known in
Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
,
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
, and
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
, where
buttermilk Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream. As most modern butter in western countries is not made with cultured cream but uncultured sweet cream, most mod ...
-type fermented dairy drinks are common. Kefir is common particularly among Russian and Estonian minorities. In South Slavic countries, kefir is consumed at any time of the day, especially with
zelnik Zelnik is a traditional pastry eaten in Bulgaria and North Macedonia. It is composed of layers of thinly-rolled leavened wheat flour dough, or possibly phyllo pastry, filled with various combinations of sirene (a white cheese), feta cheese, egg ...
/zeljanica, burek and
banitsa Banitsa ( bg, баница, , also transliterated as banica and banitza) is a traditional pastry dish made in Bulgaria, North Macedonia and Southeastern Serbia (where it may also be referred to as gibanica), prepared by layering a mixture of whi ...
/
gibanica Gibanica ( sr-cyr, Гибаница, ) is a traditional pastry dish popular all over the Balkans. It is usually made with cottage cheese and eggs. Recipes can range from sweet to savoury, and from simple to festive and elaborate multi-layered ...
, as well as in cold soups served in the summer.


Origin and etymology

The word ''kefir'', known in Russian language and Eastern-European countries since at least 1884, is of Turkic and North Caucasian origin, it comes from Russian probably ultimately from Old Turkic ''köpür'' ''(milk) froth, foam'' ''from'' ''köpürmäk'' ''to froth.'' Traditional kefir was made in goatskin bags that were hung near a doorway; the bags would be knocked by anyone passing through to keep the milk and kefir grains well mixed. In
Karachay-Balkar Karachay-Balkar (, ), or Mountain Turkic (, ), is a Turkic language spoken by the Karachays and Balkars in Kabardino-Balkaria and Karachay–Cherkessia, European Russia, as well as by an immigrant population in Afyonkarahisar Province, Turkey. I ...
gıpı, which has connection with gıbıt (
wineskin A wineskin is an ancient type of bottle made of leathered animal skin, usually from goats or sheep, used to store or transport wine. History Its first mentions come from Ancient Greece, where, in the parties called Bacchanalia, dedicated to t ...
). It was under the name "wineskin" that Karachay kefir was distributed in the second half of the 19th century and at the beginning of the 20th century. Kefir spread from the former Soviet Union to the rest of
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, and the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
by the early 21st century. It has become known in parts of
Latin America Latin America or * french: Amérique Latine, link=no * ht, Amerik Latin, link=no * pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived f ...
as ''búlgaros'', or "
Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...
ns". The homeland of kefir is considered to be "the vicinity of
Elbrus Mount Elbrus ( rus, links=no, Эльбрус, r=Elbrus, p=ɪlʲˈbrus; kbd, Ӏуащхьэмахуэ, 'uaşhəmaxuə; krc, Минги тау, Mingi Taw) is the highest and most prominent peak in Russia and Europe. It is situated in the we ...
along the upper reaches of the
Kuban Kuban (Russian language, Russian and Ukrainian language, Ukrainian: Кубань; ady, Пшызэ) is a historical and geographical region of Southern Russia surrounding the Kuban River, on the Black Sea between the Pontic–Caspian steppe, ...
". Irina Timofeevna Sakharova was the first Russian food and dairy worker who learned the secret of making kefir from a Karachay rich man, having visited the estate of a rich Karachay uzden Bekmyrza Baychorov, brought kefir fungi from Narsana to
Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 million ...
.


Fermentation

Traditional kefir is fermented at ambient temperatures, generally overnight. Fermentation of the lactose yields a sour, carbonated, slightly alcoholic beverage, with a consistency and taste similar to drinkable
yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial Fermentation (food), fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in t ...
. The kefir grains initiating the fermentation are initially created by auto-aggregations of ''
Lactobacillus kefiranofaciens ''Lactobacillus kefiranofaciens'' is a species of slime-forming, homofermentative, rod-shaped lactic acid bacteria first isolated from kefir grains, hence its name. Its type strain is WT-2B (ATCC 43761). Its genome has been sequenced. References ...
'' and ''
Saccharomyces turicensis ''Saccharomyces'' is a genus of fungi that includes many species of yeasts. ''Saccharomyces'' is from Greek σάκχαρον (sugar) and μύκης (fungus) and means ''sugar fungus''. Many members of this genus are considered very important in f ...
'', where multiple biofilm producers cause the surfaces to adhere which form a three dimensional microcolony. The biofilm is a
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
of heteropolysaccharides called kefiran, which is composed of equal proportions of
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
and galactose. It resembles small
cauliflower Cauliflower is one of several vegetables in the species ''Brassica oleracea'' in the genus ''Brassica'', which is in the Brassicaceae (or mustard) family. It is an annual plant that reproduces by seed. Typically, only the head is eaten – the ...
grains, with color ranging from white to creamy yellow. A complex and highly variable symbiotic community can be found in these grains, which can include acetic acid bacteria (such as ''A. aceti'' and ''A. rasens''), yeasts (such as '' Candida kefyr'' and ''S. cerevisiae'') and a number of ''Lactobacillus'' species, such as ''L. parakefiri'', ''L. kefiranofaciens'' (and subsp. ''kefirgranum''), ''L. kefiri'', etc. While some microbes predominate, '' Lactobacillus'' species are always present. The microbe flora can vary between batches of kefir due to factors such as the kefir grains rising out of the milk while fermenting or curds forming around the grains, as well as temperature. Additionally, Tibetan kefir composition differs from that of the Russian kefir, Irish kefir, Taiwan kefir and Turkey
fermented beverage This is a list of fermented foods, which are foods produced or preserved by the action of microorganisms. In this context, fermentation typically refers to the fermentation of sugar to alcohol using yeast, but other fermentation processes involv ...
with kefir. In recent years, the use of freeze-dried starter culture has become common due to stability of the fermentation result, because the species of microbes are selected in laboratory conditions, as well as easy transportation. During fermentation, changes in the composition of ingredients occur.
Lactose Lactose is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from ' (gen. '), the Latin word for milk, plus the suffix '' - ...
, the sugar present in milk, is broken down mostly to
lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
(25%) by the lactic acid bacteria, which results in acidification. Propionibacteria further break down some of the lactic acid into
propionic acid Propionic acid (, from the Greek words πρῶτος : ''prōtos'', meaning "first", and πίων : ''píōn'', meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula CH3CH2CO2H. It is a liq ...
(these bacteria also carry out the same fermentation in
Swiss cheese Swiss cheese may refer to: Cheese * List of Swiss cheeses (from Switzerland) * Swiss-type cheeses or Alpine cheeses, a class of cooked pressed cheeses now made in many countries * Swiss cheese (North America), any of several related varieties o ...
). Other substances that contribute to the flavor of kefir are
pyruvic acid Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...
,
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
, diacetyl and
acetoin Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, is an organic compound with the formula CH3CH(OH)C(O)CH3. It is a colorless liquid with a pleasant, buttery odor. It is chiral. The form produced by bacteria is (''R'')-acetoin. ...
(both of which contribute a "buttery" flavor),
citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...
,
acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...
, and
amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
resulting from protein breakdown.


Decreased lactose content

During the fermentation process, bacteria and yeast break lactose down into glucose and galactose. As a result of the fermentation, lactose levels are decreased by 20–30% with respect to the initial lactose levels present in the milk. One study found that when people with lactose intolerance consumed the same amount of lactose in milk, kefir or yoghurt products, the latter two significantly reduced symptoms of lactose intolerance during the first 8 hours after consumption. This result suggests that yoghurt and kefir might be suitable for people with lactose intolerance. However, the long-term impact of kefir consumption on lactose intolerance has not been studied. It has also been shown that fermented milk products have a slower transit time than milk, which may further improve lactose digestion.


Alcohol content

Kefir contains
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
, which is detectable in the blood of human consumers. The level of ethanol in kefir can vary by production method. A 2016 study of kefir sold in Germany showed an ethanol level of only 0.02 g per litre, which was attributed to fermentation under controlled conditions allowing the growth of ''Lactobacteria'' only, but excluding the growth of other microorganisms that form much higher amounts of ethanol. A 2008 study of German commercial kefir found levels of 0.002-0.005% of ethanol. Kefir produced by small-scale dairies in Russia early in the 20th century had 1-2% ethanol. Modern processes, which use shorter fermentation times, result in much lower ethanol concentrations of 0.2–0.3%.


Nutrition


Composition

Kefir products contain nutrients in varying amounts from negligible to significant, including
dietary mineral In the context of nutrition, a mineral is a chemical element required as an essential nutrient by organisms to perform functions necessary for life. However, the four major structural elements in the human body by weight (oxygen, hydrogen, carbon ...
s,
vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, essential micronutrient that an organism needs in small quantities for the proper functioning of its ...
s, essential amino acids, and
conjugated linoleic acid Conjugated linoleic acids (CLA) are a family of isomers of linoleic acid. In principle, 28 isomers are possible. CLA is found mostly in the meat and dairy products derived from ruminants. The two C=C double bonds are conjugated (i.e., separated ...
, in amounts similar to unfermented cow, goat, or sheep milk. At a pH of 4.2 – 4.6, kefir is composed mainly of water and by-products of the fermentation process, including
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
and
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
. Typical of milk, several dietary minerals are found in kefir, such as
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
, iron,
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
,
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
,
potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
,
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
, copper,
molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
,
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
, and
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
in amounts that have not been standardized to a reputable nutrient database. Also similar to milk, kefir contains vitamins in variable amounts, including
vitamin A Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...
, vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B6 (pyridoxine), vitamin B9 (folic acid), vitamin B12 (cyanocobalamin),
vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
,
vitamin D Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...
, and
vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...
. Essential amino acids found in kefir include
methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical ro ...
,
cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...
,
tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...
,
phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino a ...
,
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...
, leucine,
isoleucine Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the deprot ...
,
threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), a carboxyl group (which is in the deprotonated −COO ...
,
lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −C ...
, and
valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deprotonat ...
, as for any milk product.


Microbiota

Probiotic Probiotics are live microorganisms promoted with claims that they provide health benefits when consumed, generally by improving or restoring the gut microbiota. Probiotics are considered generally safe to consume, but may cause bacteria-host i ...
bacteria found in kefir products include: ''
Lactobacillus acidophilus ''Lactobacillus acidophilus'' (New Latin 'acid-loving milk-bacillus') is a rod-shaped, Gram-positive, homofermentative, anaerobic microbe first isolated from infant feces in the year 1900. The species is most commonly found in humans, specifically ...
'', ''
Bifidobacterium bifidum ''Bifidobacterium bifidum'' is a bacterial species of the genus ''Bifidobacterium''. ''B. bifidum'' is one of the most common probiotic bacteria that can be found in the body of mammals, including humans. Structure and characteristics ''B. bifi ...
'', '' Streptococcus thermophilus'', ''
Lactobacillus delbrueckii subsp. bulgaricus ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' (until 2014 known as ''Lactobacillus 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. ...
'', '' Lactobacillus helveticus'', ''
Lactobacillus kefiranofaciens ''Lactobacillus kefiranofaciens'' is a species of slime-forming, homofermentative, rod-shaped lactic acid bacteria first isolated from kefir grains, hence its name. Its type strain is WT-2B (ATCC 43761). Its genome has been sequenced. References ...
'', '' Lactococcus lactis'', and '' Leuconostoc'' species.
Lactobacilli The ''Lactobacillaceae'' are a family of lactic acid bacteria. It is the only family in the lactic acid bacteria which includes homofermentative and heterofermentative organisms; in the ''Lactobacillaceae,'' the pathway used for hexose fermentati ...
in kefir may exist in concentrations varying from approximately 1 million to 1 billion
colony-forming unit In microbiology, colony-forming unit (CFU, cfu or Cfu) is a unit which estimates the number of microbial cells (bacteria, fungi, viruses etc.) in a sample that are viable, able to multiply via binary fission under the controlled conditions. Cou ...
s per milliliter, and are the bacteria responsible for the synthesis of the polysaccharide ''kefiran''. In addition to bacteria, kefir often contains strains of
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
that can metabolize lactose, such as ''
Kluyveromyces marxianus ''Kluyveromyces marxianus'' in ascomycetous yeast and member of the genus, ''Kluyveromyces''. It is the sexual stage of '' Atelosaccharomyces pseudotropicalis'' also known as '' Candida kefyr''. This species has a homothallic mating system and ...
'', ''
Kluyveromyces lactis ''Kluyveromyces lactis'' is a ''Kluyveromyces'' yeast commonly used for genetic studies and industrial applications. Its name comes from the ability to assimilate lactose and convert it into lactic acid. ''Kluyveromyces lactis'' (formerly ''Sa ...
'', and ''
Saccharomyces ''Saccharomyces'' is a genus of fungi that includes many species of yeasts. ''Saccharomyces'' is from Greek σάκχαρον (sugar) and μύκης (fungus) and means ''sugar fungus''. Many members of this genus are considered very important in f ...
fragilis'', as well as strains of yeast that do not metabolize lactose, including ''
Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...
'', ''
Torulaspora delbrueckii ''Torulaspora delbrueckii'' is a ubiquitous yeast species with both wild and anthropic habitats. The type strain of ''T. delbrueckii'' is CBS 1146T, equivalent to CLIB 230 or ATCC 10662etc. The type strain of ''T. delbrueckii'' CBS 1146 T was seq ...
'', and '' Kazachstania unispora''. The nutritional significance of these strains is unknown.


Production

Modern kefir is made by adding kefir grains to milk typically at a proportion of 2–5% grains-to-milk. The mixture is then placed in a corrosion-resistant container, such as a glass jar, and stored preferably in the dark to prevent degradation of light-sensitive vitamins. After a period between 12 and 24 hours of fermentation at mild temperature, ideally 20–25 °C (68–77 °F), the grains are strained from the milk using a corrosion-resistant (stainless steel or plastic) utensil and kept to produce another batch. During the fermentation process the grains enlarge and eventually split forming new units. The resulting fermented liquid may be drunk, used in recipes, or kept aside in a sealed container for additional time to undergo a secondary fermentation. Because of its acidity the beverage should not be stored in reactive metal containers such as aluminium, copper, or zinc, as these may leach into it over time. The shelf life, unrefrigerated, is up to thirty days. The Russian method permits production of kefir on a larger scale and uses two fermentations. The first step is to prepare the cultures by inoculating milk with 2–3% grains as described. The grains are then removed by filtration and 1–3% of the resulting liquid mother culture is added to milk and fermented for 12 to 18 hours. Kefir can be made using freeze-dried cultures commonly available in powder form from
health food store A health food store (or health food shop) is a type of grocery store that primarily sells health foods, organic foods, local produce, and often nutritional supplements. Health food stores typically offer a wider or more specialized selection of fo ...
s. A portion of the resulting kefir can be saved to be used a number of times to propagate further fermentations but ultimately does not form grains. In Taiwan, researchers were able to produce kefir in laboratory using microorganisms isolated from kefir grains. They report that the resulting kefir drink had chemical properties similar to homemade kefir.


Milk types

Kefir grains will ferment the milk from most mammals and will continue to grow in such milk. Typical animal milks used include cow, goat, and sheep, each with varying organoleptic (flavor, aroma, and texture) and nutritional qualities. Raw milk has been traditionally used. Milk sugar is not essential for the synthesis of the polysaccharide that makes up the grains (kefiran), and rice hydrolysate is a suitable alternative medium. Additionally, kefir grains will reproduce when fermenting soy milk, although they will change in appearance and size due to the differing proteins available to them. A variation of kefir grains that thrive in sugary water also exists, see
water kefir Tibicos, or water kefir, is a traditional fermented drink made with water and a symbiotic culture of bacteria and yeasts (SCOBY) held in a polysaccharide biofilm matrix created by the bacteria. It is sometimes consumed as an alternative to mil ...
(or ''tibicos''), and can vary markedly from milk kefir in both appearance and microbial composition.


Culinary

As it contains ''Lactobacillus'' bacteria, kefir can be used to make a
sourdough Sourdough or sourdough bread is a bread made by the fermentation of dough using wild lactobacillaceae and yeast. Lactic acid from fermentation imparts a sour taste and improves keeping qualities. History In the ''Encyclopedia of Food Microbio ...
bread. It is also useful as a
buttermilk Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream. As most modern butter in western countries is not made with cultured cream but uncultured sweet cream, most mod ...
substitute in
baking Baking is a method of preparing food that uses dry heat, typically in an oven, but can also be done in hot ashes, or on hot stones. The most common baked item is bread but many other types of foods can be baked. Heat is gradually transferred " ...
. Kefir is one of the main ingredients in cold borscht soup in
Lithuania Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...
, also known in Poland as ''Lithuanian cold soup'' (''chłodnik litewski''), and other countries. Kefir-based soup okroshka is common across the former
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
. Kefir may be used in place of milk on cereal, granola,
milkshakes A milkshake (sometimes simply called a shake) is a sweet beverage made by blending milk, ice cream, and flavorings or sweeteners such as butterscotch, caramel sauce, chocolate syrup, fruit syrup, or whole fruit into a thick, sweet, cold mixture ...
,
salad A salad is a dish consisting of mixed, mostly natural ingredients with at least one raw ingredient. They are typically served at room temperature or chilled, though some can be served warm. Condiments and salad dressings, which exist in a va ...
dressing,
ice cream Ice cream is a sweetened frozen food typically eaten as a snack or dessert. It may be made from milk or cream and is flavoured with a sweetener, either sugar or an alternative, and a spice, such as cocoa or vanilla, or with fruit such as str ...
,
smoothies A smoothie is a beverage made by puréeing ingredients in a blender. A smoothie commonly has a liquid base, such as fruit juice or milk, yogurt, ice cream or cottage cheese. Other ingredients may be added, including fruits, vegetables, non-dai ...
and
soup Soup is a primarily liquid food, generally served warm or hot (but may be cool or cold), that is made by combining ingredients of meat or vegetables with stock, milk, or water. Hot soups are additionally characterized by boiling solid ing ...
.


See also

*
List of yogurt-based dishes and beverages This is a list of yogurt-based dishes and beverages. Yogurt is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as "yogurt cultures". Fermentation of lactose by these bacteria produces lactic acid, w ...


Other fermented dairy products

* Airag *
Amasi Amasi (in Zulu and Xhosa), maas (in Afrikaans), or mafi (in Sesotho), is a fermented milk product that is similar to cottage cheese or plain yogurt. It is a popular snack in South Africa and Lesotho. Preparation Amasi is traditionally prep ...
* Ayran *
Buttermilk Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream. As most modern butter in western countries is not made with cultured cream but uncultured sweet cream, most mod ...
* Chaas *
Chalap Chalap or shalap or chalob ( ky, чалап, ; uz, chalob, ; kk, шалап, translit=shalap, ), also marketed as Tan ( ky, Тан, ) by Enesay ( ky, Энесай), is a beverage common to Kyrgyzstan and Kazakhstan. It consists of qatiq or suz ...
* Cheese * Cream cheese *
Doogh Ayran, doogh, dhallë, daw, xynogala or tan is a cold savory yogurt-based beverage popular across Western Asia, Central Asia, South Asia, Southeastern Europe, North Asia and Eastern Europe. The principal ingredients are yogurt, water and salt. ...
*
Filmjölk (), also known as , is a traditional fermented milk product from Sweden, and a common dairy product within the Nordic countries. It is made by fermenting cow's milk with a variety of bacteria from the species ''Lactococcus lactis'' and ''Leuconos ...
*
Kumis ''Kumis'' (also spelled ''kumiss'' or ''koumiss'' or ''kumys'', see other transliterations and cognate words below under terminology and etymology – otk, airag kk, қымыз, ''qymyz'') mn, айраг, ''ääryg'') is a fermented dairy p ...
* Leben * Labneh *
Lassi Lassi () is a regional name for buttermilk, the traditional dahi (yogurt)–based drink, consumed in the South Asian region. Lassi is a blend of yogurt, water, spices, and sometimes fruit. Salty lassi is similar to doogh, while modern sweet la ...
*
Matzoon Matzoon ( hy, մածուն, ''matsun'') or matsoni ( ka, მაწონი, ''mats'oni'') is a fermented milk product of Armenian origin, distributed in Armenia and Georgia. The so-called ''Caspian Sea yogurt'' circulated and commercialized in ...
*
Mursik Mursik is a traditional fermented milk variant of the Kalenjin people of Kenya. It can be made from cow or goat milk and is fermented in a specially made calabash gourd locally known as a ''sotet''. The gourd is lined with soot from specific trees ...
* Ryazhenka * *
Shubat Chal, or shubat ( kk, шұбат, ), is a Turkic (especially Turkmen, Uzbek and Kazakh) beverage of fermented camel milk, sparkling white with a sour flavor, popular in Central Asia — particularly in Kazakhstan, Uzbekistan and Turkmenistan. ...
* Skyr *
Varenets Varenets (russian: варенец, lit=the stewed one), sometimes anglicised as stewler or simmeler, is a fermented milk product that is popular in Russia. Similar to ryazhenka, it is made by adding sour cream (Smetana (dairy product), smetana) to ...
*
Viili Viili (Finnish) is a mesophilic fermented milk product found in the Nordic countries, particularly Finland. Viili is similar to yoghurt or kefir, but when left unmixed, its texture is malleable, or "long". The metabolism of the bacteria used in ...
*
Yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial Fermentation (food), fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in t ...


Other fermented beverages

* Boza * Tibicos ("Water Kefir") * Kombucha


References


External links


Fermented Foods: Kefir
from the National Center for Home Food Preservation * * {{Authority control Fermented dairy products Fermented drinks Milk-based drinks Russian drinks Russian desserts Sour foods Turkish drinks Ukrainian drinks Polish drinks