Kefir is a common breakfast, lunch or dinner drink consumed in countries ofWest Asia andEastern Europe. Kefir is consumed at any time of the day, such as alongside European pastries likezelnik (zeljanica),burek andbanitsa/gibanica, as well as being an ingredient in cold soups.
Kefir has been found in graves in the Bronze AgeXiaohe Cemetery, dating back 3,600 years.[4]
The wordkefir, which is of North Caucasian origin,[5][6] became aninternational word, having originally spread to Russia, Central European and Eastern European countries at least by 1884.[7]
A Russian borrowing in English, its ultimate origin is unknown, though one theory is that the word comes fromköpür inOld Turkic.[6] More likely is another Caucasian origin; compareGeorgianკეფირი (k'epiri),Mingrelianქიფური (kipuri),Ossetianкъӕпы (k'æpy), andKarachay-Balkarгыпы (gıpı).
Traditional kefir was made ingoatskin 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.[8] In Karachay-Balkar,gıpı has a connection withgıpıt (wineskin). It was under the namewineskin that Karachay kefir was distributed in the second half of the 19th century and at the beginning of the 20th century.[9][10] Kefir spread from the former Soviet Union to the rest of Europe, Canada, Japan, and the United States by the early 21st century.[5][11][12] It has become known in parts ofLatin America asbúlgaros, or "Bulgarians".[citation needed]
Traditional kefir is fermented at ambient temperatures, generally overnight. Fermentation of the lactose yields asour,carbonated, slightly alcoholic beverage, with a consistency and taste similar to drinkableyogurt.[13]
The kefir grains initiating the fermentation are initially created by auto-aggregations ofLactobacillus kefiranofaciens andMaudiozyma turicensis[14] orM. humilis,[15] where multiplebiofilm producers cause the surfaces to adhere which form a three dimensional microcolony.[16][17][18] The biofilm is amatrix ofheteropolysaccharides called kefiran, which is composed of equal proportions ofglucose andgalactose.[5] It resembles smallcauliflower grains, with color ranging from white to creamy yellow. A complex and highly variable symbiotic community can be found in these grains, which can includeacetic acid bacteria (such asAcetobacter aceti andAcetobacter rasens), yeasts (such asCandida kefyr,K. lactis,K.marxianus,Saccharomyces cerevisiae,M. turicensis) and a number ofLactobacillus species, such asL. parakefiri,L. kefiranofaciens (and subsp.kefirgranum[19]),L. kefiri,[20]L. brevis[21], etc.[5] While some microbes predominate,Lactobacillus species are always present.[22] 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.[23] Additionally, Tibetan kefir composition differs from that of the Russian kefir, Irish kefir, Taiwan kefir and Turkeyfermented beverage with kefir.[5] In recent years, the use offreeze-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.[24][25][26]
During fermentation, changes in the composition of ingredients occur.Lactose, the sugar present in milk, is broken down mostly tolactic acid by the lactic acid bacteria, which results in acidification.[22]Propionibacteria further break down some of the lactic acid intopropionic acid (these bacteria also carry out the same fermentation inSwiss cheese). Other substances that contribute to the flavor of kefir arepyruvic acid,acetic acid,diacetyl andacetoin (both of which contribute a "buttery" flavor),citric acid,acetaldehyde, andamino acids resulting from protein breakdown.[27]
During the fermentation process, bacteria and yeast break lactose down into glucose and galactose.[28] As a result of the fermentation, lactose levels are decreased by 20–30% with respect to the initial lactose levels present in the milk.[29] One study found that when people withlactose intolerance consumed the same amount of lactose in milk, kefir oryogurt products, the latter two showed significantly reduced symptoms of lactose intolerance during the first 8 hours after consumption.[30] 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.[31]
Kefir contains a small amount ofethanol.[32] 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 ofLactobacteria only, but excluding the growth of other microorganisms that generate much higher amounts of ethanol.[33] A 2008 study of German commercial kefir found levels of 0.002–0.005% of ethanol.[34] Kefir produced by small-scale dairies in Russia in the early 20th century had 1–2% ethanol.[34]
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),[27] 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.[40]
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.[41]
Kefir can be made usingfreeze-dried cultures commonly available in powder form fromhealth food stores. 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.[citation needed]
In Taiwan, researchers were able to produce kefir in a laboratory using microorganisms isolated from kefir grains. They report that the resulting kefir drink had chemical properties similar to homemade kefir.[42]
Kefir grains will ferment the milk from mostmammals and will continue to grow in such milk. Typical animal milks used include cow, goat, and sheep, each with varyingorganoleptic (flavor, aroma, and texture) and nutritional qualities.Raw milk has been traditionally used.
Milk sugar is not essential for the synthesis of thepolysaccharide that makes up the grains (kefiran), and rice hydrolysate is a suitable alternative medium.[43] 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.[44]
A variation of kefir grains that thrive in sugary water also exists, seewater kefir (ortibicos), and can vary markedly from milk kefir in both appearance and microbial composition.[45]
^abAltay F, Karbancıoglu-Güler F, Daskaya-Dikmen C, et al. (October 2013). "A review on traditional Turkish fermented non-alcoholic beverages: microbiota, fermentation process and quality characteristics".International Journal of Food Microbiology.167 (1):44–56.doi:10.1016/j.ijfoodmicro.2013.06.016.PMID23859403.
^ab"kefir".Kefir dictionary definition | kefir defined.The American Heritage Dictionary of the English Language.Archived from the original on 18 April 2019. Retrieved11 December 2014.
^"Origin of KEFIR". Merriam-Webster Dictionary Online. 27 April 2023.Archived from the original on 18 April 2019. Retrieved15 October 2012.
^Wang SY, Chen KN, Lo YM, et al. (December 2012). "Investigation of microorganisms involved in biosynthesis of the kefir grain".Food Microbiology.32 (2):274–285.doi:10.1016/j.fm.2012.07.001.PMID22986190.
^Pidoux M (1 June 1989). "The microbial flora of sugary kefir grain (the gingerbeer plant): biosynthesis of the grain fromLactobacillus hilgardii producing a polysaccharide gel".MIRCEN journal of applied microbiology and biotechnology.5 (2):223–238.doi:10.1007/BF01741847.ISSN1573-0972.
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