Kefir

Kefir
Plain kefir being poured
Alternative names Milk kefir, búlgaros
Main ingredients Milk, kefir grains (bacteria, yeasts, proteins, lipids, sugar)

Kefir or kephir (/kəˈfɪər/ kə-FEER),[1][2] alternatively milk kefir (to distinguish it from water kefir) or búlgaros, is a fermented milk drink made with a yeast/bacterial fermentation starter of kefir grains, that originated in the Caucasus Mountains of West Asia.[3] It is prepared by inoculating cow, goat, or sheep milk with kefir grains.[4] 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.[5]

Etymology

The word kefir, known in Russian since at least 1884,[6] is probably of Caucasian origin,[7] although some sources see a connection to Turkic köpür (foam)[7] or kef (a word of Persian origin meaning foam or bubbles). Kefir has become the most commonly used term, but other names are found in different geographic regions.

Overview

Kefir grains, a symbiotic culture of bacteria and yeasts

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 thin yogurt.[8]

The kefir grains initiating the fermentation are a combination of lactic acid bacteria and yeasts in a matrix of proteins, lipids, and sugars. This symbiotic culture of bacteria and yeast (or SCOBY) forms "grains" that resemble cauliflower. A complex and highly variable community of lactic acid bacteria and yeasts can be found in these grains, although some predominate; Lactobacillus species are always present.[3] Even successive batches of kefir may differ due to factors such as the kefir grains rising out of the milk while fermenting or curds forming around the grains, as well as room temperature.[9]

Kefir grains contain kefiran, a water-soluble polysaccharide, which imparts a creamy texture and feeling in the mouth. The grains range in color from white (the acceptable color of healthy grains) to yellow. The latter is the outcome of leaving the grains in the same milk during fermentation for longer than the optimal 24-hour period and continually doing so over many batches. Grains may grow to the size of walnuts or even larger.

The composition of kefir depends greatly on the type of milk that was fermented, including the concentration of vitamin B12.

During fermentation, changes in composition of nutrients and other ingredients occur. Lactose, the sugar present in milk, is broken down mostly to lactic acid (25%) by the lactic acid bacteria, which results in acidification of the product.[3] Propionibacteria further break down some of the lactic acid into propionic acid (these bacteria also carry out the same fermentation in Swiss cheese). A portion of lactose is converted to kefiran, which is indigestible by gastric digestion. Other substances that contribute to the flavor of kefir are pyruvic acid, acetic acid, diacetyl and acetoin (both of which contribute a "buttery" flavor), citric acid, acetaldehyde, and amino acids resulting from protein breakdown.[10]

Kefir production

The slow-acting yeasts, late in the fermentation process, break lactose down into ethanol and carbon dioxide. Depending on the process, ethanol concentration can be as high as 1–2% (achieved by small-scale dairies early in the 20th century), with the kefir having a bubbly appearance and carbonated taste. This makes kefir different from yogurt and most other sour milk products where only bacteria ferment the lactose into acids. Most modern processes, which use shorter fermentation times, result in much lower ethanol concentrations of 0.2–0.3%.

As a result of the fermentation, very little lactose remains in kefir. People with lactose intolerance are able to tolerate kefir, provided the number of live bacteria present in this beverage consumed is high enough (i.e., fermentation has proceeded for adequate time). It has also been shown that fermented milk products have a slower transit time than milk, which may further improve lactose digestion.[11]

For the preparation of commercially-prepared kefir, so-called mild kefir, kefir grains are no longer used, but rather a powdered preparation of bacteria and yeast, allowing the flavor to be kept constant.

Variations that thrive in various other liquids exist, and vary markedly from kefir in both appearance and microbial composition. Water kefir (or tibicos) is grown for a day or more at room temperature in water with sugar, sometimes with lemon juice and added dry fruit such as figs.

Nutrition

Nutritional composition

Kefir products contain nutrients in varying amounts from negligible to significant, including dietary minerals, vitamins, essential amino acids, and conjugated linoleic acid,[12] in amounts similar to unfermented cow, goat, or sheep milk.[13] At a pH of 4.2 - 4.6,[14] kefir is composed mainly of water and by-products of the fermentation process, including carbon dioxide and ethanol.[15]

Typical of milk, several dietary minerals are found in kefir, such as calcium, iron, phosphorus, magnesium, potassium, sodium, copper, molybdenum, manganese, and zinc in amounts that have not been standardized to a reputable nutrient database.[15] Also similar to milk,[13] kefir contains vitamins in variable amounts, including vitamin A, vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B6 (pyridoxine), vitamin B9 (folic acid), vitamin B12 (cyanocobalamin), vitamin C, vitamin D, and vitamin E.[15] Essential amino acids found in kefir include methionine, cysteine, tryptophan, phenylalanine, tyrosine, leucine, isoleucine, threonine, lysine, and valine,[15] as for any milk product.[13]

Probiotics

Probiotic bacteria found in kefir products include: Lactobacillus acidophilus, Bifidobacterium bifidum, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus helveticus, Lactobacillus kefiranofaciens, Lactococcus lactis, and Leuconostoc species.[3][12][16] Lactobacilli in kefir may exist in concentrations varying from approximately 1 million to 1 billion colony-forming units per milliliter, and are the bacteria responsible for the synthesis of the polysaccharide kefiran.[4]

In addition to bacteria, kefir often contains strains of yeast that can metabolize lactose, such as Kluyveromyces marxianus, Kluyveromyces lactis, and Saccharomyces fragilis, as well as strains of yeast that do not metabolize lactose, including Saccharomyces cerevisiae, Torulaspora delbrueckii, and Kazachstania unispora.[3] The nutritional significance of these strains is unknown.

Production

90 grams of kefir grains

Production of traditional kefir requires a starter community of kefir grains which are added to milk.

The traditional or artisanal method of making kefir is to add 2–10% kefir grains directly to milk in a sealed goatskin leather bag, which is traditionally agitated one or more times a day. Today the leather bag is replaced with a corrosion-resistant container such as a glass jar. It is not filled to capacity, allowing room for some expansion, as the carbon dioxide gas produced causes the liquid level to rise. Non-lightproof containers are stored in the dark to prevent degradation of light-sensitive vitamins. After a period of fermentation lasting around 24 hours, ideally at 20–25 °C (68–77 °F), the grains are strained from the liquid using a corrosion-resistant (stainless steel or plastic) utensil and kept as the starter for another batch.

The fermented liquid-kefir, which contains live micro-organisms from the grains, may be drunk, used in recipes, or kept aside in a sealed container for many days to undergo a slower secondary fermentation in which bio-synthesis by certain micro-organisms increases the content of folic acid and some other B vitamins, and the kefir becomes sourer. The shelf life, unrefrigerated, is up to thirty days.[17] The grains enlarge in the process of kefir production and eventually split.

The Russian method permits production of kefir on a larger scale and uses two fermentations. The first step is to prepare the cultures by incubating 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.[18]

Kefir can be made using freeze-dried cultures commonly available in powder form from health 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, so a fresh culture must be obtained.

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.

Kefir grains will also ferment milk substitutes such as soy milk, rice milk, nut milk and coconut milk, as well as other sugary liquids including fruit juice, coconut water, beer wort, and ginger beer. However, the kefir grains may cease growing if the medium used does not contain all the growth factors required by the bacteria.

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.[19] 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.[20]

Regional consumption

Kefir, first consumed in the Caucasus, Russia and Central Asian countries for centuries, spread to the rest of Europe, Japan, the United States by early 21st century.[21][22] In Chile, where it is known as "yogur de pajaritos" (little birds' yogurt), kefir has been regularly consumed for over a century.

Culinary uses

Lithuanian kefir-based borscht (šaltibarščiai)

As it contains Lactobacillus bacteria, kefir can be used to make a sourdough bread. It is also useful as a buttermilk substitute in baking. Kefir is one of the main ingredients in borscht in Lithuania, also known in Poland as Lithuanian cold soup (chłodnik litewski), and other countries.

Kefir-based soup okroshka is popular across the former Soviet Union.

Kefir may be used in place of milk on cereal, granola, milkshakes, soup, salad dressing, ice cream, smoothies and soup. [23]

Possible origin

Despite intensive research and many attempts to produce kefir grains from the pure or mixed cultures that are normally present in the grains, no successful results have been reported.[24]

See also

Other fermented dairy products

Other fermented beverages

References

  1. ↑ "kefir". Oxford Dictionaries.
  2. ↑ kefir. dictionary.reference.com
  3. 1 2 3 4 5 de Oliveira Leite AM, Miguel MA, Peixoto RS, Rosado AS, Silva JT, Paschoalin VM (October 2013). "Microbiological, technological and therapeutic properties of kefir: a natural probiotic beverage". Braz J Microbiol. 44 (2): 341–9. doi:10.1590/S1517-83822013000200001. PMC 3833126. PMID 24294220.
  4. 1 2 Altay F, Karbancıoglu-Güler F, Daskaya-Dikmen C, Heperkan D (October 2013). "A review on traditional Turkish fermented non-alcoholic beverages: microbiota, fermentation process and quality characteristics". Int J Food Microbiol. 167 (1): 44–56. doi:10.1016/j.ijfoodmicro.2013.06.016. PMID 23859403.
  5. ↑ Prescott; Harley; Klein. Microbiology (7th ed.). London: McGraw–Hill. p. 1040. ISBN 978-0-07-110231-5.
  6. ↑ "Origin of KEFIR". Merriam-Webster Dictionary Online.
  7. 1 2 "The American Heritage® Dictionary of the English Language – kefir".
  8. ↑ Kowsikowski, F. and Mistry, V. (1997). Cheese and Fermented Milk Foods, 3rd ed, vol. I. F. V. Kowsikowski, Westport, Conn., ISBN 0-9656456-0-6.
  9. ↑ Veronique Ninane; Gilbert Berben; Jean-Michel Romne; Robert Oger (2005). "Variability of the microbial abundance of kefir grain starter cultivated in partially controlled conditions" (PDF). Biotechnologie, Agronomie, Société et Environnement. 5 (3): 191–194. Archived from the original (PDF) on 2010-02-16.
  10. ↑ Handbook of Fermented Functional foods. 2nd Ed. Edward R. Farnsworth, Editor. CRC Press, 2008.
  11. ↑ Farnworth, Edward R. (2005). "Kefir – a complex probiotic" (PDF). Food Science & Technology Bulletin: Functional Foods. 2 (1): 1–17. doi:10.1616/1476-2137.13938. Archived from the original (PDF) on 2013-10-29.
  12. 1 2 Guzel-Seydim ZB, Kok-Tas T, Greene AK, Seydim AC (March 2011). "Review: functional properties of kefir". Crit Rev Food Sci Nutr. 51 (3): 261–8. doi:10.1080/10408390903579029. PMID 21390946.
  13. 1 2 3 "Nutrition facts for fluid sheep milk, one US cup, 245 ml". Conde Nast, Nutritiondata.com, USDA Nutrient Database, Standard Reference, version 21. 2014. Retrieved 19 November 2014.
  14. ↑ Odet (1995). "Fermented Milks". IDF Bull. 300: 98–100.
  15. 1 2 3 4 Ahmed Z, Wang Y, Ahmad A, Khan ST, Nisa M, Ahmad H, Afreen A (2013). "Kefir and health: a contemporary perspective". Crit Rev Food Sci Nutr. 53 (5): 422–34. doi:10.1080/10408398.2010.540360. PMID 23391011.
  16. ↑ Farnworth, Edward R (4 April 2005). "Kefir-a complex probiotic" (PDF). Food Science and Technology Bulletin: Functional Foods. 2 (1): 1–17. doi:10.1616/1476-2137.13938. Archived from the original (PDF) on 14 May 2014. Retrieved 20 December 2014.
  17. ↑ Motegi; Mazaheri, M.; Moazami, N.; Farkhondeh, A.; Fooladi, M.H.; Goltapeh, E.M.; et al. (1997). "Kefir production in Iran" (PDF). World Journal of Microbiology & Biotechnology. 13 (5): 579–581. doi:10.1023/A:1018577728412. Archived from the original (PDF) on December 1, 2008.
  18. ↑ "Fabrication of kefir". Archived from the original on 12 November 2013. Retrieved 12 November 2013.
  19. ↑ Maeda, H; Zhu, X; Suzuki, S; Suzuki, K; Kitamura, S (2004-08-25). "Structural characterization and biological activities of an exopolysaccharide kefiran produced by Lactobacillus kefiranofaciens WT-2B(T)". Journal of Agricultural and Food Chemistry. American Chemical Society. 52 (17): 5533–8. doi:10.1021/jf049617g. PMID 15315396. Retrieved 2007-06-10.
  20. ↑ Abraham, Analía G.; de Antoni, Graciela L. (May 1999). "Characterization of kefir grains grown in cows' milk and in soy milk". Journal of Dairy Research. Cambridge University Press. 66 (2): 327–333. doi:10.1017/S0022029999003490. PMID 10376251. Retrieved 2007-06-09.
  21. ↑ Sando, Lillian (September 2015). "Kefir Consumption—a Growing Culture". International Milk Genomics Consortium. Retrieved 19 August 2017.
  22. ↑ Arslan, Seher (26 November 2014). "A review: chemical, microbiological and nutritional characteristics of kefir". CyTA – Journal of Food. 13 (3): 340–345. doi:10.1080/19476337.2014.981588.
  23. ↑ Milk Kefir from Cultures for Health. Cultures for Health. 2013. p. 89.
  24. ↑ Chen, T.-H.; Chen, M.-J.; Chen, K.-N.; Liu, J.-R.; Chen, M.-J. (2009). "Microbiological and chemical properties of kefir manufactured by entrapped microorganisms isolated from kefir grains" (PDF). Journal of Dairy Science. 92 (7): 3002–3013. doi:10.3168/jds.2008-1669. PMID 19528577.

Further reading

  • Katz, Sandor Ellix (2003). Wild Fermentation: The Flavor, Nutrition, and Craft of Live-Culture Foods. Chelsea Green Publishing Company. ISBN 1-931498-23-7.
  • Margulis, Lynn. Sex, Death and Kefir; August 1994; Scientific American, p. 96.
  • Margulis, Lynn. From Kefir to Death, Dazzle Gradually, 2007, p. 70.
  • Fermented Foods: Kefir, from the National Center for Home Food Preservation
  •  "Kephir". Collier's New Encyclopedia. 1921.
  •  "Kephir". New International Encyclopedia. 1905.
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