Kefir

Kefir or kephir (/kəˈfɪər/ kə-FEER), 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 Caucasus, Eastern Europe and Russia, where it is prepared by inoculating cow, goat, or sheep milk with kefir grains. Kefir or kephir (/kəˈfɪər/ kə-FEER), 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 Caucasus, Eastern Europe and Russia, where it is prepared by inoculating cow, goat, or sheep milk with kefir grains. The word kefir, known in Russian since at least 1884, is probably of Caucasian origin, although some sources see a connection to Turkic köpür (foam) or kef (a Kurdish word meaning foam or bubbles) . 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. Kefir spread from the former Soviet Union to the rest of Europe, Japan, the United States by the early 21st century. It has become known in Latin America as búlgaros, or 'Bulgarian drink'. 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. The kefir grains initiating the fermentation consist of a symbiotic culture of lactic acid bacteria and yeasts embedded in a matrix of proteins, lipids, and polysaccharides. The matrix is formed by microbial activity and resemble small cauliflower grains, with color ranging from white to creamy yellow. A complex and highly variable community can be found in these grains, which can include lactic acid bacteria, acetic acid bacteria, and yeasts. 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. During fermentation, changes in the composition of 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. Propionibacteria further break down some of the lactic acid into propionic acid (these bacteria also carry out the same fermentation in Swiss cheese). 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. 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. Kefir products contain nutrients in varying amounts from negligible to significant, including dietary minerals, vitamins, essential amino acids, and conjugated linoleic acid, 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 and ethanol. 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. Also similar to milk, 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. Essential amino acids found in kefir include methionine, cysteine, tryptophan, phenylalanine, tyrosine, leucine, isoleucine, threonine, lysine, and valine, as for any milk product.