Kefir grains are a combination of bacteria and yeasts in a matrix of proteins, lipids, and sugars, and this symbiotic matrix forms “grains” that resemble cauliflower. For this reason, a complex and highly variable community of lactic acid bacteria and yeasts can be found in these grains.
Kefir grains contain a water soluble polysaccharide known as kefiran, which imparts a rope-like texture and feeling in the mouth; appear in hues ranging from white to yellow; and usually grow to the size of walnuts (although rice-grain-sized grains have been known to develop).
Traditional kefir is fermented at ambient temperatures, generally overnight. Fermentation of the lactose yields a sour, carbonated, slightly alcoholic beverage, with a consistency similar to thin yogurt.[4] Kefir fermented by small-scale dairies early in the 20th century achieved alcohol levels between 1 and 2 percent, but kefir made commercially with modern methods of production has less than 1% alcohol, possibly due to reduced fermentation time.[5]
Variations that thrive in various other liquids exist, and they vary markedly from kefir in both appearance and microbial composition. Water kefir (or kefir d’acqua) is grown in water with sugar (sometimes with added dry fruit such as figs, and lemon juice) for a day or more at room temperature.
Production of traditional kefir requires a starter community of kefir grains which are added to the liquid one wishes to ferment. Kefir grains cannot be produced from scratch, but the grains grow during fermentation, and additional grains are produced. Kefir grains can be bought from or donated by other growers.
The traditional, or artisanal, method of making kefir is achieved by directly adding kefir grains (2–10%) to milk in a loosely covered acid proof container which is traditionally agitated once or more times a day. It is not filled to capacity, allowing room for some expansion as the kefiran and carbon dioxide gas produced causes the liquid level to rise. If the container is not light proof it should be stored in the dark to prevent degradation of vitamins and inhibition of the culture. After a period of fermentation lasting around 24 hours, ideally at 20–25 °C (68–77 °F), the grains are removed from the liquid by sieving and reserved as the starter for a fresh amount of liquid. The temperature during fermentation is not critical as long as it is not above one that will kill the culture (about 40 °C / 104 °F), or much below 4 °C (39 °F) where the process will cease.
The fermented liquid which contains live microflora from the grain, may now be consumed as a beverage, used in recipes, or kept aside for several days to undergo a slower secondary fermentation which further thickens and sours the liquid. Without refrigeration the shelf life is two to three days. The grains will enlarge in the process of kefir production, and eventually split. Grains can be dried at room temperature or lyophilized (freeze-dried) or frozen.
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 grains (2–3%), as just described. The grains are then removed by filtration and the resulting liquid mother culture is added to milk (1–3%) which is fermented for 12 to 18 hours.
Kefir can be produced using lyophilized cultures commonly available as a POWDER FROM HEALTH FOOD SHOPS. 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, and a fresh culture must be obtained.
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