Kefir is considered a nutritious drink suitable for inclusion in special diets and in the therapy of gastrointestinal disorders. Kefir is very similar to cultured buttermilk, yogurt and any other fermented milk. The gross composition and caloric value are very similar to that of milk, except that about one-quarter of the 5 percent lactose will have been converted to lactic acid. This will be of benefit to lactose-intolerant persons. Furthermore, the bacteria contained in the kefir will provide lactase, the enzyme in short supply in lactose-intolerant individuals. In addition, kefir contains 0.01 to 0.1 percent ethanol and 1 percent titratable acidity.

Wherever available in the world, kefir is considered an aid in the therapy of gastro-intestinal disorders. Evidence of success in such treatment is largely based on centuries of anecdotal observations. Kefir organisms have not been widely studied, and controlled studies with kefir and consumers have not been conducted. The organisms that have received the most attention by health scientists are Lactobacillus acidophilus and Bifidobacterium bifidum. These organisms appear to have several effects including: better lactose digestion, control of pathogenic or otherwise undesirable intestinal microorganisms, reduction in blood serum cholesterol, reduction in colon carcinogens, and immune system stimulation to resist infections.

Manufacture

Traditional kefir is manufactured using kefir "grains," which are porous polysaccharide structures resembling small cauliflower florets; the grains hold the microorganisms that are responsible for the fermentation process. The microflora in the grains include lactic acid streptococci, leuconostocs, lactobacilli, yeasts and acetic acid bacteria. After fermentation, 1 mL of good quality kefir contains 104 to 109 microbes.

Kefir is made from whole, low-fat or skim milk. Because of a lower fat content, body and mouthfeel of the final product may be lacking. Adjustments can be made by adding 1 to 4 percent non-fat milk solids (skim milk powder). The milk is pasteurized; excessive heat treatment, e.g., 95°C (203°F) for 10 to 15 minutes, will denature the whey proteins resulting in a subsequent stabilizing effect and better mouthfeel. The heat-treated milk is cooled to inoculation temperature (18-22°C, 64-72°F) and "kefir grains" are added at a rate of 2 to 5 percent. The milk is incubated for about 24 hours at 18-22°C with two intermittent stirrings. Then the kefir grains are sieved out, rinsed with cold tap water and added to a new lot of milk or saved for later use. The fermented product is chilled and ready for consumption.

When kefir grains are not removed from the fermented product, excessive acid production will gradually damage the live organisms. With refrigeration, acid production is inhibited, but the organisms will lose their activity after about 10 days. Several successive daily transfers may bring the culture (kefir grains) back to vitality. When kefir grains are washed with clean, cold water and dried on cloth or paper for 2 days at room temperature, they can then be stored in a dry, cool place for well over a year and still stay active. They can also be freeze-dried.

Summary and Conclusions

The entire field of fermented milks is replete with unanswered questions. Products such as kefir are burdened with myths, healing powers and other unproven beneficial effects. The folklore surrounding fermented milks is large and contradictory. If there ever was an area of food science in need of more research, this is it. Preliminary results of studies on probiotics and certain health benefits from lactic acid bacteria show great promise. The milk industry, consumers and society at large will be the ultimate beneficiaries.

References

Never, H. 1992. Analysis of kefir grain starter cultures by scanning electron microscopy. Milchwissenschaft 47(5):275- 278.

Kooman, P. 1968. The chemical structure of kefiran, the water- soluble polysaccharide of the kefir grain. Carbohydrate Research 7(2):200-211.

Kurmann, J.A., Rasic, J.L. and Kroger, M. 1992. Encyclopedia of Fermented Fresh Milk Products. Van Nostrand Reinhold, New York.

Koroleva, N.S. 1975. Microbiology of Whole Milk Products (in Russian). Pichchevoy Promyshlennosti, Moscow.

Kroger, M. 1993. Cultured Dairy Prod. 28(2):26-29.

Source: Cultured Dairy Products Journal, 1994.