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.
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.
Never, H. 1992. Analysis of kefir grain starter cultures by
scanning electron microscopy. Milchwissenschaft 47(5):275-
Kooman, P. 1968. The chemical structure of kefiran, the water-
soluble polysaccharide of the kefir grain. Carbohydrate
Kurmann, J.A., Rasic, J.L. and Kroger, M. 1992. Encyclopedia of
Fermented Fresh Milk Products. Van Nostrand Reinhold, New
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.