Kefir is produced by adding either a starter culture called kefir grains directly or a
percolate of the grains to milk. Kefir grains are a mass of several different bacteria and
yeasts imbedded in a complex matrix of protein and carbohydrate. The microorganisms
in the kefir grains ferment the milk, and the grains can be recovered at the end of
the fermentation process. The grains have been described as resembling elastic small
florets similar to cauliflower in shape, yellow or white in color, and 20 to 30 mm in
size.9,10 Figure 4.1 is a photograph of kefir grains. A crude analysis of the grains shows
that they are a mass of bacteria, yeasts, polysaccharides, and proteins with a chemical
composition of 890 to 900 g/kg water, 2 g/kg lipid, 30 g/kg protein, 60 g/kg sugars,
and 7 g/kg ash.3 A study of the proteins in kefir grains using SDS-PAGE on acrylamide
gels indicated that the major grain proteins had a higher molecular weight than milk
proteins, indicating that they were not proteolysis products.1