A study of methods to preserve kefir grains showed that grains stored at −20°C for
120 d had the same microflora profile and produced kefir with the same rheological
characteristics, acidity, and carbon dioxide content as kefir produced from nonstored
grains. Grains stored at 4°C and then used to inoculate milk produced inferior
quality kefir.71 Lyophilizing kefir grains has also been used as a way of producing
starter cultures for industrial production.72 However, a study of the properties of kefir
grains that had been lyophilized and then stored for 1–3 months in packages made
from films with different water and oxygen permeability showed that the rehydrated
grains were slower and less able to lower pH, produced less acidity, had decreasedlactose utilization, and a lower lactic acid production than fresh grains. The bacterial
profile of the rehydrated grains was also different than the fresh grains.73 This same
group compared freezing, refrigerating, air-drying, and lyophilization to preserve
kefir grains. They concluded after 10 months of storage that freezing and refrigeration
preserved acidification activity, whereas air-drying and lyophilization increased
lag phase and resulted in a lower initial rate of pH decrease.74
Traditionally, kefir grains have been replicated in cows’ milk. However, Abraham
and de Antoni11 have shown that the same grains that grow in cows’ milk can grow
and replicate in soybean milk. When soybean milk was used, the resulting grains
are more compact and smaller in size, and have a yellowish color—most likely due
to the protein. When the grains are added to the soybean milk, the pH is lower after
30 h than it is in cows’ milk. After 20 subcultures, the soybean-grown grains had a
higher protein content and lower polysaccharide content than the milk-grown grains,
although the microbial profiles of the two grains were similar.