Pure cultures for making kefir

Lactobacilli (Lactobacillus delbrueckii subsp. bulgaricus HP1, L. helveticus MP12), Lactococcus lactis subsp. lactis C15, Streptococcus thermophilus T15 and yeasts (Saccharomyces cerevisiae A13) isolated from kefir grains were associated in a starter culture for kefir. Two procedures (simultaneous lactic acid and yeast fermentations for kefir A, and consecutive lactic acid and yeast fermentations for kefir B) were employed to reproduce the basic physicochemical and sensory characteristics of traditional kefir. During fermentation and maturation, kefirs with pure cultures were enriched with active cocci and lactobacilli (1011 cfu ml−1) and were regarded as a probiotic product. L. lactis subsp. lactis C15 and Streptococcus thermophilus T15 constituted the active part of the bacterial starter and the natural starter (kefir grains) in production of kefir A and traditional kefir. In kefir B the lactobacilli predominated nearly twice over the cocci. S. cerevisiae A13 produced singularly sufficient amounts of CO2 (1·98 g l−1) and alcohol (0·48%), which are major products in the formation of the typical yeasty flavour and aroma.