Microbiological and chemical changes during two-phase fermentation of kefir

Kefir is a fermented dairy product with the increasing interest for commercial production due to its benefits to human health. It is produced by the combination of alcoholic and lactic fermentation caused by the activity of kefir grains microbiota. Microbiological and chemical changes during the fermentation are driven by the activity of lactic acid bacteria and yeasts present in kefir grains. This paper describes the changes which occur during the kefir fermentation produced by the so-called "Russian method". In this two-phase fermentation, the increase in the number of lactic acid bacteria and yeast was observed. The activity of lactic acid bacteria led to the accumulation of organic acids and, consequently, to the pH value decrease. This process was followed by the lactose consumption, as the main energy source for microorganisms. On the other hand, yeasts present in the kefir culture induced the increase of the CO 2 content during both phases of fermentation. The application of this process can reduce the time needed for the kefir production without the reduction of its desirable sensory characteristics.