Kefir revisited: Insights from the North Caucasus.

Kefir is a probiotic fermented milk product, distributed throughout the world from the North Caucasus, formed by fermenting milk with kefir grains. Kefir grains represent a striking example of microbial symbiosis between bacteria and fungi. Despite the extensive shifts in microbial composition during milk fermentation, the composition of kefir grains remains relatively constant. The evolutionary origin of such a stable symbiont remains unclear. There are multiple reports of differences between commercial kefir-like products and kefir prepared according to traditional techniques by fermenting milk with indigenous kefir grains. Modern research is aimed at studying the health properties of kefir and kefir grain components. To accurately represent the evolutionary origin of kefir grains, the characteristics of important species or consortia for the development of new promising products, it is essential to study the composition of samples of historical kefir origin, particularly the Karachay-Cherkess and Kabardino-Balkarian Republics of the North Caucasus.