The fermentation process used to make milk kefir is catalyzed by kefir grains. Kefir grains consist of a matrix of polysaccharides that contain a mixture of lactic acid bacteria, yeast, and acetic acid bacteria that all interact symbiotically with one another (1). The result of this fermentation is milk kefir, which played an instrumental role in helping me to achieve clinical remission from a severe case of inflammatory bowel disease in 2016.
Prado MR, Blandón LM, Vandenberghe LP, et al. Milk kefir: composition, microbial cultures, biological activities, and related products. Front Microbiol. 2015;6:1177. Published 2015 Oct 30. doi:10.3389/fmicb.2015.01177.