Water Kefir: Review of Microbial Diversity, Potential Health Benefits, and Fermentation Process

Water kefir is a non-dairy fermented beverage that ferments water kefir grains in a sucrose solution. These grains harbor a diverse microbiota, including lactic acid bacteria, acetic acid bacteria, and yeast species. The composition of water kefir is primarily influenced by cultivation conditions and the microbiota profile of the grains, resulting in fermentation metabolites such as ethanol, lactic acid, mannitol, acetic acid, glycerol, and other organic acids. However, this microbial diversity can vary depending on the origin of the grains, the fermentation substrate, and environmental conditions. As it is a potentially beneficial product for health, interest in kefir consumption has increased in recent years. Specific legislation for water kefir is still scarce, and despite potentially probiotic microorganisms, water kefir is not classified as a probiotic, but it fits the definition of a potentially functional food due to its health benefits. Studies demonstrate the potential health benefits of water kefir in terms of anti-inflammatory, antimicrobial, antioxidant, antidiabetic, and intestinal health effects. However, industrial-scale production and starter cultures have not yet been developed. This study aims to comprehensively review water kefir, exploring its potential health benefits, fermentation process, microbial diversity, and regulatory aspects.