The Science of Kefir: Advances in Microbial Ecology, Bioprocess Control, and Functional Health Outcomes

Kefir is a traditional fermented beverage produced by the metabolic cooperation of lactic acid bacteria, acetic acid bacteria and yeasts within a kefiran matrix. This microbial diversity shapes its distinctive sensory and therapeutic properties and has established kefir as a model system in microbial ecology and biotechnology. Guided by the PRISMA framework, this review combines bibliometric analysis with a synthesis of recent work on kefir community dynamics. Metabolic cross-feeding and functional redundancy sustain the stability of this self-organizing ecosystem. The shift from dairy substrates to plant-based matrices is examined in relation to reported health effects, including gut microbiome modulation, immune regulation and antimicrobial activity. Concerns over safety and standardization in spontaneous fermentation have encouraged the development of defined synthetic microbial consortia (SynComs) and controlled bioreactor systems. Emerging tools, including AI-assisted bioprocessing and digital-twin modelling, further position kefir as a model for microbiome-inspired precision biotechnology.