The dairy world offers yogurt and kefir, each governed by specific microbial partnerships. Yogurt is produced primarily by Lactobacillus bulgaricus and Streptococcus thermophilus working together at around 110°F (43°C) for 4–12 hours, after which the cultured milk thickens and tangs. Greek yogurt is achieved by straining off the whey, yielding a thicker product with concentrated protein. Culturing decisions shape flavor and function: traditional two-strain yogurts provide a classic tartness, while modern blends add additional strains for probiotic diversity. Cultivating can be open-ended—an heirloom yogurt can be perpetually re-cultured from a previous batch—or one-shot, with a direct-set packet of freeze-dried culture used only once. Kefir is a separate tradition, in which kefir grains—a symbiotic gelatinous colony of yeasts and bacteria—are added to milk to produce a tangier, slightly effervescent drink. The same approach with sugar water yields water kefir.
Kombucha is the most prominent beverage ferment outside the dairy case. It is brewed from sweet tea fermented by a SCOBY—a Symbiotic Culture of Bacteria and Yeast—over a primary fermentation of 7 to 14 days. The SCOBY itself grows in layered cellulose and acquires a thickness of roughly a quarter inch to an inch over repeated batches, with surplus layers stored in "SCOBY hotels" as backup cultures. Each batch produces a new SCOBY layer, which is thinned out periodically; the active culture also divides and grows with every brew. After the primary fermentation, many brewers perform a second fermentation by bottling the kombucha with fruit or flavorings, which produces natural carbonation. The resulting beverage contains about 0.5–2% alcohol by volume, well below most beers but sometimes noted on labels. Jun is a related drink that ferments green tea and honey rather than black tea and sucrose. Throughout this process, the sweet tea serves as fuel for the SCOBY, and the drink goes from sweet to tart as sugars are consumed and acids are produced.
Vinegar sits at the boundary between fermentation and oxidation. It is made by acetic acid bacteria (Acetobacter) that convert alcohol into acetic acid, a process that requires oxygen rather than the anaerobic conditions of most fermentations. Wild vinegars begin from fruit, wine, or cider left exposed to these bacteria, often forming a visible "mother"—a cellulose mat containing the bacteria and yeast—during 2–12 weeks of fermentation. Distinct regional vinegars—balsamic (aged Italian grape must), sherry (aged Spanish wine), malt (British barley), rice (East Asian fermented rice), and apple cider—are fundamentally variations on this core process. Vinegars may be diluted, sweetened, and used as drinking shrubs in cocktails and sodas. Unpasteurized vinegars retain living cultures, although commercial examples are usually filtered and heated to extend shelf life.