Kombucha Brewing Calculator

Kombucha is a two-stage microbial conversion of sweetened tea rather than a single fermentation. Yeast invertase first splits sucrose into glucose and fructose; osmotolerant yeasts, commonly Brettanomyces, Zygosaccharomyces and Schizosaccharomyces species, ferment those sugars into ethanol and carbon dioxide. Acetic acid bacteria of the genus Komagataeibacter then oxidize the ethanol to acetic acid and convert glucose to gluconic acid. The floating tan pellicle usually called a SCOBY is bacterial cellulose secreted as a by-product, not the culture itself; most of the active organisms live suspended in the liquid. The customary charge is one cup of sugar, near 200 grams, per US gallon, which is roughly 50 grams per liter, with 5 to 8 grams of black tea per gallon supplying the nitrogen compounds and tannins the consortium needs. Starter liquid at 10 to 15 percent of batch volume matters more than any other variable, because it drops the starting pH below about 4.2 immediately and denies mold and spoilage bacteria a foothold. A finished primary brew typically lands between pH 2.5 and 3.5 with 5 to 10 grams per liter of total acids, reached in 7 to 14 days at 24 to 29 degrees C. Two caveats apply to any planning figure. The straight-line assumptions used here, a fixed share of sugar consumed per day and a steady pH decline, are approximations; real kinetics depend on temperature, tea strength, pellicle biomass and the surface-area-to-volume ratio of the vessel. Ethanol usually finishes between 0.2 and 1.5 percent ABV and can climb past the 0.5 percent US regulatory threshold during a sealed second fermentation.

Fermented sweet tea has a long folk history in Northeast China and Manchuria, from where it travelled along trade and rail routes into Russia and Eastern Europe. Russian sources describe it as chainyi grib, tea mushroom, and it was a common household drink there well before it reached Western Europe. The English name is a borrowing error: Japanese konbucha means kelp tea, an entirely different beverage, and the label attached to the tea ferment in early twentieth-century German writing and never came off. Because the tradition was domestic rather than industrial, no single inventor or founding date can be documented, and claims of precise ancient origins should be treated with caution. The science arrived independently of the folk practice. In 1886 A. J. Brown, working in Manchester, described the cellulose-forming organism he isolated from a vinegar plant, the bacterium now classified in Komagataeibacter and responsible for the kombucha pellicle. German physicians, notably Rudolf Sklenar in the 1950s and 1960s, popularized the drink for therapeutic use, spreading cultures by mail among hobbyists. Commercial bottling in the United States began in the mid-1990s, and a 2010 episode in which retailers pulled products after testing showed alcohol above the 0.5 percent limit forced the industry into routine alcohol testing, reformulation and clearer labeling. Later 16S rRNA sequencing surveys confirmed that the culture is a variable consortium, not a fixed organism, which is why results differ between households.