Kombucha

Kombucha is brewed tea plus sugar, taken over by a mixed culture — yeast and bacteria living together in the liquid and in a cellulose mat often called a SCOBY. MSU names black tea, sugar, and that culture as the main parts ¹. CSU: yeasts split sucrose toward glucose and fructose and make ethanol and carbon dioxide; acetic acid bacteria (they highlight Komagataeibacter / Gluconacetobacter) oxidize ethanol toward acetic acid and build the cellulose pellicle. Lactic acid bacteria can be in the mix; they are not the whole story ². This is Fermentation of tea, not grape wine and not cabbage Lacto-fermentation.

The drink belongs in Drinks, not in a preserving crock. Acidity is both flavor and a control: the pH falls as acids accumulate.

Alcohol is a real line, not a vibe #

Yeast makes ethanol. Bacteria can eat some of it. After bottling, without oxygen, remaining yeast can keep working and raise both carbonation and alcohol. CSU: that post-bottle ferment is capable of pushing the drink above 0.5 percent alcohol by volume ².

NC State Extension, restating federal alcohol rules: a product at 0.5 percent ABV or more is an alcohol beverage under the IRC. That includes kombucha bottled under 0.5 percent that later ferments past the line. Crossing 0.5 percent, even if you later strip alcohol back down, still requires TTB qualification. Below that threshold at all times, TTB’s alcohol rules generally do not apply and FDA food labeling does — unless the formula is a malt beverage (malted barley and hops), in which case beer rules can attach. TTB may class an alcoholic kombucha as beer or wine from the formula; NC State expects most to fall in those two ³. Beer and Cider are those identity cousins, not recipes to copy onto tea.

Post-bottle alcohol and pressure depend on the remaining sugar, yeast, temperature, and time; a safe process requires measurement and control.

What to notice (and when to stop) #

Watch Acidity, not a lifestyle clock. MSU: pH starts around 5 or higher and moves toward about 2.5 over 7 to 10 days; they say discard if 2.5 is not reached by day 10. Use a meter or strips; smell vinegar-sharp tea, not rot. Mold, odd color, or fuzzy growth on the culture: throw the culture and the liquid away ¹. CSU’s retail-oriented control is a different clock: pH from about 5 to 4.2 within seven days, then toward an endpoint around 2.5; failure to hit 4.2 in a week they treat as a bad culture or a too-cold ferment ². Those are two extension instructions. Do not average them into a third number.

MSU: low pH argues for glass (or other food-grade) vessels; some metals can leach. Hygiene still matters — acid is not a substitute for dirt ¹. Food safety owns the general contamination problem.

Health claims do not replace acidity, hygiene, or pressure control. Kombucha belongs with Drinks.