What is kombucha? What it is made of, how it is made, and what is in a glass

Kombucha in one paragraph

Take black or green tea, dissolve sugar in it, and add a culture of bacteria and yeast along with some finished kombucha from a previous batch. Cover the jar with a cloth and leave it at room temperature. Over 7 to 14 days the culture transforms some of the sugar, the tea turns sour and slightly fizzy, and a rubbery disc of cellulose grows on the surface. Pour it off, and you have kombucha. That is the whole thing; everything else is detail.

The culture is the interesting part. It is a stable community of yeasts (Brettanomyces, Saccharomyces, Zygosaccharomyces and others) and acetic acid bacteria (Komagataeibacter, Acetobacter, Gluconobacter), often with some lactic acid bacteria. They depend on each other: the yeasts make alcohol the bacteria need, and the bacteria make the acidic environment that keeps competitors out. What a SCOBY is goes into how that partnership works.

How kombucha is made

The process has two stages. The first fermentation happens in an open jar under a cloth, with oxygen, and it is where the tea becomes kombucha: sugar down, acids up, culture growing. The second fermentation is optional and happens in sealed bottles, usually with a little fruit or juice, and it is where the fizz and most of the flavor come from. Then the bottles go in the fridge, which slows everything down.

At home the ingredients are just water, tea, sugar, and the culture, in a ratio of roughly 5 g of tea and 60 to 70 g of sugar per liter, with 10 to 20 percent starter liquid. Commercial producers do the same at scale, then often filter, flavor, and sometimes pasteurize or dilute the result to keep the alcohol and sugar within legal and label limits. How to make kombucha walks through the home version step by step.

What it tastes like

Young kombucha tastes like sweet tea with a sour edge. A balanced batch is tart, lightly sweet, faintly fizzy, and a little like a dry cider or a sour apple juice, with the tea still recognisable underneath. Left longer it heads toward vinegar. Black tea gives a fuller, rounder drink; green tea a lighter, grassier one. Flavored kombucha layers fruit, ginger, or herbs on top of that base, which is why the bottle in the shop can taste like anything from lemonade to a sour beer.

What is actually in a glass

The numbers below are for finished kombucha. They vary with the tea, the recipe, and above all the fermentation time, so treat them as ranges, not facts about your particular bottle.

The sugar, caffeine and calorie rows have their own guide, sugar, caffeine and calories in kombucha, and two more deserve one here. Alcohol, because it is the question people ask most and the one where home brewing differs most from the shop: does kombucha have alcohol? has the numbers. And the live microbes, because “contains live cultures” and “is a probiotic” are not the same claim: is kombucha good for you? looks at what the evidence supports.

Two things are not in the glass, despite what you may read: glucuronic acid in any meaningful amount (most analyses find little or none), and anything that “detoxifies”. Kombucha is a tart drink whose sugar content varies. That is enough.

Raw, pasteurized, hard, and other labels

• Raw or unpasteurized: bottled with the culture still alive. It has to be refrigerated, it keeps fermenting slowly, and it can grow a small pellicle in the bottle. This is the kind you can grow a SCOBY from.
• Pasteurized: heated to stop the culture. Shelf-stable, consistent, no live microbes, and no risk of the alcohol creeping up in the bottle.
• Hard kombucha: deliberately fermented or blended to 4–8% alcohol. An alcoholic drink that happens to start from kombucha.
• Jun: the same idea made with green tea and honey, using its own culture. Lighter, faster, and usually a bit more alcoholic.
• Kombucha concentrate, powders, and “kombucha flavored” drinks: usually not fermented tea at all. Read the ingredients.

How it compares to similar drinks

The closest relative is water kefir, another home ferment with grains you keep from batch to batch; many kombucha brewers run both. Milk kefir shares the “live culture” idea but is a dairy food. Prebiotic sodas are marketed next to kombucha but are not fermented at all.

Where kombucha comes from

The popular story places kombucha in Manchuria around 220 BC, as a tonic for a Qin emperor. There is no documentary evidence for that, and the name itself may come from a Japanese seaweed tea (konbu-cha) that has nothing to do with fermentation. What is documented is more modest and more recent: fermented tea cultures were being studied in Russia by the early 1900s, with the first known scientific description in 1913, and the drink spread through Germany and central Europe between the wars, sold in pharmacies as a health tonic under names like Kombuchaschwamm and Teepilz.

It stayed a home ferment passed between neighbours for most of the twentieth century, had a wave of popularity in the 1990s, and became a commercial category in the 2000s when bottled brands appeared in natural food shops and then supermarkets. The home brewing tradition never went away, which is why the culture in your jar is probably a descendant of one that has been shared, by hand, for generations.

Is it safe?

For most healthy adults, in normal amounts, yes. The acidity that makes kombucha taste the way it does is also what keeps it safe: a properly fermented batch reaches a pH that helps inhibit harmful bacteria, while clean handling still matters. The documented problems are rare and specific: mold on a home batch, brewing in lead-glazed ceramic, drinking large quantities of an extremely over-fermented brew, and contamination from poor hygiene. Home brewers avoid all of them with a few habits, which how to make kombucha and kombucha mold cover.

Frequently asked questions