What is kombucha? Fermented tea and the culture behind it

What kombucha is

To brew kombucha, you add an active culture and sour starter liquid to cooled, sweetened black or green tea. A cloth cover lets air reach the brew while keeping insects out. As fermentation progresses, the tea becomes more acidic and a cellulose layer, called a pellicle, can grow at the surface. This layer is part of the culture; it isn’t the drink itself. The liquid is what you bottle, after checking fermentation and setting some aside to start the next batch.

SCOBY means symbiotic culture of bacteria and yeast. Researchers have identified yeasts such as Brettanomyces, Saccharomyces and Zygosaccharomyces, and acetic acid bacteria such as Komagataeibacter, Acetobacter and Gluconobacter. Some cultures also contain lactic acid bacteria, but the mix varies. Yeasts supply alcohol that acetic acid bacteria can use, and the resulting acids change the brew’s environment. The microbes live in the starter liquid as well as the pellicle. What a SCOBY is explains how to use and maintain that culture.

How kombucha is made

During the first fermentation, the jar stays covered with a breathable cloth. Oxygen allows acetic acid bacteria to work as the culture consumes sugar and produces acids. You can bottle and refrigerate the finished brew at this point. An optional second fermentation in sealed bottles traps carbon dioxide for more fizz, often with added fruit or juice. The tea already contributes flavor before bottling; the additions change that base. Refrigeration slows further fermentation.

For the home recipe in our brewing guide, each liter of water takes about 5 g of tea, 60 to 70 g of sugar and 100 to 200 ml of starter liquid. These are starting quantities, not a measure of the sugar or alcohol left in the drink. Commercial producers may filter, flavor, pasteurize or use other processing methods after fermentation, so their products can differ from a home batch. How to make kombucha gives the measured recipe and brewing checks.

What it tastes like

Early in fermentation, kombucha often tastes like sweet tea with a sour edge. As the culture produces more acids, the drink becomes sharper and may develop a vinegar-like aroma. The sweetness and acidity you prefer determine its taste at bottling, alongside the tea and any additions. Black tea usually gives a darker, fuller tea flavor; green tea tends to taste lighter or more grassy. Fruit juice can add sweetness after fermentation, so two equally tart bottles may still contain different amounts of sugar.

What kombucha contains

The table describes components you may find in finished kombucha and what affects them. A commercial label gives information for that product and serving size. For a home batch, tasting and counting fermentation days cannot give you a reliable sugar or alcohol measurement. Changing the tea, starter or bottling conditions can change the composition even when you follow the same recipe.

For quantities and label comparisons, read sugar, caffeine and calories in kombucha. The guide to alcohol in kombucha explains why bottling and storage matter. A live culture label also needs context: identifying microbes in a drink doesn’t show that those organisms provide a health benefit at the amount consumed. Is kombucha good for you? examines the evidence behind probiotic and other health claims.

Research has reported glucuronic acid in some kombucha preparations, but finding a compound doesn’t establish a “detox” effect from drinking it. Health benefits need evidence from human studies. Laboratory measurements of acids or antioxidant activity describe a sample; they don’t tell you how your batch will affect your health. Treat those measurements separately from claims on a bottle or in a brewing recipe.

What kombucha labels mean

• Raw or unpasteurized: no pasteurization step after fermentation. Active culture can keep fermenting and may form a small pellicle in the bottle. Keep it refrigerated. A plain bottle may supply starter culture, but the label alone doesn’t tell you how active it is.
• Pasteurized: heat-treated to reduce or inactivate the culture. Storage requirements depend on the finished product, so follow the label. Pasteurization doesn’t tell you the alcohol content or establish that every product can stay unrefrigerated.
• Hard kombucha: made as an alcoholic drink, through fermentation or added alcohol. Check the stated alcohol by volume; “hard” identifies the product category rather than a fixed strength.
• Jun: a ferment made with green tea and honey, using a culture maintained for that recipe. Its fermentation time and alcohol content depend on the culture and brewing conditions.
• Concentrates, powders and “kombucha flavored” drinks: the name alone doesn’t tell you whether the product contains fermented tea. Check the ingredients and preparation instructions, as well as any claim about live cultures.

How it compares to similar drinks

Water kefir uses grains that you retain for the next batch, while kombucha brewing uses starter liquid and often a pellicle. Milk kefir also uses a reusable culture, with milk as its base. A prebiotic soda generally contains added fibre; the word “prebiotic” describes an ingredient’s intended role, not a fermentation method. For vinegar drinks, check the processing and added ingredients rather than assuming every bottle contains the same culture or flavor.

Where kombucha comes from

Accounts of kombucha’s origins commonly place it in northeast China, followed by Japan and Russia. The BCCDC guideline repeats the often-cited Manchurian origin dated to 220 BC, drawing on a review of kombucha literature. This is a reported history, not a record that lets you trace a modern starter to a particular ancient batch. Precise dates and stories about imperial tonics need historical evidence beyond a description of the fermentation.

Home brewing continues through the transfer of starter liquid and cultures between batches, including cultures obtained from other brewers. Commercial bottles use their own recipes and processing methods. A culture’s source tells you where you obtained it, but not how many generations it has passed through. When you receive a starter, ask about its recent brewing conditions and whether it has been fermenting actively; that information is more useful for your next batch than an assumed ancient lineage.

Is it safe?

Acidity alone doesn’t confirm that a batch is safe. Proper fermentation helps inhibit some harmful microbes, but clean handling, suitable containers and storage still matter. Mold, contamination and unsuitable ceramic glazes can create problems; excessive acidity and alcohol also affect who should drink it. Use the checks in how to make kombucha before bottling, and consult kombucha mold if you find unfamiliar surface growth. A normal taste or pellicle cannot rule out every risk.

Frequently asked questions