Kombucha is sweetened tea fermented by a SCOBY – a rubbery disc that’s a “symbiotic culture of bacteria and yeast” – plus some already-fermented kombucha as starter. The yeast turns sugar into alcohol and carbon dioxide, and acetic acid bacteria turn much of that alcohol into acids, so the tea becomes tart, slightly fizzy and much less sweet over one to two weeks. Here’s how to brew it, the proportions from the recipe we first made and photographed in 2016, and what’s known about its safety and health effects.
What You Need
- A SCOBY and starter liquid: from a friend’s batch or a shop, or grown from a bottle of raw, unflavored kombucha. The starter matters as much as the SCOBY: it acidifies the new tea straight away.
- Tea: black or green tea (Camellia sinensis), or a mix. Herbal and flavored teas with oils are best kept for the second fermentation.
- Sugar: plain white or light cane sugar is easiest for the culture. Honey is used for jun, a different culture.
- A glass jar of 2–4 litres, a tightly woven cloth and a band.
Use glass for brewing. Kombucha is acidic enough to leach lead from glazed ceramics: people have been poisoned after drinking kombucha brewed in a ceramic pot (Phan et al., 1998), and a Spanish family developed lead poisoning from kombucha sold in ceramic containers (Munilla García et al., 2023). Avoid reactive metal containers too.
Timing and Temperature
- Ideal temperature: about 68–78°F (20–26°C), out of direct sunlight.
- Time: 7–14 days. Warmer is faster.
- When it’s ready: taste from day 7 with a straw slipped under the SCOBY. It should be tart with a little sweetness left. Too sweet – wait; too vinegary – it’s still usable, but bottle sooner next time. Left for weeks, it keeps going towards vinegar: see how to make vinegar at home.
What a Healthy Brew Looks Like
- A new, pale layer forming on the surface (the new SCOBY), sometimes attached to the old one.
- Brown, stringy yeast strands hanging underneath – normal.
- Bubbles trapped under the new layer, a sour-vinegary smell.
- Not normal: dry, fuzzy spots that are blue, green, black or white and raised – that’s mold. Throw out the whole batch, SCOBY included.
Second Fermentation (Flavor and Fizz)
After the first fermentation you can drink kombucha as it is, or bottle it with fruit, juice or ginger and seal it for a few more days to build fizz. See our kombucha second fermentation guide for 20 flavors and amounts.
Alcohol
All kombucha contains some alcohol. In the US, kombucha that reaches 0.5% alcohol at any point is regulated as an alcoholic beverage (TTB); the kombucha used in one clinical trial measured 1.5% (Mendelson et al., 2023). Homemade kombucha, especially after a second fermentation, can be stronger than you’d expect – keep that in mind for children, during pregnancy, and for anyone avoiding alcohol.
What the Evidence Says About Health
Kombucha is often marketed with long lists of benefits, but human evidence is thin. A 2019 systematic review of 310 articles found only one study reporting results in human subjects (Kapp and Sumner, 2019). Since then, a small pilot trial in 12 adults with type 2 diabetes found lower fasting blood glucose after 4 weeks of daily kombucha, with no significant change on placebo; the drinks were donated by a kombucha maker, and the authors called for larger studies (Mendelson et al., 2023). Kombucha contains live yeasts and acetic and lactic acid bacteria, but claims about detoxification, cancer, arthritis or immunity aren’t supported by human research.
Who Should Be Careful
In 1995, two people in Iowa became severely ill (one died) after drinking kombucha from the same culture; the cause wasn’t established, but the CDC advised caution (CDC, 1995). Case reports have also linked kombucha with serious lactic acidosis, including in a man newly diagnosed with HIV (Kole et al., 2009). If you’re pregnant, immunocompromised, or have kidney or liver disease, check with your doctor first. For everyone else, start with a small glass and keep home brewing clean: glass jars, clean hands and utensils, and a properly acidic starter.
More: how long kombucha lasts, kombucha vs water kefir and how much fermented food per day.
