How to brew kombucha at home: SCOBY, first and second fermentation, safety
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Kombucha is sweetened tea fermented by a SCOBY, a symbiotic culture of bacteria and yeast that looks like a rubbery pale disc. The yeast turns the sugar into alcohol and carbon dioxide; the bacteria turn much of that alcohol into acids. The result is a sour, lightly fizzy drink. It is easy to make, but because it is acidic and sits for days at room temperature, a few safety rules are worth taking seriously.
What you need
- A SCOBY plus some mature kombucha (starter liquid) from a previous batch. Getting one from someone who brews regularly is common; buying a live culture also works.
- Tea: plain black or green tea. Avoid flavoured teas and teas with oils, which can harm the culture.
- Sugar: ordinary white sugar is the easiest for the culture to use.
- Water: tap water is usually fine; if yours is heavily chlorinated, let it stand or boil it first.
- A glass jar of a few litres, a breathable cloth cover and a rubber band.
- Bottles with tight lids if you want fizz, designed to hold pressure.
Choose your vessel carefully
Kombucha is acidic enough to pull metals out of some containers. There are documented cases of lead poisoning from kombucha brewed in a glazed ceramic pot, so:
- Use glass. Plain, uncoloured glass is the safest choice.
- Avoid ceramic unless you are certain it is lead-free and made for food, and avoid lead crystal.
- Avoid reactive metals such as aluminium. Opinions differ on stainless steel; glass avoids the question.
- Be wary of jars with metal or plastic spigots that sit in the liquid.
First fermentation
- Brew a strong tea with hot water, stir in the sugar until it dissolves, then top up with cold water.
- Let it cool to room temperature. Hot tea kills the culture.
- Pour it into the jar and add your starter liquid. A good proportion of mature kombucha matters: it acidifies the new tea straight away, which protects it in the first days.
- Lay the SCOBY on top (it may sink or float; both are fine).
- Cover with a tightly woven cloth to keep out fruit flies and dust.
- Leave it at room temperature, out of direct sunlight, for around one to two weeks.
- Start tasting after about a week by drawing liquid from below the SCOBY with a clean straw. It is ready when it has lost most of its sweetness and tastes pleasantly tart.
Keep the SCOBY and some of the brew as starter for the next batch.
Second fermentation (for fizz and flavour)
- Pour the finished kombucha into pressure-safe bottles, leaving a small gap at the top.
- Add flavouring if you like: a little fruit, juice or ginger.
- Seal and leave at room temperature for a few days. The remaining yeast makes carbon dioxide, which has nowhere to go and dissolves into the drink.
- Refrigerate once it is fizzy enough.
Pressure builds quickly, especially with fruit and warm rooms. Bottles can burst. Open one carefully to check progress, point it away from faces, and move everything to the fridge as soon as it is ready.
Safety rules
- Mould: a healthy SCOBY can look lumpy, stringy and brown in places. Mould is dry, fuzzy and coloured (green, blue, black or white and furry) and sits on top. If you see mould, throw out the whole batch, SCOBY included.
- Start acidic: always add enough starter liquid. Unacidified sweet tea at room temperature is an invitation to the wrong microbes.
- Clean hands and tools: wash everything in hot soapy water and rinse well; soap residue harms the culture.
- Alcohol: kombucha contains some alcohol, and longer or warmer second fermentations can raise it. Keep that in mind if you avoid alcohol or are serving children.
- Who should be careful: if you are pregnant, have a weakened immune system or a health condition, ask a doctor before drinking unpasteurised home-fermented drinks.
- Start small: drink a small glass at first and see how it agrees with you.
What flavours have worked for your second fermentation? Share your recipes, or ask about a SCOBY that looks odd, in the comments.