What is kombucha?
Kombucha is sweetened tea fermented by a SCOBY, a symbiotic culture of bacteria and yeast that forms a rubbery disc on the surface. The yeasts turn sugar into alcohol and carbon dioxide, and the bacteria turn the alcohol into acetic and other organic acids. The result is a tangy, lightly fizzy drink with a little residual sugar.
A basic recipe
For each gallon (3.8 L):
- Water: about 14 cups, used to brew the tea
- Sugar: about 1 cup (200 g) of plain white sugar
- Tea: 8 bags or about 15 g of black or green tea
- Starter: about 2 cups of unflavored kombucha from a previous batch
- SCOBY: one disc
The calculator scales these amounts to your jar, by sugar and tea per liter and starter as a share of the batch.
Example
For a 1-gallon batch with 12.5% starter:
- Starter: 0.47 L (2 cups)
- Water for the sweet tea: 3.31 L
- Sugar: 176 g, a little under 1 cup
- Tea: 15 g, about 7 bags
- Bottles for the second fermentation: about 7 of 16 oz, keeping some kombucha as the next starter
Step by step
- Brew the tea in part of the water, dissolve the sugar, then add the rest of the water cold.
- Let it cool to room temperature, below 85 °F, so it does not harm the culture.
- Add the starter and the SCOBY, cover with a cloth held by a rubber band.
- Ferment 7 to 14 days at 68 to 78 °F, away from direct sunlight.
- Taste from day 7. Keep the SCOBY and some starter for the next batch.
Second fermentation
For a fizzy, flavored drink, bottle the kombucha with fruit, juice or about 1 teaspoon of sugar per 16 oz bottle, close tightly and leave at room temperature for 1 to 3 days, then refrigerate. Use bottles designed for pressure, such as swing-top bottles, and open one to check carbonation, because too much sugar or time can make bottles burst.
Safety
- Use glass, food-grade plastic or stainless steel, never ceramic with lead glazes, since kombucha is acidic.
- Discard a batch with fuzzy, dry, blue, green or black mold on the surface.
- Homemade kombucha contains some alcohol and caffeine. People who are pregnant, immunocompromised or have health problems should check with a doctor before drinking it.