Knowledge Base

Kombucha

Cultured beverage · Traditional · peer-reviewed

Sweet tea fermented by a floating mat of bacteria and yeast — the SCOBY — into a tart, lightly fizzy drink whose safety comes from its own acidity.

Moderate to make
7–14 days ferment
live-cultures, organic-acids, antioxidants supplied

Ingredients

  • Water1 L
  • Black or green tea8 g
  • White sugar70 g
  • SCOBY + mature starter kombucha150 ml

How to make it

  1. Step 1

    Brew tea, dissolve the sugar, and cool to room temperature (hot liquid kills the culture).

  2. Step 2

    Add the SCOBY and at least 10% mature starter liquid — the starter's acidity protects the batch early on.

  3. Step 3

    Cover with tight-woven cloth so it breathes but excludes insects.

  4. Step 4

    Ferment 7–14 days at 20–28 °C, out of direct sun.

  5. Step 5

    Taste from day 7. Ready when tart with only faint sweetness.

  6. Step 6

    Bottle (optionally with fruit for fizz), refrigerate, and reserve SCOBY + liquid for the next brew.

What it is

Kombucha is sweetened tea fermented by a symbiotic community of bacteria and yeast — the culture known as a SCOBY (Symbiotic Culture Of Bacteria and Yeast), the rubbery pellicle that floats on top. Over one to two weeks it turns sweet tea into a tart, lightly effervescent, mildly acidic drink.

The science

The ferment is a two-organism partnership. Yeasts (e.g. Zygosaccharomyces, Brettanomyces) invert the sucrose and ferment the sugars to ethanol and CO₂. Acetic-acid bacteria (chiefly Komagataeibacter / Gluconacetobacter and Acetobacter) then oxidise that ethanol to acetic and gluconic acids, which give kombucha its sourness and drive the pH down; the same bacteria weave the cellulose pellicle (Villarreal-Soto et al., 2018). The result is a shifting mix of organic acids, trace ethanol and CO₂ (Jayabalan et al., 2014).

Safety

Kombucha's safety is built on acidity. Always pitch at least 10% mature, acidic starter liquid so the pH starts below ~4.2 and pathogens can't establish before the culture takes over. Ferment in glass or food-grade plastic, never reactive metal (the acids leach it). Discard a batch with fuzzy, coloured mould on the pellicle. Home kombucha contains a small amount of alcohol (typically under 1%).

Signs it worked / troubleshooting

  • ✅ Good: a new pale pellicle forms, liquid clears and sours, faintly vinegary aroma.
  • ⚠️ Brown stringy strands = normal yeast, not mould.
  • 🚫 Dry, fuzzy blue/green/black spots on top = mould → discard the SCOBY and liquid, start fresh.

How to store

Bottled and refrigerated, kombucha keeps for weeks. Store spare SCOBYs in a jar of mature kombucha (a "SCOBY hotel") between brews.

References

  • Villarreal-Soto SA, Beaufort S, Bouajila J, Souchard JP, Taillandier P (2018). Understanding Kombucha Tea Fermentation: A Review. Journal of Food Science 83(3):580–588. doi:10.1111/1750-3841.14068
  • Jayabalan R, Malbaša RV, Lončar ES, Vitas JS, Sathishkumar M (2014). A Review on Kombucha Tea — Microbiology, Composition, Fermentation, Beneficial Effects, Toxicity, and Tea Fungus. Comprehensive Reviews in Food Science and Food Safety 13(4):538–550. doi:10.1111/1541-4337.12073

Related

TibicosMilk Kefir