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Beverages ferment

Kombucha

Intermediate

Sweet tea fermented by a SCOBY into a tart, lightly fizzy drink. Follow the NCHFP method exactly.

Temperature
20–25 °C
NCHFP: room temperature 68–77 °F.
Time
7–10 days
Count day 0 from the day you start (NCHFP).
Acidity (safety control)
Starter liquid pH 4.0 or below before you begin (NCHFP)
Acidity from the start keeps mould and pathogens out. A pH test, not smell, decides.

Timeline

Kombucha timeline

  1. Stage 1: Brew & cool teastart · about 3 h

    Hands-on — Steep at 71–77 °C, cool below 35 °C

  2. Stage 2: Fermentfrom 3 h · about 9 days

    Fermenting / waiting — 20–25 °C, 7–10 days

  3. Stage 3: Bottle & refrigeratefrom 9 days · keeps about 4 weeks

    Cold storage — Use within 30 days

Ingredients

  • Black or green tea
  • Sugar
  • Water
  • A SCOBY with starter liquid at pH 4.0 or below

Equipment

  • Glass jar (not glazed ceramic or metal)
  • Cloth or coffee filter cover with a band
  • pH strips
  • Thermometer
  • Bottles that can be refrigerated

Steps

  1. Wash hands; sanitise equipment in hot water at least 77 °C (171 °F) for at least 30 seconds (NCHFP).
  2. Heat water to 71–77 °C (160–170 °F); steep the tea 2 minutes; dissolve the sugar.
  3. Cool below 35 °C (95 °F).
  4. Test the starter liquid: pH 4.0 or less to proceed. If above 4.0, discard it — don't use it.
  5. Add starter and SCOBY; cover with a cloth or coffee filter.
  6. Ferment at 20–25 °C (68–77 °F) for 7–10 days.
  7. Bottle into clean, sanitised bottles and refrigerate promptly.

Is it working?

  • New pale SCOBY layer forms on the surface
  • Tart, vinegary-fruity smell
  • Starter for next batch reads pH 4.0 or lower

Smell & texture: Tart, vinegary, slightly yeasty; brown stringy yeast strands are normal.

Signs tell you it's fermenting, not that it's safe: never rely on smell or appearance alone.

Safety, mould and discard rules

Mould or yeast?

Normal: smooth, wet, pale or beige new layers; brown stringy yeast; bubbles trapped under the SCOBY. Mould: dry, fuzzy, raised patches (white, green, blue, black) on top — discard everything.

Storage

Refrigerate in clean bottles. Airtight bottles build CO₂ pressure and can burst — open carefully and don't leave them warm.

Shelf life: NCHFP: use within 30 days, refrigerated. Drinks mixed with other ingredients: drink immediately or refrigerate up to 2 days.

The science: what's happening

A SCOBY (symbiotic culture of bacteria and yeast) — a cellulose mat plus starter liquid — ferments sweetened tea. Yeasts turn sugar into alcohol and CO₂; acetic acid bacteria turn alcohol into acetic acid, so the tea becomes sour.

Organisms

  • Acetic acid bacteria (Komagataeibacter and others)
  • Yeasts (Brettanomyces, Zygosaccharomyces and others)
  • Lactic acid bacteria in some cultures

Troubleshooting

Not getting sour
Too cold or weak starter; keep at 20–25 °C and use enough acidic starter liquid.
Too vinegary
Shorten the ferment.

A dish (not a ferment) gone wrong? Try Recipe Rescue.

Learn more

Sources

Guidance changes: check the source for current wording. Original text; figures quoted from the sources where stated.