How long does kombucha take to ferment?

Two-phase fermentation explained

Kombucha fermentation has two distinct phases, often confused. First fermentation (F1) is the SCOBY-driven conversion of sweet tea to kombucha — the actual fermentation. Second fermentation (F2) is optional, in sealed bottles, and creates carbonation through residual sugar + CO₂ pressure.

F1 (first fermentation) — sweet tea → kombucha

The SCOBY (symbiotic culture of bacteria and yeast) consumes the sucrose in sweet tea over 7–21 days. Three things happen: 1. Yeasts (*Brettanomyces*, *Zygosaccharomyces*) ferment sucrose → ethanol + CO₂ 2. Acetic acid bacteria (*Komagataeibacter xylinum* + relatives) oxidize ethanol → acetic acid 3. Lactic acid bacteria produce a smaller amount of lactic acid

The net result: pH drops from ~5.0 → 2.5–3.5, sweetness drops, sourness rises, alcohol content stays ~0.5% (legal threshold for non-alcoholic in most countries).

F1 timing benchmarks

• 5–7 days: mild, slightly sweet kombucha. Lower acidity, sugar still detectable. Probiotic content lower (LAB still ramping up).
• 10–14 days (recommended): classic kombucha tang. Balanced sour-sweet. Standard commercial profile.
• 18–25 days: vinegary, low-sugar. Sharper, more astringent. Best for: cocktail mixers, marinades.
• 30+ days: kombucha vinegar territory. Sour like apple cider vinegar. Use as salad dressing acid, brine acid, beverage shrub base.

Test-by-tasting protocol

Start sampling at day 7. Use a clean straw to pull a small amount — DO NOT contaminate the brew. Taste: - Still sweet + barely tart → keep going, retest in 2 days - Balanced sweet + tart → ready for F2 (or drink as still kombucha) - Tart-dominant + minimal sweet → at the edge; F2 may not develop fizz (not enough sugar left) - Pure vinegar → past peak; use as cooking acid

Temperature is the master variable

• 65°F / 18°C: 14–21 days. Slower, more complex flavor development.
• 70–75°F / 21–24°C (target): 7–14 days. Canonical home-brew range.
• 80°F+: 5–7 days but with risk of harsh, sharp, vinegary flavors.
• Below 60°F: fermentation stalls; SCOBY may go dormant.

Most home brewers target 70–75°F. A warm spot (top of fridge, near a vent) helps in cold homes.

F2 (second fermentation) — adding the fizz

If you want carbonation: 1. Bottle the F1 kombucha into pressure-rated bottles (Grolsch-style swing-tops or commercial brewer bottles — never thin glass; pressure builds rapidly) 2. Add a small amount of fruit, juice, or sugar (1 tablespoon per 16 oz) — this is fuel for residual yeast → CO₂ 3. Seal + leave at room temperature 1–3 days 4. "Burp" daily (open + close) to release excess pressure + check fizz 5. Refrigerate before opening to slow CO₂ + minimize geyser risk

F2 timing

• 1 day: light fizz
• 2 days: standard fizz
• 3 days: high fizz, geyser risk if not refrigerated

Cross-reference: see /pages/how-long-does/apple-cider-vinegar-ferment for related acetic-acid fermentation + /pages/how-long-does/kombucha-first-fermentation for F1 sugar math + /pages/how-long-does/yeast-bread-bulk-fermentation for thermal ranges.