Plain kombucha out of the brewing vessel is a flat, vinegar-tinged tea. Second fermentation is where it becomes a drink: carbonated, flavoured, bottled, ready to pour. For cocktail bars, F2 kombucha is the most-versatile in-house ferment because it carries flavour, carries colour, and reads as non-alcoholic without compromising the structure of a drink.
What second fermentation is
Kombucha brewing has two stages. First fermentation (F1) is what happens in the open vessel with the SCOBY: sweet tea becomes acidic, the SCOBY produces ethanol and acetic acid, the tea becomes kombucha. Trace alcohol (typically 0.5-1.5% ABV) is present.
Second fermentation (F2) is sealed-bottle fermentation. You move the F1 kombucha into sealed bottles with added sugar or fruit, the residual yeast eats the sugar in the closed environment, and CO2 builds up. Carbonation. The bottle pressure also reactivates flavour compounds.
F2 typically takes 1-3 days at room temperature, then refrigerated to slow further fermentation.
The bottle question
Use thick-walled glass: GROLSCH-style flip-top bottles (the most popular for home F2), 33cl or 50cl, the rubber gasket ensures a tight seal. Or champagne-style bottles with cork closures.
Do not use regular wine bottles, jam jars, or thin-walled glass. They will explode under pressure. Plastic PET soda bottles are safer (they bulge before breaking) but discolour and absorb flavours over reuse.
"Burp" your bottles every 12 hours during active F2. Slightly crack the seal, hear the gas hiss out, reseal. This prevents over-carbonation and explosions.
Flavour additions that work
Fresh fruit: add 50-100g per litre. Strawberry, blueberry, raspberry, mango, pineapple. Citrus zest works (no pith). Whole or muddled.
Herbs and spices: 2-3g per litre. Ginger (the classic), turmeric, mint, basil, lemongrass, kaffir lime leaf, pandan.
Tea infusions: brew a strong tea (e.g. jasmine, Earl Grey, chamomile), add 50ml per litre of F2 kombucha.
Juice: fresh pressed (not from concentrate), 50-100ml per litre. Adds sugar that feeds the second fermentation; reduce any added syrup proportionally.
Sugar source: if using only herbs or zest (no fruit), add 1-2 teaspoons of sugar per litre to feed the F2.
Our four working flavours
1. Pandan-Calamansi. 2g pandan leaf (knotted), zest of 4 calamansi, 1 teaspoon sugar per litre. Bright, Malaysian, drinks like a craft tonic.
2. Bunga Telang-Lime. 2g butterfly pea flowers, zest of 2 limes, 1 teaspoon sugar per litre. Deep blue, slightly herbal, instagram-friendly.
3. Ginger-Hibiscus. 5g fresh ginger sliced, 3g dried hibiscus, 1 teaspoon sugar per litre. Tart, rooty, dark red.
4. Mango-Cili Padi. 80g mango chopped, 1 cili padi seeded and split, no added sugar. Sweet-spicy, hits like a Southeast Asian tropical drink.
Using F2 kombucha in cocktails
F2 kombucha replaces "tonic water" or "soda" in any cocktail format, with added flavour and slight acidity.
Kombucha G&T: 50ml gin, 100ml F2 kombucha, large ice cube, garnish. The kombucha's natural acidity removes the need for added citrus.
Kombucha Highball: 45ml aged rum or whisky, 90ml F2 kombucha, ice. Works particularly well with the ginger-hibiscus or mango-cili padi flavours.
Kombucha Spritz (NA): just F2 kombucha over ice in a wine glass with a herbal garnish. The closest a non-alcoholic drink gets to "proper drink" status.
Safety notes
Brew in a clean environment. SCOBY contamination (mould) presents as fuzzy growth on top, not the slimy SCOBY layer. If you see fuzz, discard the entire batch.
Alcohol content of F2 kombucha typically reaches 1.0-2.5% ABV. Legally it can still be sold as a "non-alcoholic" beverage in Malaysia (under 1% ABV threshold). For a true zero-alcohol output, use a low-alcohol Symbiotic Yeast and freeze-distillation post-F2; for casual bar use, the trace alcohol is negligible.
Related reading
Frequently asked questions
What is second fermentation in kombucha?
Kombucha brewing has two stages. First fermentation (F1) happens in the open vessel with the SCOBY, turning sweet tea into acidic kombucha with trace alcohol. Second fermentation (F2) is sealed-bottle fermentation: you move F1 kombucha into sealed bottles with added sugar or fruit, residual yeast eats the sugar, and CO2 builds up. F2 takes 1 to 3 days at room temperature, then refrigerates to slow further activity.
How do I second-ferment kombucha at home without bottles exploding?
Use thick-walled glass: Grolsch-style flip-top bottles (33cl or 50cl) with a tight rubber gasket, or champagne bottles with cork closures. Never use regular wine bottles, jam jars, or thin-walled glass. Burp the bottles every 12 hours during active F2: crack the seal, hear the gas hiss out, reseal. This prevents over-carbonation. Refrigerate when carbonation is at target.
Which flavours work best in F2 kombucha?
Fresh fruit (50 to 100g per litre): strawberry, blueberry, mango, pineapple, citrus zest. Herbs and spices (2 to 3g per litre): ginger, turmeric, mint, lemongrass, pandan, kaffir lime leaf. Strong tea infusions (50ml per litre): jasmine, Earl Grey, chamomile. Our four house flavours are Pandan-Calamansi, Bunga Telang-Lime, Ginger-Hibiscus, and Mango-Cili Padi.
Can I substitute F2 kombucha for tonic water in a Gin & Tonic?
Yes, and the result is meaningfully more interesting. F2 kombucha brings carbonation, flavour, and natural acidity in one ingredient, so you can skip the added lime. Pour 50ml gin over a large ice cube and top with 100ml of F2 kombucha (Pandan-Calamansi or Ginger-Hibiscus both work). The kombucha's native acidity removes the need for citrus, and the flavour gives the drink a distinctive character.
Where can I try house kombucha cocktails in PJ?
Both Dissolved Solids (43-1 Jalan SS20/11 Damansara Kim) and Soluble Solids (50-1 Jalan SS2/24) run rotating F2 kombuchas as cocktail mixers and standalone NA pours. Ask the bartender for the current flavour and a pairing. The Mango-Cili Padi is the most polarising; the Pandan-Calamansi is the most ordered. Message Dissolved Solids on WhatsApp +60 11-4008 7607 or Soluble Solids on +60 11-1682 8651.