Short answer: for second fermentation, use thick, food-grade glass bottles with caps that seal airtight. Swing-top (flip-top) bottles are the most reliable choice, and recycled commercial kombucha bottles with their original caps also work. Avoid decorative or thin glass, and don’t use mason jars. Plastic isn’t a good container for the brew itself, but one clear plastic bottle makes a useful carbonation gauge.
Why bottle choice matters
Second fermentation traps carbon dioxide in a sealed bottle, which is what gives kombucha its fizz. Pressure builds as it does. A bottle that doesn’t seal loses its fizz. A bottle that can’t handle the pressure can break, and glass breaking under pressure is dangerous, so bottle choice is a safety decision as well as a quality one.
What to look for
- Thick, food-grade glass that can handle pressure.
- A cap that seals airtight. The seal matters as much as the glass, because the seal is what keeps the carbonation in.
- A round shape. Square bottles handle pressure poorly.
Swing-top (flip-top) bottles
Swing-tops are the most common choice for home brewers. A wire bail and a rubber gasket hold a tight seal, and you can release pressure easily with a quick “burp.” The downsides are small: they cost more per bottle, and the closures can feel stiff at first, though they loosen with use. Swing-tops come with ceramic tops and in 16 oz and 32 oz (1 L) sizes. The taller 32 oz bottles take up a lot of fridge space.
Thick German-style beer bottles with swing-top closures, such as Grolsch, are a common example of this type.
Recycled commercial kombucha bottles
Bottles from brands such as GT’s Synergy, Health-Ade and Kevita work well for the second fermentation if they’re thick glass with their original caps. Keep the liner inside the cap. Don’t remove it. It’s what holds the carbonation. Seal the caps tightly, using rubber grippers if you have them. If you’ve lost a cap, replace it with the right size (see below). Soaking the labels off makes the bottles easier to clean.
Specialty bottles and F217 caps
Stout, Boston round and ring-neck bottles come in many shapes and sizes, from 8 oz up. They’re less bulky than swing-tops, and buying them in bulk from a wholesale bottle distributor is usually the cheapest option.
Their caps are often F217 caps: plain, usually black, with a thin white liner. When they’re tight, they hold carbonation well and can be reused many times. They also work as a gauge. Once the bottle is well carbonated, the cap domes slightly upward, which is a sign it’s ready to refrigerate. One brewer’s testing found no significant difference between F217 caps and the more expensive polycone caps, so F217 caps are a practical choice.
Cap sizes, from one guide:
| Bottle type | Cap size |
|---|---|
| Boston round, Health-Ade | 28/400 |
| Stout, ring-neck, GT’s Synergy, Kevita | 38/400 |
Plastic bottles
Plastic bottles, and bottles with plastic liners, aren’t a good container for the brew itself. They aren’t designed for the pressure of a carbonated, fermented drink, and they can fail.
Plastic does have one useful job. Fill one clear plastic bottle with kombucha and cap it. As the brew carbonates, the bottle becomes firm. When it’s rock-solid, the glass bottles should be carbonated too. Food52’s guide calls the plastic bottle “your guide to carbonation,” and it’s the simplest way to check pressure without opening a glass bottle.
What to avoid
- Decorative or thin glass. Decorative swing-top bottles from home stores are often thin and aren’t made for pressure.
- Some decorative flip-tops. Youbrew’s guide names IKEA flip-tops specifically. They’re made for oils or decoration, not carbonated drinks.
- Square bottles. Their shape handles pressure poorly.
- Mason jars. Two-piece canning lids don’t seal consistently, so the fizz escapes. One guide puts it simply: they work, but not well.
- Standard beer bottles. Thin-walled beer bottles with crown caps don’t handle heavy carbonation reliably. One experienced brewer had a bottle break. A cautious option is to bottle flavored kombucha with no added fizz and refrigerate it straight away.
- Bottles with bare metal tops. Food52’s guide advises against metal tops, which can react with the brew.
Keeping bottles safe while they carbonate
- Fill them nearly to the top. Fuller bottles carbonate more.
- Store them in a closed cabinet or a cooler without ice, out of direct sunlight, while they carbonate.
- Don’t overload them with sugar or fruit. Extra sugar from fruit or juice can cause high pressure and burst bottles.
- Burp when needed. If a bottle feels very pressurized, open it slowly over a sink to release some pressure.
- Check the gauge bottle. Guides range from about 1 to 4 days at room temperature before refrigerating, so use the gauge bottle to judge rather than the calendar.
- Refrigerate once carbonated. Cold slows fermentation right down.
Dark vs clear glass
Clear glass lets you see the flavor and judge the color. Dark glass, such as brown or cobalt, blocks light. Direct sunlight can affect flavor and shorten shelf life. If you keep clear bottles in a dark cabinet or a closed fridge, light exposure is minimal.
Quick comparison
| Bottle | Good for | Watch for |
|---|---|---|
| Swing-top glass | Most home brewers | Higher price per bottle; stiff closure at first |
| Recycled commercial bottles with original caps | Budget starters | Caps and liners must be intact |
| Stout or Boston round with F217 caps | Buying in bulk | Replace caps if lost |
| Clear plastic bottle | Carbonation gauge only | Not for the brew itself |
| Mason jar | Flat, still drinks only | Fizz escapes |
| Decorative glass or beer bottles | Not recommended | Breakage under pressure |
For covers during the first fermentation, see what to cover your kombucha with. For a large batch, see brewing kombucha in a 5-gallon carboy.