The Kombucha Carbonation Guide

Kombucha Basics: Carbonation · Watch on YouTube

How carbonation actually works

In a sealed bottle, yeast eats the sugar from your flavorings and exhales carbon dioxide. With nowhere to go, that CO₂ dissolves into the liquid — think of bottle-conditioning champagne. Carbonation only really happens in a closed container: some brewers get a little fizz in their cloth-covered F1 vessels, but real bubbles come from second fermentation in an airtight bottle. Everything on this page serves one of two goals: give the yeast accessible sugar, and keep the gas trapped.

What does "good carbonation" even mean? To Ange: a nice, bubbly mouthfeel that doesn't go flat fast, visible bubbles in the bottle and the glass, and a drink you can open straight from the fridge — perfectly bubbly, never spilling over, no mess, no wasted kombucha. Your preferences may differ, and some people want no fizz at all — that's fine too (you don't need F2 to drink kombucha). But if you want bubbles, read on.

The levers, in order

1. Stir your vessel before bottling

   Yeast settles at the bottom during F1. Stir well to redistribute it so every bottle gets its share of the workforce — this is why brewers see wild fizz variance between bottles of the same batch: the top-of-vessel bottles got too little yeast, the bottom ones too much.

2. Feed the yeast something it can reach

   Pureed or juiced fresh fruit beats chopped chunks every time — with chunks, the yeast can't access the sugar, and no sugar means no CO₂. Store-bought juice acting up? It may be pasteurized or carry yeast-inhibiting ingredients. Pineapple is a legendary fizz-builder if you want to supercharge a batch. Flavoring tips →

3. Use bottles built for pressure

   Food-grade, pressure-rated bottles with caps that seal completely airtight. A loose cap quietly leaks CO₂ all week and you'll never know why the batch came out flat. Flip-top bottles are a good bet. The full bottle & cap guide →

4. Dry your caps and bottle tops, then grip

   A quick wipe before sealing keeps liquid and fruit particles from lodging between bottle and cap. Then snug screw-caps down with a basic rubber gripper — tighter than hands alone can manage.

5. Leave them alone at room temperature — but not too long

   Ange's F2 averages ~3 days at room temperature; yours may differ and will drift with the seasons. Flat-top caps that dome slightly are telling you it's working. Once you know your timeline, stick to it — waiting too long means geysers, not more fizz.

6. Chill completely, then open

   Cold liquid holds carbonation; warm liquid throws it out of solution the instant you crack the cap. Testing fizz on a room-temperature bottle will always mislead you.

Two levers people forget: the yeast itself

• Don't "clean" the brown stringy bits off your SCOBY. That unappetizing, mucus-y-looking growth is the very yeast that builds your carbonation. Unless the SCOBY is completely covered, leave it alone — chronic flat batches sometimes trace back to over-enthusiastic yeast removal.
• Take care of your SCOBY. A healthy SCOBY produces fizzy kombucha. Fizz problems? Think back through the SCOBY-care rules: did flavorings touch it? Was it refrigerated or left somewhere cold? Was it bought from a shady source? A weak culture or an off yeast-bacteria balance can be the real culprit — in which case the fix is a fresh SCOBY with strong starter tea.

Fizz without flavoring? Sure.

You don't need fruit to carbonate. Bottle plain kombucha straight after F1, seal airtight, rest a few days at room temperature, chill and test. If it stays flat or takes too long, the yeast probably needed more food — add a teaspoon of sugar per 16-oz bottle and run F2 again.

About the raisins and eggshells…

Two folk tips make the rounds. Raisins: the theory is their sugar feeds the yeast without changing flavor — but by that logic, just use more of your actual flavoring or add a teaspoon of sugar; Ange hasn't found the raisin method any more effective. Crushed eggshells: she's never needed to resort to it, and cracking eggs just for fizz isn't her favorite idea. That said — everyone's variables differ, and if either works for you when nothing else has, no knocking it. Do what you've gotta do for your bucha.

Why Ange doesn't burp her bottles

First, the definition: "burping" is opening your bottles ever so slightly during second fermentation to release "excess pressure" — many brewers recommend doing it daily or every other day. Does Ange recommend it? No. It's a controversial stance with homebrewers, but she finds burping unnecessary and counterproductive to fermentation — in a lot of cases it actively sabotages the carbonation you're trying so hard to build. Your yeast takes you two steps forward; every burp takes you one step back.

Warm temperatures greatly exaggerate carbonation — and that misleads burpers. Picture it: you burp a room-temperature bottle to check on it, the liquid fizzes up aggressively, maybe makes a mess. "It's really carbonated — better fridge it before it over-carbonates!" Then it chills, you open it… flat. What gives? A lot of brewers conclude that refrigeration "removes" carbonation. Whenever someone tells Ange the fridge zapped their fizz, she asks whether they burp — and almost every single time, the answer is yes. It's not the cold, it's the burping. That bottle was never over-carbonated: warm liquid just can't hold its bubbles (room temperature is basically a push-up bra for fizz — all illusion), so the burp vented most of the real CO₂, and the cold, dormant yeast couldn't rebuild it. Cold liquid holds bubbles — that's why a chilled bottle drinks fizzy instead of erupting.

Poor-quality bottles gave people unfounded fears. Glass explosions are a real and understandable fear (and some kombucha Facebook groups perpetuate it without looking for the actual cause). But explosions can happen in poor-quality bottles even if you burp — the culprit is essentially always thin glass, square bottles, decorative bottles, IKEA-grade flip-tops, or bottles never meant for pressure. Ange has had exactly one bottle break: a thin-glass beer bottle from her cheap-bottle experiments, left too long on a hot summer day — and because it sat in a closed cabinet, it was no big deal. With quality bottles, the worst she's ever had is a cap unscrewing slightly and leaking. The real precautions: the right bottles, and a closed cabinet or ice-free cooler to contain any surprises while you learn your rhythm.

Her actual routine: about 3 days of F2 at room temperature, then into the fridge. Most bottles are perfectly carbonated at that point — no burping, no mess. In the rare case a batch isn't fizzy enough, the bottles come back out for another day or so at room temperature, then chill again before re-testing. Much simpler than burping!

The one time burping is a good idea: deliberately long room-temperature ferments. If you want a dry, less-sweet kombucha, you'll leave bottles out 5, 7 or more days so the yeast can eat as much sugar as possible — and that will over-carbonate them. In that case, burp regularly to release excess pressure while the sweetness ferments down to where you like it. (Same goes for long-term aging: burp every month or two.)

Kombucha Basics: Is Burping Necessary? · Watch on YouTube

Still flat after all that?

Work the flat-kombucha checklist. And know that occasionally it really is the culture: some SCOBYs just don't carry carbonation-happy yeast. If you've pulled every lever for several batches, consider adopting a SCOBY from a brewer whose kombucha you know gets fizzy.

*Some links above are affiliate links — Ange may get a small cut of Amazon's profit at no extra cost to you. She only recommends what she's bought and tested herself.