Bottling & carbonation
Before you change your recipe, change the rubber. A tired gasket is the most common reason a second ferment does not carbonate.
By Scooter M.·Published September 1, 2026
The short answer
Test the seal with water before you blame the recipe: fill a bottle with plain water, close it, invert it and squeeze. If air escapes past the gasket, that bottle will never carbonate. Gaskets are consumable and replaceable, and EZ Cap states its swing tops are reusable and can be replaced as needed.
A second fermentation works by trapping carbon dioxide so it dissolves into the liquid rather than escaping. Every part of that depends on the bottle being genuinely sealed. A gasket that leaks slowly does not produce a slightly flatter drink; it produces a flat one, because the gas leaves as fast as the yeast makes it and the pressure never rises enough to force any into solution.
This is why gaskets top the diagnostic list on why kombucha is not carbonating. People change their fruit, their timings and their temperature, and the problem was a two-cent piece of rubber.
| Symptom | What it means |
|---|---|
| The rubber has gone hard and glossy | Perished. It no longer deforms to fill the sealing surface. |
| Cracks or splits around the ring | Replace it. A crack is a leak path. |
| Flattened permanently on one side | Compression set. It has stopped springing back. |
| Stained and smells strongly of last batch | Cosmetic, mostly — but rubber holds odors and berries stain it. |
| Sits slightly proud of the stopper | Seated wrongly on reassembly, not necessarily worn. |
| The wire cage feels loose | Not a gasket problem. The cage has lost tension and needs bending back. |
Do this on any bottle you are not sure about, and on every bottle in a new case before you trust the batch to them.
It takes two minutes and it converts a whole class of mysterious failures into a known quantity. A bottle that fails the water test at atmospheric pressure will certainly fail at conditioning pressure.
EZ Cap states its swing tops are reusable and replaceable as needed, and takes a crown cap as well. Bormioli's hermetic closure is hand-wash for exactly this reason.
EZ Cap
The only bottle here with a published pressure rating — 100 PSI — in amber glass, which is the combination a second ferment actually asks for.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
EZ Cap
The same swing top and amber glass at quart size, which turns a gallon batch into six bottles instead of ten and roughly halves the bottling job.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
Bormioli Rocco
Italian soda-lime glass with a published height and diameter and a hermetic clamp seal — the bottle that looks like a bottle, with the dimensions to check it fits a fridge door.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
A crown cap has no reusable sealing part. It is crimped once, it seals completely, and it is discarded on opening — so there is nothing to perish, nothing to seat wrongly and nothing to age in a cupboard.
This is why EZ Cap states its swing tops "are designed to be primarily sealed with a crown cap closure for long term storage", with the swing top there so you can reclose the bottle after opening it. Its 16 oz amber bottles accept both a swing top and a 26 mm pry-off crown cap. If you are conditioning a batch you intend to leave for months, that is the closure to use.
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Ranked on the published rubric. Every row jumps to that product's full write-up below; the button goes straight to Amazon.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 | Score8.3 EZ Cap Swing Top Bottles, Amber Glass, 16 oz (Case of 12) The only bottle here with a published pressure rating — 100 PSI — in amber glass, which is the combination a second ferment actually asks for. | Second ferment, one serving at a time | 8.3out of 10 | |
| 2 | Score7.8 EZ Cap Swing Top Bottles, Amber Glass, 32 oz (Case of 12) The same swing top and amber glass at quart size, which turns a gallon batch into six bottles instead of ten and roughly halves the bottling job. | Bottling a gallon in six moves | 7.8out of 10 | |
| 3 | Score8.0 Bormioli Rocco Swing Top Bottle, 33.75 oz (1 L) Italian soda-lime glass with a published height and diameter and a hermetic clamp seal — the bottle that looks like a bottle, with the dimensions to check it fits a fridge door. | A bottle you would put on a table | 8.0out of 10 |
#1 · Second ferment, one serving at a time
The only bottle here with a published pressure rating — 100 PSI — in amber glass, which is the combination a second ferment actually asks for.
Who it is for. Anyone doing a second ferment who wants a bottle with a number behind it rather than a shape that looks strong.
Source: MoreBeer published EZ Cap product specification (capacity, pressure rating, case contents, crown cap compatibility), morebeer.com/products/ez-cap-swing-top-bottles-amber-glass-16-oz-case-12, fetched 2026-09-01
Skip it if. You want to see the color of the finished drink. Amber hides it; the clear version of the same bottle does not.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
#2 · Bottling a gallon in six moves
The same swing top and amber glass at quart size, which turns a gallon batch into six bottles instead of ten and roughly halves the bottling job.
Who it is for. An established brewer bottling a gallon a week who is tired of filling ten bottles.
Source: MoreBeer published EZ Cap 32 oz amber listing, same product line as the specified 16 oz, morebeer.com/products/ez-cap-swing-top-bottles-amber-glass-32-oz-case-12, retrieved 2026-09-01
Skip it if. You are new to second ferment. Learn what your kitchen does to carbonation in 16 oz bottles, where the consequences are smaller.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
#3 · A bottle you would put on a table
Italian soda-lime glass with a published height and diameter and a hermetic clamp seal — the bottle that looks like a bottle, with the dimensions to check it fits a fridge door.
Who it is for. Someone bottling a lightly carbonated kombucha for the table, or storing finished kombucha in the fridge rather than conditioning it on a counter.
Source: Bormioli Rocco published Swing bottle specification (capacity, 12.13 in height, 3.5 in diameter, soda-lime glass, hermetic seal, care instructions), retailer specification listings retrieved 2026-09-01
Skip it if. You are chasing hard carbonation. Without a stated pressure rating, a bottle you are deliberately building pressure inside is a bottle you are guessing about — use the rated EZ Cap instead.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
Every specification cited on this page came from one of these documents, retrieved on the date shown against the product it belongs to.
Bottles compared on published pressure ratings, closure type, glass color and size — and which bottles must never hold a second ferment.
The five causes of a flat second ferment, ranked by how often each is actually the problem — starting with the one nobody checks.
Which swing tops publish a pressure rating, which are storage bottles wearing the same shape, and how to tell them apart before you fill them.
What the second ferment is, how much sugar to add, how long it takes, and how to know when to refrigerate without opening every bottle.
Why kombucha does not need a beer-brewing sanitizing regime, what genuinely needs cleaning, and the products that damage a culture.