Storage

Handling pressurised bottles safely

How do I know if a cider bottle is dangerously over-carbonated, and what should I do about it?

In short

A bottle that is refermenting beyond what its glass was designed for can fail, and glass failing under pressure produces fragments travelling fast enough to cause serious injury, particularly to the eyes.

The warning signs are recognisable: a crown cap that has lifted or domed, weeping or crusting around the closure, a cork pushing out of the neck, a bottle that gushes violently when opened cold and settled, and a previously still cider that has become cloudy and hard.

The response to a suspect batch is to move it cold, keep it away from people, protect yourself and open the bottles deliberately over a sink — not to leave it and hope.

Why this is a real hazard

Carbonation stores energy. A bottle at three or four atmospheres of internal pressure holds a quantity of compressed gas that, if the container fails, is released in an instant and accelerates the fragments outwards. A purpose-made sparkling bottle is thick, heavy and punted precisely to contain this; a lightweight still-cider bottle, a reused screw-top bottle or a preserving jar is not.

The pressure in a bottle is set by how much fermentable sugar was available to the yeast, and it can go far beyond what any bottle is rated for. A cider bottled before fermentation had genuinely finished, or a sweetened cider that was not stabilised, has a large sugar reserve and no upper limit on where the pressure goes.

Temperature adds to it in two ways. Warmth restarts dormant yeast, and warmth raises the pressure of the gas already present. A batch that was stable in a cold shed can become dangerous in a warm room.

Bottles usually fail when handled — picked up, knocked, or opened — which is precisely when a person is closest to them. The injury pattern is lacerations and eye injuries, and eye protection is not an over-reaction when dealing with a suspect batch.

The signs of a bottle that should not be opened casuallyA crown cap that is domed, lifted or rusting at the crimp; cider weeping or a sticky crust around the closure; a cork pushing out of the neck; a bottle that is noticeably harder or colder to the touch than its neighbours; a still cider that has become cloudy and fizzy; a plastic bottle from the same batch that has gone rigid. Any of these means treat the whole batch as suspect, not just that bottle.

How bottles become over-carbonated

Causes, and what makes each one worse
Cause	What happens	Aggravating factor
Bottled before fermentation finished	Remaining sugar ferments in the bottle with no relief	Warm storage; a cider that appeared stable because it was cold
Too much priming sugar	Pressure overshoots the intended level	Uneven mixing, so some bottles are far worse than others
Sweetened without stabilising	Added sugar plus viable yeast	Any warmth at all
Sugar-tolerant spoilage yeast	Ferments sugars a normal strain leaves alone	Long storage; contamination at bottling
Malolactic fermentation in bottle	Carbon dioxide produced from malic acid after bottling	Warm storage of a cider with high malic acid and live bacteria
Unsuitable bottles	Ordinary pressure exceeds what the glass can hold	Reused thin-walled or damaged bottles

What to do with a suspect batch

Stop moving the bottles more than you must, and do not carry them against your body.
Move them somewhere cold immediately. Cold slows or stops the fermentation and lowers the pressure of the gas already present. A refrigerator is ideal; an unheated outbuilding in winter will do.
Put them somewhere a failure would harm nobody — a closed sturdy box, a crate with a lid, or a bin — and not in a kitchen, a hallway or anywhere people pass.
Wear eye protection and heavy gloves before handling them, and use a cloth over the bottle when opening.
Open them over a sink, deliberately, one at a time, with the neck pointed away from you and from anyone else, and vent slowly rather than removing the closure in one movement.
Once vented, a bottle can be recapped loosely, or the cider can be transferred and stabilised; either way the pressure problem is resolved by releasing it under control.
If a bottle has already broken in storage, treat everything around it as contaminated with glass, and treat the remaining bottles as more suspect rather than less.

Preventing it

Bottle only when fermentation is genuinely complete, confirmed by stable gravity readings taken several days apart at a temperature warm enough for yeast to be active. A gravity reading taken once tells you nothing about whether fermentation has stopped or merely paused.

Prime by calculation rather than by habit, mix the priming solution thoroughly through the whole batch rather than dosing bottle by bottle, and fill a plastic test bottle from every batch so the pressure can be monitored without opening glass.

Use bottles rated for pressure where any carbonation is intended. Champagne-style bottles and heavy crown-cap bottles are designed for it; still-wine bottles, screw-top bottles and reused thin glass are not, and no amount of care compensates for the wrong container.

Where a cider is to be sweetened and not conditioned, it must be stabilised — by filtration, by pasteurisation, or by an appropriate combination of sorbate and sulphite — before the sugar goes anywhere near the bottle.

Also answered on this page

Questions this page covers, so you can tell at a glance whether it is the one you want.

Can cider bottles explode?
Why is my cider bottle cap bulging?
What do I do with over-carbonated bottles?

What people ask next

Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.

Why did my cider bottles explode — Because fermentable sugar was still present, or too much priming sugar was used, and the pressure exceeded what the bottle could hold. Never bottle a cider whose gravity is still falling, and never use bottles not designed for pressure.
How do i open a bottle-conditioned cider without losing half of it
How much pressure builds up in a bottle of cider — Enough to matter. Every gram of sugar fermented in a sealed bottle produces gas, and a bottle not rated for it can fail. The French cider appellations require a minimum of 1.0 to 1.5 bar at 20 °C, and a bottle-conditioned cider can go well beyond that if it was filled with more sugar than intended.
Why did my sweetened cider start fermenting again — Live yeast met the sugar that was added back. Sweetening is only stable if the yeast has been removed by sterile filtration, killed by pasteurisation, or held in check by sorbate together with sufficient sulphite.

Sources

What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.

The New Cider Maker’s Handbook: A Comprehensive Guide for Craft Producers
Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against the Open Library union catalogue: Chelsea Green Publishing, 2013, ISBN 9781603584739, one edition recorded. That establishes the citation points at a real book in a stated edition, which is what a citation needs and is all it establishes. No copy was opened and nothing is quoted from it. The book itself is in print and not digitised in any open collection; where CiderHQ needs a figure from this territory it uses an accessible research source instead and says so.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
The Science of Cidermaking and associated technical writing
Andrew Lea · reference work · passage verified 2026-08-24
Written by a food chemist who worked at Long Ashton on apple phenolics. Unusual among specialist cider writing in that it is primary-research-adjacent: the author is describing work he did, and cites the literature. This is why it is registered at tier 1 for chemistry while a general cider book is not.
Peer-reviewed literature on cider fermentation microbiology
Various journals · peer-reviewed literature · registered as competent for this subject
Covers the microbial succession of spontaneous cider fermentation, the role of non-Saccharomyces yeasts in the early stages, malolactic conversion by Oenococcus and Lactobacillus species, and the organisms behind the principal spoilage faults.