Fault
Bottle over-carbonation
More dissolved carbon dioxide in the bottle than intended or than the glass is rated for — a presentation problem at the mild end and a physical hazard at the severe one.
Also called over-primed bottles, excessive bottle pressure.
Over-pressurised glass bottles genuinely injure people, and the injuries are to eyes and hands. A bottle can fail while being carried, while sitting on a shelf, or in the hand as it is opened. Treat these signs as evidence of dangerous pressure: a crown cap domed upward, a cork or swing-top straining, a plastic control bottle gone rock hard, gushing on opening, or any bottle from the batch having already burst. Safe handling: chill the whole batch first, because cold lowers the pressure and reduces the risk; do not shake, invert or knock the bottles; carry them in a closed crate or box, never by the neck; open them one at a time with the bottle behind a barrier such as a cupboard door, a heavy towel or a bucket, pointed away from you and from anyone else; and wear eye protection. Never store a suspect batch in a warm room, an airing cupboard, a conservatory or a car, and never place a pressurised bottle in a freezer. If the batch cannot be handled safely, chill it thoroughly and dispose of the bottles unopened, wrapped and in a rigid closed container. Do not add anything to a sealed bottle, and do not attempt to reseal a bottle whose glass is chipped or cracked.
- Severity
- Safety — there is a real hazard here
- Where it starts
- Carbonation, Packaging, Storage
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Carbonation, Packaging, Storage
- Signs
- 6 recorded
What it is
Bottle over-carbonation is the condition of a bottle-conditioned or force-carbonated cider carrying more dissolved gas than was planned. In mild cases the cider simply foams excessively and its texture is wrong. In severe cases the internal pressure exceeds what the bottle was designed to hold, and the bottle can fail. Unlike unwanted refermentation, which is a microbiological accident, this is usually an arithmetic or specification error: too much priming sugar, an unmeasured residual gravity, or the wrong bottle.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
To hear
- A violent hiss and immediate foaming on opening
To look at
- Cider that pours as foam and will not settle into a glass
- A crown cap visibly domed upward, or a cork pushing out of its bottle — A domed cap is direct evidence of internal pressure and should be treated as a warning.
In the mouth
- A plastic control bottle from the same batch that has gone rigid
- A harsh, prickly, gassy mouthfeel that hides the cider’s flavour
How the batch behaves
- One or more bottles from the batch having already burst — If one has gone, the rest of the batch is at the same pressure and must be treated as hazardous.
When it appears. Weeks after bottling, and the risk rises with every degree of storage temperature. The bottles that fail are usually the ones that have been moved somewhere warmer.
The hazard is not proportional to the excess. Glass rated for pressure fails abruptly rather than progressively, so a bottle at twice its intended carbonation is not twice as risky — it is either within its rating or it is not.
Peter Mitchell / Cider and Perry Academy, Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739
What it is mistaken for, and how to tell
One observation per rival, chosen because it separates them rather than because it describes either. Several of these are not faults at all — a style feature, a normal outcome, or the fruit behaving as it does.
- Unwanted refermentation — Whether a priming addition was made. Over-carbonation is an arithmetic error against a target; refermentation had no target.
- Gushing — Gushing is a symptom that over-carbonation is one cause of. A gushing bottle with a microbial history is a different problem from one that was simply primed too high.
- A correctly carbonated sparkling cider — The pressure figure at the warmest storage temperature. A cider at two volumes in a champagne bottle is fine; the same cider at five volumes is not.
Described in full
- What is plotted
- Volumes of dissolved carbon dioxide run along the horizontal axis, from one to six. Gauge pressure in bar runs up the vertical axis. Three curves are drawn, one each for 5 °C, 12 °C and 20 °C, distinguished by dash pattern as well as by label.
- Temperature is not a small effect
- The three curves diverge sharply. Three volumes of gas exerts roughly one bar at 5 °C, about one and three-quarter bar at 12 °C, and about two and a half bar at 20 °C — the same liquid, the same bottle, more than double the pressure.
- Why carbon dioxide behaves this way
- Its solubility falls as temperature rises. Warming a sealed bottle does not create gas; it drives dissolved gas out of solution into the headspace, where it registers as pressure.
- The plain cork line
- A dashed reference marks the region beyond what an unwired straight cork in a still-wine bottle will hold. Above it a cork will creep and eventually push out, which is the least bad of the possible outcomes.
- The sparkling bottle line
- A second reference marks where a pressure-rated sparkling bottle with a wired or crown closure becomes necessary. Traditional-method cider and perry sit above this line at cellar temperature and well above it at room temperature.
- The practical safety point
- A bottle conditioned to a safe pressure in a cool cellar can be carrying twice that pressure after a day in a warm room or a car. Bottle-conditioned cider should be primed for the warmest temperature it will ever see, not the coolest.
- How the curves are calculated
- From the solubility of carbon dioxide in water at each temperature: pressure is the dissolved volume divided by the solubility, less one atmosphere for the surrounding air. The figures are close approximations, and cider is not pure water.
What is actually happening
The chemistry or microbiology behind it. Understanding the mechanism is what makes the prevention make sense rather than being a list of rules.
Carbon dioxide in a sealed bottle partitions between dissolved gas in the cider and gas in the headspace, according to Henry’s law. The dissolved concentration and the headspace pressure are linked, and both depend on temperature: as a bottle warms, gas leaves solution, headspace pressure rises, and the same bottle that was safe in a cold store becomes marginal in a warm room.
Fermentation of sugar produces a predictable quantity of gas — roughly half the mass of the sugar consumed, as carbon dioxide — which is why priming is a calculation rather than a guess. The error that produces over-carbonation is almost always in the input: sugar added by habit rather than by weight, a cider that was not actually dry when primed so the priming sugar was added on top of residual sugar, or a batch primed in bulk and bottled unevenly so some bottles received more than others.
Container rating is the other half. A champagne bottle is heavy-walled and made to hold substantial pressure. A still-wine bottle, a screw-top bottle, a swing-top bottle of unknown provenance and a reused commercial bottle are not equivalent, and the difference is not visible by eye. Glass also fails less predictably as it ages and accumulates scratches.
Temperature swings do the rest. A batch primed for a cool cellar and then stored in a kitchen may exceed its rating without any further fermentation at all, simply because the equilibrium has moved.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Too much priming sugar added at bottling | Carbonation | common |
| Priming a cider that was not fully fermented, so the residual sugar added to the calculation | Carbonation | common |
| Priming solution not mixed evenly through the batch before filling | Packaging | common |
| Bottles not rated for pressure used for a conditioned cider | Packaging | common |
| Bottles stored somewhere warm after conditioning | Storage | common |
| Force carbonation set too high, or a keg dispensed into bottles under pressure | Carbonation | occasional |
Can it be put right?
Most cider faults cannot be reversed. Where that is the answer it is given plainly — an honest 'this batch is what it is' is more useful than a procedure that will not work.
| Option | Effectiveness | What it involves |
|---|---|---|
| Decant, degas and rebottle in appropriate glass | Reliable | The proper fix where the batch is worth saving: chill, open carefully, combine into a vessel, let the excess gas leave, confirm stability, and rebottle in bottles rated for the pressure intended. |
| Dispose of the batch safely | Reliable | Where the pressure is unknown, bottles have already burst, or the glass is not rated for what is inside it, this is the correct answer. Chill first, then dispose of the bottles unopened, wrapped, in a rigid closed container. |
| Chill the whole batch thoroughly | Partial | The first action, always. Cold moves gas back into solution, lowers headspace pressure, and slows any yeast still working. It makes the bottles safer to handle but does not fix them. |
| Vent and recap the bottles | Partial | Possible for a batch that is over-carbonated but not yet refermenting: chilled, opened carefully behind a barrier with eye protection, allowed to release gas, and recapped with fresh caps. Laborious and it wastes some cider. If sugar and yeast remain, the pressure returns. |
| Reduce the pressure in a sealed bottle without opening it | Not possible | There is no way to do this. Do not attempt to cool a bottle rapidly, drill it, or otherwise interfere with a pressurised container. |
CiderHQ gives no additive dosage figures. An addition is a food-safety decision that depends on legal limits, on the juice in front of you and on what you are protecting against, and the right figure comes from your supplier’s or regulator’s own guidance rather than from a general reference.
Preventing it
- Confirm the cider is genuinely at final gravity before priming, so the calculation starts from zero rather than from an unknown.
- Weigh priming sugar rather than measuring it by spoon or by memory, and calculate for the volume actually being bottled.
- Mix the priming solution into the whole batch gently and thoroughly before filling, so every bottle receives the same amount.
- Use bottles specified for pressure — heavy champagne-style glass or purpose-made crown-cap bottles — and never screw-top or twist-off bottles for a conditioned cider.
- Fill one plastic bottle per batch as a pressure indicator and check it as conditioning proceeds.
- Store conditioned bottles cool and stable, and move them to a cold place as soon as the intended carbonation is reached.
Bottle conditioning produces carbonation from a second fermentation in the sealed bottle, and it is the operation in home production where an arithmetic slip has physical consequences rather than sensory ones. The technique is controllable rather than dangerous — a measured final gravity, weighed sugar and bottles rated for pressure are what control it — but it is the one place in cidermaking where the failure mode is glass rather than flavour.
The single most common failure is priming a cider that was not finished. The priming calculation assumes the cider contributes no sugar of its own, and if it does, the total is whatever the residual sugar was plus whatever was added. Since residual sugar is exactly the thing that was not measured, the excess is unknown, and an unknown pressure is the problem.
The bottle is not a detail. Sparkling-rated glass exists because the pressure in a conditioned drink is substantial, and reusing a bottle designed for still cider, or a twist-off bottle whose neck was never made to hold a crown, converts a manageable margin into no margin at all.
Where a batch has already produced a burst bottle, the correct assumption is that every other bottle from it is at the same pressure. That is the point to stop treating the situation as a cidermaking question and start treating it as a handling question, chilling the batch and dealing with the bottles carefully or disposing of them.
The compounds involved
Carbon dioxide
The other product of fermentation, which protects a cider from air while it is being made and, dissolved in the finished drink, changes both its texture and its perceived acidity.
Glucose
The sugar yeast takes first and the smallest of the three in apple juice, which is why the last sugar left in a slow ferment is almost never glucose.
Sucrose
The disaccharide of apple juice and the sugar most often added to it, split into glucose and fructose by the yeast’s own invertase before any of it is fermented.
Ethanol
The alcohol yeast makes from fruit sugar, which converts a perishable juice into a keepable drink and carries most of its aroma to the nose.
The organisms involved
Where in the process it arises
Bottle conditioning
Carbonating cider by letting a second fermentation finish inside the sealed bottle, so the gas is generated where it is going to stay.
Priming
Adding a measured, calculable quantity of fermentable sugar at bottling so that the fermentation which follows generates a predictable volume of carbon dioxide.
Forced carbonation
Dissolving carbon dioxide into cider under pressure to a chosen level, giving complete control of the sparkle and none of the flavour a second fermentation would contribute.
Bottling
Transferring finished cider into glass, where the dominant variable is how much oxygen the liquid picks up in the few seconds it takes to fill and close each bottle.
Bottle pressure management
Matching the pressure a carbonated cider will actually generate to glass that can contain it, taking account of temperature and of any fermentable sugar left in the bottle.
Closure selection
Choosing between cork, crown, screwcap, cage and swing-top, a decision that fixes how much oxygen reaches the cider, whether it can hold pressure, and which faults it is exposed to.
Faults it is confused with
These present similarly. What separates them is set out on each page.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Gushing
Cider that erupts from the bottle on opening, either because it is over-pressurised or because something in it is nucleating the dissolved gas violently.
Under-carbonation
A cider intended to sparkle that has little or no dissolved gas, usually because the bottle conditioning never started or the closure did not hold.
Excessive sediment
More deposit in the bottle or vessel than the presentation intends, ranging from a normal conditioning yeast layer to a loose sludge that clouds every pour.
Where this comes up in a guide
The link lands on the step where the fault arises rather than at the top of the pathway, because that is where the decision that causes it is taken.
Carbonation: where the gas comes from and what it costs
How do I carbonate cider, and how do I do it without breaking bottles?
Diagnosing a batch that has gone wrong
Something is wrong with my cider. How do I work out what?
How cider is made, start to finish
How is cider actually made?
Making perry
How do I make perry, and what is different about it?
What to measure, and what each number tells you
What should I be measuring, and what do the numbers mean?
When the fermentation is not doing what it should
My fermentation is doing something strange. What is going on?
Your first batch of cider
I have apples and no equipment. What do I actually do?
Planning a batch: fruit in, bottles out
How much fruit do I need, and how many bottles will I get?
Working safely: pressure, fruit and gas
What is actually dangerous about making cider?
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 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.
- Why does my cider gush out when i open it — Either the cider is over-carbonated, or it is warm, or nucleation sites such as yeast and haze are releasing the gas all at once. Chilling the bottle thoroughly before opening solves most cases that are not genuine over-carbonation.
- Why is my bottled cider flat — Either there was no viable yeast left to ferment the priming sugar, or the bottles are not sealing, or it is simply too cold and needs longer somewhere warmer. Two to three weeks at room temperature is the usual minimum.
- Why is there sediment in the bottom of my cider bottle — In a bottle-conditioned cider the sediment is yeast and is expected — pour carefully and leave the last centimetre. In a filtered cider it means something has grown since bottling.
- How many calories are in cider — Roughly 40 to 60 kcal per 100 ml for most ciders, so a UK pint falls somewhere around 200 to 250 kcal. Alcohol contributes about 7 kcal per gram and residual sugar about 4, so both strength and sweetness matter.
- Which yeast ferments cider — Saccharomyces cerevisiae finishes almost every cider fermentation, whether it was pitched or arrived from the press house. In a spontaneous ferment it is not the first organism present, only the one that survives the alcohol it makes.
Where to go next
- The fault finder — Describe what you can smell and see, and narrow it down from the signs.
- All faults — Grouped by where they come from and how serious they are.
- Cider science — The chemistry and microbiology these faults come out of.
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.