Fault
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.
Also called fobbing, foaming over.
Gushing is sometimes only messy and sometimes the first sign that a bottle is dangerously over-pressurised, and there is no way to tell which from the outside. Treat a gushing batch as pressurised until shown otherwise. Warning signs that the pressure route is involved: a plastic control bottle from the same batch gone hard, crown caps domed upward, corks pushing out, bottles that were meant to be still, or any bottle from the batch having already burst. Safe handling: chill the bottles thoroughly first, which both lowers the pressure and reduces the violence of the release; do not shake or invert them; carry them in a closed crate rather than by the neck; wear eye protection; and open each one behind a barrier — a cupboard door, a heavy towel, a bucket — with the neck pointed away from yourself and everyone else. Never warm a bottle to make it easier to open, never store the batch in a warm room, conservatory or car, and never put a pressurised bottle in a freezer. If a batch cannot be opened safely, chill it and dispose of the bottles unopened, wrapped, in a rigid closed container.
- Severity
- Safety — there is a real hazard here
- Where it starts
- Carbonation, Storage, Harvest, Packaging
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Carbonation, Packaging, Storage
- Signs
- 5 recorded
What it is
Gushing is the sudden, uncontrolled release of foam when a bottle is opened. It has two quite different causes that need separating, because one is a pressure problem and one is a nucleation problem. Either the bottle contains more gas than it should, in which case gushing is a symptom of over-carbonation and the bottle is a hazard; or the gas content is normal but something in the cider — particles, protein, or material from mould-affected fruit — provides sites at which bubbles form explosively. The first requires safe handling; the second requires a look at the fruit and the process.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
How the batch behaves
- Cider erupting from the neck as soon as the closure is released
- Bottles from the same batch behaving inconsistently, some gushing and some not — Inconsistency points towards nucleation rather than pressure, since pressure is fairly uniform across a batch.
To hear
- A loud report and immediate overflow rather than a controlled hiss
To look at
- Visible particles, haze or sediment in the bottle
In the mouth
- A plastic control bottle that is hard, indicating the pressure route rather than the nucleation route
When it appears. On opening, which is the only moment it can be observed. Everything diagnostic about it therefore has to come from what else the bottle shows and from the batch record.
Chilling before opening is both the safety measure and the diagnostic test: a bottle that still gushes cold has a genuine problem, and one that does not was simply warm.
Peter Mitchell / Cider and Perry Academy
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.
- Bottle over-carbonation — Whether other bottles in the batch also gush. A whole batch gushing points at the carbonation figure; one bottle in twenty points at a microbial or nucleation cause.
- Unwanted refermentation — Look for sediment that should not be there and for a bottle that is cloudier than its neighbours.
- A warm bottle opened without chilling — Chill an identical bottle to 4 °C and open it. Most apparent gushing at room temperature is ordinary carbonation behaving as physics requires.
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 dissolved in cider is metastable once the bottle is opened: the liquid is supersaturated at atmospheric pressure and the gas must come out. How violently it comes out depends on how easily bubbles can form. Homogeneous nucleation in a clean liquid is difficult, so gas leaves slowly. Heterogeneous nucleation on particles, rough surfaces or gas pockets is easy, and the more nucleation sites there are, the faster the gas escapes.
The pressure route is simply a matter of quantity. A bottle carrying more dissolved gas than it should has more to release, and the release is correspondingly more energetic. Here gushing is a symptom of over-carbonation or unwanted refermentation, and the important consequence is not the mess but the fact that the bottle has been under pressure it may not be rated for.
The nucleation route is more interesting. In brewing, gushing is well established as being caused by hydrophobin proteins produced by Fusarium and related moulds on grain, which stabilise microscopic gas nuclei. In cider the analogous risk comes from fruit affected by rot and mould — Penicillium expansum, Botrytis cinerea and Monilinia fructigena — and from particulate material, yeast, calcium oxalate crystals and colloidal haze providing nucleation sites.
Temperature amplifies both routes. Warm cider holds less gas in solution, so the same bottle warm has more gas in the headspace and a stronger driving force out of solution. Physical agitation adds gas pockets and does the same, which is why a shaken bottle gushes and a rested one may not.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Over-carbonation from over-priming or unmeasured residual sugar | Carbonation | common |
| Refermentation in bottle raising the gas content beyond what was intended | Storage | common |
| Bottles served warm rather than chilled | Storage | common |
| Bottles moved or shaken shortly before opening | Storage | common |
| Rot and mould in the fruit contributing nucleating material to the juice | Harvest | occasional |
| Heavy haze, protein or particulate matter in an unfiltered cider | Packaging | 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 |
|---|---|---|
| Chill the bottle thoroughly and let it stand still before opening | Reliable | For a normally carbonated cider that gushes because it is warm or has been moved, this is the whole answer. |
| Open the bottle slowly, releasing pressure in stages | Partial | Easing a crown cap or holding a cork and letting gas escape gradually reduces the eruption. Do it behind a barrier with eye protection if there is any chance the bottle is over-pressurised. |
| Reduce the gas content of the batch | Partial | Where over-carbonation is the cause, the batch has to be dealt with as a pressure problem: chilled, vented or decanted and rebottled. See the over-carbonation record. |
| Filter or fine before bottling next time | Partial | Reduces the particulate route, at some cost to the character of an unfiltered cider. A choice rather than an obligation. |
| Remove the nucleating material from bottled cider | Not possible | Nothing can be done to a sealed bottle. Where mould-affected fruit is the cause, the correction is at the sorting table next season. |
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
- Get the carbonation right at source: measure final gravity, weigh priming sugar and use bottles rated for pressure.
- Sort rot and mould out of the fruit, which addresses the nucleation route and the patulin question at the same time.
- Let bottles stand undisturbed and chill them thoroughly before opening.
- Where a cider is to be sparkling and clear, allow proper settling or filtration so there is less particulate material to nucleate on.
- Store bottles upright and cool so that sediment stays compacted at the base.
The useful discipline with gushing is to work out which of the two mechanisms is in play before doing anything else, because the responses diverge completely. If the plastic control bottle is hard and every bottle gushes, this is a pressure problem and the batch needs to be handled as a hazard. If the pressure is normal and only some bottles gush, this is nucleation and the question is what is in the cider.
The nucleation side is the one people rarely consider. Brewing science has established the mould-protein route in grain thoroughly, and the parallel for cider is fruit that came in with rot on it. That makes gushing one more reason to sort fruit properly, alongside the far more important patulin question.
Serving practice accounts for a great deal of everyday gushing that is not a fault at all. A bottle-conditioned cider carried home, stood on a warm worktop and opened within the hour will foam over regardless of how carefully it was made. Chilled and left to stand, the same bottle behaves.
Where a maker has bottled a genuinely sparkling cider, some vigour on opening is expected and correct. The point at which it stops being vigour and becomes a signal is when the bottle empties itself, when caps are visibly domed, or when a control bottle says the pressure is higher than it should be.
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.
Beta-glucan
The bacterial exopolysaccharide behind ropiness, which turns a cider oily and thread-like without changing how it smells or tastes.
Calcium pectate
The gel formed when calcium bridges de-esterified pectin chains, which floats to the surface as the brown cap of a keeve and carries the juice’s nutrients out with it.
Total phenolics
The single number used to summarise everything phenolic in a juice, useful for comparing fruit and misleading whenever it is used to predict how a cider will taste.
The organisms involved
Penicillium expansum
The blue mould of stored apples and the principal producer of patulin, the one genuine chemical safety issue that rotten cider fruit raises.
Botrytis cinerea
Grey mould: a broad-host-range fruit rot whose laccase enzyme oxidises phenolics and whose glucans make a juice difficult to clarify.
Monilinia fructigena
The brown rot of apples and pears, recognisable by concentric rings of buff pustules, and a major cause of fruit loss between the orchard and the mill.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
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.
Fruit sorting
Taking rotten, mouldy and damaged fruit and foreign material out of the crop before it reaches the mill, which is the primary control on patulin in cider.
Filtration
Passing cider through a porous medium to reach a stated visual brightness, at a real cost in colloidal material, body and aroma.
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.
Cold chain
Keeping an unpasteurised, unfiltered or back-sweetened cider refrigerated from the packaging hall to the point of sale, because refrigeration is the only thing holding it stable.
Faults it is confused with
These present similarly. What separates them is set out on each page.
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.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Mould taint
Musty, earthy, cellar-damp or rotten-fruit character carried in from mouldy fruit or from mouldy equipment, and a marker that the patulin question needs asking.
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.
Protein haze
A fine haze that forms as protein and tannin combine into insoluble complexes, often appearing in a cider that had already been clear.
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 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.
- 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 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.
- 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.
- Does cider need to be refrigerated — Unopened, no — cool and dark is enough for most cider. Unpasteurised, unfiltered cider keeps far better cold, and anything opened should go in the fridge.
- How is sparkling cider made
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.
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 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.
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.