Making guide
Working safely: pressure, fruit and gas
What is actually dangerous about making cider?
In short
Three things, and they are not the three people usually worry about. Pressurised glass can injure and does so by fragmenting. Rotten fruit carries patulin, a mycotoxin that survives fermentation and is regulated in juice. Carbon dioxide from an active fermentation displaces air and is genuinely dangerous in a cellar, a tank or any enclosed space.
Home fermentation does not produce methanol at hazardous levels, does not produce botulism, and does not require any additive to be safe. The methanol fear is a distillation problem imported into a context where it does not apply, and the botulism fear is a preserving problem that an acidic, alcoholic, oxygenated liquid does not present.
The largest real risk to most home makers is a bottle. Everything else on this page is less likely to hurt you than the crate in the cupboard.
Who this is for. Anybody making cider or perry at any scale, and particularly anybody who has read alarming advice somewhere and wants to know which parts of it are real. (no experience assumed · 6 steps)
Carbon dioxide is a hobby-scale nuisance and a commercial-scale hazard: a tank room or a cellar with several fermenting vessels can accumulate a genuinely dangerous atmosphere at floor level, and confined-space procedures exist for exactly that reason. Above hobby scale, the food-safety obligations become legal ones rather than sensible ones.
The path
Each step says what happens, why it matters downstream, and what you are actually deciding. The links under a step are where the depth is.
1. Pressurised glass, which is the real one
A carbonated cider holds dissolved carbon dioxide under pressure, and the pressure rises steeply with temperature. Ordinary bottles are not designed for it. A still-wine bottle, a screw-top bottle or a plain flip-top will fail, and glass at several atmospheres fails by fragmenting rather than by cracking quietly.
The two arithmetic errors that cause it are priming a cider that has not finished fermenting, and ignoring the carbon dioxide already dissolved when calculating the priming sugar. Both produce a figure that looks reasonable and a pressure that is not.
Why it matters: This is the only hazard in cider-making with a mechanism for serious injury, and it is entirely preventable by two measurements taken beforehand.
HazardUse bottles rated for pressure — champagne bottles with crown caps or caged corks at domestic scale. Store conditioning bottles cool and in a closed crate. If a bottle bulges, weeps or gushes, chill it, do not shake or invert it, and vent it behind a barrier with eye protection and the neck pointed away from you and from anybody else.
What to measure
- A stable gravity across several days before bottling — Whether the fermentation has finished. Without it, the priming sugar is being added to an unknown quantity of remaining sugar. Work it out.
- Pressure at the warmest temperature the bottles will see — Whether the glass and closure can hold it. The cellar temperature is not the figure; the warmest week of the year is. Work it out.
What can go wrong here
Tools for this step
Go deeper
- Bottles and pressure: what glass will and will not hold — What each bottle type actually holds.
- Handling pressurised bottles safely — The handling procedure for bottles already suspect.
- Bottle over-carbonation — The mechanism and the full safety note.
- Bottle pressure management — Controlling it as a production operation.
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.
2. Rotten fruit, patulin, and why fermentation does not help
Penicillium expansum is the blue-green rot found on stored and bruised apples, and it produces patulin. Patulin is stable enough to survive pressing and fermentation, it is regulated in apple juice in most jurisdictions, and no step in cider-making removes it once it is in the juice.
The control is entirely at the fruit. Discard visibly rotten fruit, cut out rot rather than pressing round it, do not press fruit that has been lying wet on the ground for weeks, and wash fruit that has. Fermentation does reduce patulin somewhat, but the reduction is partial and is not a control measure.
Why it matters: It is the one respect in which "use up the windfalls" is bad advice, and it is a health question rather than a flavour one.
Take care hereDiscard rotten fruit rather than pressing it. Patulin is regulated in apple juice precisely because it is not removed by processing, and the limits exist because the toxin is a genuine concern rather than a theoretical one. Where fruit has lain on wet ground, washing and sorting are the controls.
What can go wrong here
Go deeper
- Patulin contamination — The full record: what it is, what the limits are, and what controls it.
- Penicillium expansum — The organism that produces it.
- Patulin control — The control measures as a production operation.
- Fruit sorting — The step that does the work.
- Windfalls and fruit on the ground — What ground fruit brings with it, good and bad.
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.
European Union; assimilated into UK law and maintained by The National Archives · legislation · passage verified 2026-08-24
Registered because it answers, in law and in a number, the question of what rotten fruit actually costs. Patulin is a mycotoxin produced by moulds — principally *Penicillium expansum* — growing on bruised and damaged apples, and it survives pressing and fermentation. Cider is not lumped in with fruit juice here: it has its own line in the table, at the same limit. That is the sharpest available answer to "does it matter if some of the fruit is rotten", and it is why windfall selection is a food-safety control rather than only a quality preference.
European Food Safety Authority scientific opinions
EFSA · regulator · retrieved 2026-08-24
Registered for the food-safety questions cider genuinely raises: patulin in juice from rotten fruit, sulphite sensitivity, and the toxicology behind additive limits.
Codex Alimentarius food standards
FAO / WHO · standards body · retrieved 2026-08-24
3. Carbon dioxide, which is heavier than air
A fermenting vessel produces carbon dioxide continuously and in quantity. It is colourless, largely odourless, heavier than air, and it collects at floor level in an unventilated space. In a domestic setting with one or two vessels this is a non-issue; in a cellar with several, or anywhere with a tank, it is not.
The specific danger is entering a vessel or a low unventilated space that has been accumulating it. Carbon dioxide displaces oxygen, and a person entering a high-concentration atmosphere loses consciousness quickly and without useful warning.
Why it matters: It is the hazard that scales fastest with production volume, and the one most likely to be underestimated by somebody who has just moved from demijohns to a tank.
HazardNever enter a fermentation vessel, and never work alone in an unventilated cellar with active fermentations. Ventilate at low level, because carbon dioxide collects at the floor. Above hobby scale, confined-space entry procedures and gas monitoring exist for this and should be followed rather than improvised.
Go deeper
- Carbon dioxide — What it does in solution and what it does in a room.
- Inert gas: carbon dioxide, nitrogen and argon — The related question of gases used deliberately.
- Farm mill and commercial plant: what changes with scale — Where the requirements change with volume.
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.
4. Cleaning chemicals, which are more hazardous than the cider
Caustic cleaners, acid cleaners and peracetic acid are all used in cider-making and all of them are more immediately dangerous than anything in the vessel. Caustic burns, acid burns, and mixing cleaning chemicals produces gases that are hazardous in exactly the confined spaces where cleaning happens.
The practical rules are ordinary: eye protection, gloves, never mix products, never decant into an unlabelled container, and add chemical to water rather than water to chemical.
Why it matters: More cider-making injuries come from the cleaning cupboard than from the fermentation, and the risk rises with scale as the products get stronger.
Take care hereNever mix cleaning chemicals. Caustic and acid products react; chlorine-based products and acids produce chlorine gas. Use eye protection, keep products in their labelled containers, and follow the supplier’s dilution rather than a remembered ratio.
Go deeper
- Caustic and acid cleaning — What each does, and what it is for.
- Peracetic acid and other sanitisers — The common no-rinse sanitiser, and its handling.
- Sanitation — The operation itself, and where it matters most.
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.
5. The three fears that are not real
Methanol. Fermenting apple juice produces a small quantity of methanol from the demethylation of pectin, and the quantity is far below anything of concern in the finished cider. The methanol danger belongs to distillation, where a fraction can be concentrated; it does not transfer to fermentation, and nothing you do to a cider concentrates it. Freeze concentration is the one practice where the question is legitimately asked, and the answer there is that the enrichment is proportional and small.
Botulism. Clostridium botulinum does not grow in an acidic, alcoholic, oxygen-exposed liquid. Cider is well below the pH at which it is a hazard, and the fear is imported from low-acid canning, where it is entirely real. Bottled cider is not a low-acid canned food.
Wild yeast. A spontaneous fermentation carries a real risk of spoilage — volatile acidity, mousiness, film yeast — and no meaningful risk of poisoning. What can grow in cider makes it unpleasant rather than unsafe, with the patulin question above being about the fruit rather than the ferment.
Why it matters: Each of these fears displaces attention from the pressure question, which is the one that actually injures people.
Go deeper
- Methanol — Where it comes from in cider, and at what level.
- Clostridium species — What these organisms need, and why cider does not provide it.
- Ice concentration — The one practice where the concentration question is worth asking.
- Wild vs cultured fermentation — The real risks of a spontaneous ferment, which are sensory.
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 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.
European Food Safety Authority scientific opinions
EFSA · regulator · retrieved 2026-08-24
Registered for the food-safety questions cider genuinely raises: patulin in juice from rotten fruit, sulphite sensitivity, and the toxicology behind additive limits.
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.
6. And the product itself
Cider is an alcoholic drink. The World Health Organization’s position, which this site follows, is that no level of alcohol consumption is safe for health, and the International Agency for Research on Cancer classifies alcoholic beverages as a Group 1 carcinogen. Nothing about a cider being traditional, unfiltered, low-intervention or made from good fruit changes that.
A home-made cider’s strength is frequently higher than a commercial one and is unknown unless it was measured. A batch fermented from a high-gravity juice can reach 8% ABV or more without tasting like it, and the unit arithmetic is worth doing rather than estimating.
Why it matters: A maker is the person most likely to be drinking an unlabelled product of unknown strength, which is the one circumstance in which the arithmetic is not automatic.
What to measure
- Alcohol by volume from starting and finishing gravity — The strength. There is no other way to know it for a home batch. Work it out.
- Units per serving at that strength — What it amounts to in the measure used by drinking guidelines. UK units and the US standard drink are different quantities and advice written for one does not transfer. Work it out.
Tools for this step
Go deeper
- How strong cider is — The range, and why it is so wide.
- Alcohol units — The arithmetic, in both the UK and US measures.
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.
World Health Organization · health authority · passage verified 2026-08-24
The basis for CiderHQ publishing no health benefits for alcohol. Note carefully what this page does and does not carry: it states that no form of alcohol consumption is risk-free and that alcohol is an established carcinogen, but it does not itself set out the IARC classification. That is cited to IARC directly — see `iarc-alcohol-monograph`. The distinction matters because CiderHQ’s own rule is that a source is cited for what it actually says.
International Agency for Research on Cancer, World Health Organization · health authority · passage verified 2026-08-24 · covers Volume 100E, published 2012
Registered separately from the WHO fact sheet because the Group 1 classification is IARC’s and lives in the Monographs rather than on the fact sheet. Several pages here previously attributed it to the fact sheet, which does not carry it. IARC is part of WHO, so the claim was never wrong — it was cited to the wrong document, which is precisely the failure this evidence model exists to catch. The volume was opened on 2026-08-24 and the agent name confirmed: IARC classifies *consumption of alcoholic beverages*, not “alcohol” as a chemical. The distinction is not pedantry — it is the difference between a statement about a behaviour and a statement about a molecule.
NHS · health authority · passage verified 2026-08-24
The definition CiderHQ’s units calculator implements, read against the page rather than assumed: one UK unit is 10 ml or 8 g of pure ethanol, and units are ABV multiplied by volume in millilitres divided by a thousand — which is exactly the arithmetic in `engine/calculators.ts`.
Where to go next
Guides that follow on from this one.
Questions this answers
Shown so you can tell whether this is the guide you wanted.
- Is making cider at home dangerous?
- Can home-made cider contain methanol?
- Can you get botulism from cider?
- Why do cider bottles explode?
- Is it safe to use windfall apples?
- Is wild fermentation safe?
Where to go next
- All guides — The other paths, grouped by what you are trying to do.
- Tools and calculators — The arithmetic each step refers to, with the formula shown.
- Troubleshooting — The fault records behind every "watch for" above.
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.
European Union; assimilated into UK law and maintained by The National Archives · legislation · passage verified 2026-08-24
Registered because it answers, in law and in a number, the question of what rotten fruit actually costs. Patulin is a mycotoxin produced by moulds — principally *Penicillium expansum* — growing on bruised and damaged apples, and it survives pressing and fermentation. Cider is not lumped in with fruit juice here: it has its own line in the table, at the same limit. That is the sharpest available answer to "does it matter if some of the fruit is rotten", and it is why windfall selection is a food-safety control rather than only a quality preference.
European Food Safety Authority scientific opinions
EFSA · regulator · retrieved 2026-08-24
Registered for the food-safety questions cider genuinely raises: patulin in juice from rotten fruit, sulphite sensitivity, and the toxicology behind additive limits.
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.