Diagnosis guide
Diagnosing a batch that has gone wrong
Something is wrong with my cider. How do I work out what?
In short
Deal with pressure first if there is any sign of it, because that is the only part of this with a physical hazard. Then establish whether what you have noticed is a fault at all — several of the things that alarm people are normal, and a few are the defining features of established styles.
Then gather observations rather than reaching for a diagnosis. Most cider faults share signs with at least one other, so a single smell is rarely decisive; a smell plus a taste plus something visible is much closer to an answer, and it is what the fault finder ranks on.
Finally, accept the arithmetic of remedies. For most cider faults the compound is already formed and nothing removes it. The value of a diagnosis is usually in preventing the next batch rather than rescuing this one, and a guide that implied otherwise would waste a weekend.
Who this is for. Anybody with a batch that smells, tastes or looks wrong, at any scale. It assumes you can smell and taste the cider and observe the vessel, and nothing more. (assumes some experience · 6 steps)
Described in full
- What is plotted
- A horizontal bar for each stage of production, its length the number of the 52 recorded faults that become detectable there. A fault appears at every stage it can surface at, so the bars sum to more than 52 — the median fault is detectable at three points.
- The shape
- Maturation is highest at 30, storage next at 29, then fermentation at 23 and packaging at 22. Pressing carries 11, and the orchard and harvest stages between them carry 5.
- Why this matters for diagnosis
- Detectable is deliberately not the same as caused. Volatile acidity is caused by a headspace and is noticed months later; smoke taint is caused in the orchard and is noticed in the glass. A reader knows when they noticed something and is trying to discover when it started, so the fault finder asks the first question and the records answer the second.
- The two peaks
- Maturation and storage are the stages at which the maker is doing nothing, which is exactly why they dominate. Faults do not wait for attention; they accumulate in the periods between operations, and the vessel is unattended for most of the time a cider exists.
- Safety-severity faults
- Drawn as a hatched segment at the end of each bar. All of them sit in carbonation, packaging and storage — the pressure faults — because a bottle is the only part of this process that can injure somebody, and it does so after the work has finished.
- What the chart cannot show
- How likely each fault is. A stage with thirty faults attached is not thirty times more dangerous than one with one; it is a stage at which more distinct things can be noticed.
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. Before anything else: is there a pressure problem?
Bulging caps, weeping closures, bottles that hiss for an unusually long time, or a bottle that foams out entirely on opening. Any of these means the contents are at a pressure the container was not intended to hold, and glass under pressure fails by fragmenting.
The response is to reduce the risk before investigating the cause: chill the bottles, which lowers the pressure substantially; do not shake, invert or carry them by the neck; move them in a closed crate; and keep them out of any warm room. If a bottle must be vented, do it behind a barrier, with eye protection, pointed away from you and from anybody else.
Why it matters: It is the only failure mode described anywhere on this site that can injure somebody, and it is caused by ordinary arithmetic errors rather than by carelessness.
HazardOver-pressurised glass shatters. Chill before handling, keep bottles crated, wear eye protection if venting, and never warm a suspect bottle to make it easier to open. If a batch is bottle-conditioning and you are unsure of the priming figure, treat every bottle as suspect until one has been opened cold and behind a barrier.
What can go wrong here
Tools for this step
Go deeper
- Bottle over-carbonation — The full safety note, and what causes the pressure to run away.
- Unwanted refermentation — The commonest cause: sugar and live yeast sealed together.
- Handling pressurised bottles safely — The practical handling procedure.
- Bottle pressure — What pressure the carbonation actually reaches at a given temperature.
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. Establish whether it is a fault at all
Cloudiness, sediment, a farmyard note, a marked oxidative character, a light prickle in a cider you thought was still, and a perry that has finished sweet are all normal — characteristic, in several traditions — and all of them get reported as faults.
The question to ask is what this cider was supposed to be. The same observation is a defect in a filtered modern cider and a defining feature in a West Country farmhouse one. Where the answer is genuinely unclear, intensity is the tiebreaker: a trace that adds complexity and a level that dominates the drink are different findings.
Why it matters: Diagnosing a style feature as a fault leads to remedies that remove the character the cider was supposed to have.
What can go wrong here
Go deeper
- The difference between a fault and a style feature — Where the line falls, and what moves it.
- Fault vs style feature — The distinction as a direct comparison.
- Whether cloudy cider is a fault — The commonest false alarm, answered.
- Oxidation as fault vs oxidation as style — The same chemistry, two verdicts.
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.
BJCP Beer Style Guidelines — cider and perry categories
Beer Judge Certification Program · classification framework · retrieved 2026-08-24
Opened on 2026-08-24, and the edition matters. CiderHQ registered the 2015 cider guidelines; BJCP has since published a 2025 cider edition, and the old URL now redirects into the current guidelines index. A competition style guide is a dated framework rather than a standing definition, and citing the wrong edition of one is the same class of error as citing a superseded specification. CiderHQ treats BJCP as one competition framework among several and never as the universal cider taxonomy.
3. Gather observations across senses before naming anything
Cider faults overlap heavily. Volatile acidity and ethyl acetate arrive together often enough that smell alone will not separate them. Reduction and a sulphite excess both present as sulphur. Haze has at least five distinct causes that look identical in the glass. A diagnosis from one observation is a guess wearing a name.
What breaks the tie is corroboration across senses. Three smells agreeing is one observation made three times; a smell, a taste and something visible agreeing is three observations that could each have failed independently. Note what the vessel looks like, what the surface looks like, what it smells like cold and warm, what the structure does on the palate, and what appears only in the finish.
Why it matters: The difference between a fault ranked first on one smell and one ranked first on three senses is the difference between a hypothesis and a finding.
What you are deciding
- Whether to taste it at all. If there is any suspicion of a food-safety problem — visible mould growth on fruit that went in, or a suspected rot source — do not taste to find out.
Tools for this step
Go deeper
- What to notice, in order — The specific observations worth gathering, one at a time.
- Volatile acidity vs ethyl acetate — Two faults that arrive together and are separated by one specific tell.
- Haze vs sediment — Two observations that share a word.
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.
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. Narrow the candidates, and look for what separates them
With several observations in hand, the fault finder ranks the recorded faults by how much of what you have described each one accounts for, and shows what else each candidate would produce. That last part is the useful half: finding a predicted sign strengthens the case, and failing to find it weakens it.
Two other pieces of context narrow the field faster than any smell. Where in the process did it appear — during fermentation, during maturation, or only after bottling — and what did you do just before you noticed. A fault that appeared three days after racking has a much shorter candidate list than one that has been there since the press.
Why it matters: A ranked list always looks like an answer. What makes it one is knowing which of your own symptoms it does not explain.
Tools for this step
Go deeper
- Fault finder — The signs you observed, ranked against the faults that explain them, with what separates the leaders.
- Fermentation monitoring — The record that turns "when did it appear" into an answerable question.
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. Find out honestly whether it can be fixed
Each fault record carries its remedies with an effectiveness rating, and a large number of them are rated unlikely or not possible. That is not pessimism. Once acetic acid has been produced it does not go back; once a cider has oxidised the aldehydes are formed; once mousiness is present it is present. Blending down into a larger volume of sound cider is often the only real option and it works only if the fault is below threshold in the result.
The faults that genuinely can be fixed are mostly the ones that are still in progress rather than complete: a stuck fermentation can be restarted, a reduction character can be blown off by racking with air before it becomes a mercaptan, an under-carbonated batch can be re-primed. The window is short in each case, which is why establishing the fault quickly matters more than establishing it precisely.
Why it matters: A maker who knows the batch cannot be recovered can spend the effort on the next one instead, which is where it will actually change something.
What can go wrong here
Go deeper
- Restarting a stuck fermentation — The one common fault with a reliable remedy, and its conditions.
- Reduction — A fault with a short window in which it is reversible.
- Volatile acidity — A fault with none, and what blending down can and cannot do.
- Blending — Dilution below threshold, which is the general fallback.
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.
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.
6. Work out what to change, and write it down
Every fault record carries a prevention list, and the prevention is almost always cheaper than the remedy. Most of them reduce to four things: sanitation, oxygen exclusion, nitrogen sufficiency, and not bottling a fermentation that has not finished.
The diagnosis is only worth the time if it changes a decision next season. Record what the fault was, what the batch record says was happening when it appeared, and which of the four it belongs to.
Why it matters: Cider is annual. A fault that is not attributed recurs, and it recurs a year later when the details have been forgotten.
Go deeper
- Sanitation — The single largest preventable cause across the fault list.
- Topping up — Oxygen exclusion, which is mostly a matter of headspace.
- The nitrogen problem in cider juice — The deficiency behind a whole family of fermentation faults.
- Sanitation: clean, sanitised, and why it decides the batch — The practical version, at the scale of one vessel.
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.
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.
Where to go next
Guides that follow on from this one.
When the fermentation is not doing what it should
My fermentation is doing something strange. What is going on?
Working safely: pressure, fruit and gas
What is actually dangerous about making cider?
What to measure, and what each number tells you
What should I be measuring, and what do the numbers mean?
How to taste cider and perry
How do I taste cider properly?
Questions this answers
Shown so you can tell whether this is the guide you wanted.
- Why does my cider smell of vinegar?
- Why has my cider stopped fermenting?
- Why is my cider cloudy?
- Can a faulty cider be saved?
- My cider smells of rotten eggs — what is it?
- How do I stop my cider going wrong next time?
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.
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.
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.