Cider science
The difference between a fault and a style feature
Is that a fault or is it meant to taste like that?
In short
Usually it depends on the style and on how much of it there is. Volatile phenols, acetaldehyde, diacetyl, ethyl acetate and lactic character are all traditional signatures somewhere and faults elsewhere, and the molecule is identical in both cases.
Two things decide. The first is concentration relative to a perception threshold and to the point where the compound dominates. The second is what the style was meant to be: the same volatile acidity that is characteristic in sidra natural is a defect in a fresh sparkling cider.
A short list of characters are faults everywhere: hydrogen sulphide and mercaptans, mousiness, ropiness, geranium taint, cork taint, light-strike, and any character indicating that a container has failed.
The two questions to ask
The first question is whether the character dominates. Almost every fault compound contributes something at low concentration and takes over above it, and the interval between the two is often narrow. Ethyl acetate at low levels adds lift; above threshold it is nail varnish and nothing else can be smelt. A useful assessment therefore reports the level as well as the presence.
The second question is what the drink was intended to be. This is not a matter of being charitable to the producer; it is a matter of what the assessment is for. A cider whose category is defined by oxidative maturation cannot sensibly be marked down for oxidative character, and one whose category is defined by fresh fruit aroma cannot sensibly be excused it.
These two questions do most of the work. Where they disagree — a character that is appropriate to the style but present at a dominating level — the level wins, because a cider in which one compound dominates has lost the balance the style depends on.
Where the same compound sits differently
| Character | Compound | Where it belongs | Where it is a fault |
|---|---|---|---|
| Leather, smoke, sticking plaster | 4-ethylphenol and 4-ethylguaiacol, from Brettanomyces or lactic bacteria | Traditional English farmhouse and some Spanish and French ciders, at trace to moderate levels | Any cider built on fresh fruit character, and any cider where it dominates |
| Sherry, bruised apple | Acetaldehyde and phenolic oxidation products | Oxidatively matured traditional styles; ice cider | A cider intended to be fresh; at high levels, everywhere |
| Butter, butterscotch | Diacetyl, from malolactic fermentation | Traditional ciders that have undergone malolactic conversion | Fresh, fruit-driven ciders, where it reads as artificial |
| Vinegar and solvent | Acetic acid and ethyl acetate | Sidra natural, within a band that the tradition and its designation accept | Most other categories, and sidra natural above that band |
| Farmyard, damp cellar | Mixed microbial origin | Wild-fermented farmhouse cider | Any cider presented as clean and modern |
| Haze and sediment | Yeast, fruit solids, colloids | Unfiltered cider, sidra natural, bottle-conditioned cider | A cider that was clear when packaged and is not now |
The characters that are faults everywhere
- Hydrogen sulphide and mercaptans. No cider tradition treats rotten egg, drains or rubber as a feature.
- Mousiness, from tetrahydropyridines. Detected as an aftertaste rather than an aroma, often seconds after swallowing, and unwelcome in every category.
- Ropiness, where lactic bacteria produce a polysaccharide that makes the cider pour in a thread.
- Geranium taint, produced when lactic bacteria act on sorbate; it indicates that a stabiliser was used in the presence of live bacteria.
- Cork taint, from haloanisoles, which strips aroma and adds a musty character.
- Light-strike, from ultraviolet exposure through pale glass, giving sulphidic off-aromas.
- Acrolein bitterness, from bacterial degradation of glycerol.
- Any indication of container failure — a lifted crown cap, a bulging can, unexpected pressure in a still product.
Why this matters beyond assessment
The fault-or-feature question is where most of the bad faith in cider commentary lives. A character can be dismissed as a fault to disqualify a tradition, or excused as traditional to avoid confronting a poorly made drink, and both moves are made regularly.
The defence against both is to describe rather than to rule. Saying that a cider carries a marked phenolic character, that this is characteristic of its category, and that in this example it dominates the fruit is three separate statements, each of which can be examined. Saying that it is faulty, or that it is authentic, collapses all three into a verdict.
This site is built to keep them separate. Faults are recorded as compounds and mechanisms with signs and causes; styles are recorded with what defines them and what legitimately varies inside them; and where a character sits on both lists, both records say so.
Also answered on this page
Questions this page covers, so you can tell at a glance whether it is the one you want.
- Is Brett character a fault in cider?
- How much volatile acidity is acceptable?
- What is mousiness and why can I not smell it?
- Is a buttery taste in cider wrong?
Related
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.
- What is still unknown about cider — A great deal, and rather more than the confident tone of most cider writing suggests. Four gaps are large enough to affect what can honestly be said on almost any page of this site.
- Can you fix a cider that has gone vinegary — Not really. Volatile acidity cannot be removed at small scale, and blending it away only dilutes it. The realistic options are to accept it, to blend a lightly affected batch into a much larger sound one, or to let it finish becoming vinegar.
- What are the standard aroma categories for cider
- What does oxygen do to cider
- What is mousiness in cider — Mousiness is a fault caused by tetrahydropyridines produced by *Brettanomyces* and some lactic acid bacteria. It tastes of stale grain or a mouse cage and appears in the aftertaste rather than in the aroma.
- What is sidra natural — Sidra natural is the still, dry, unfiltered cider of Asturias and the Basque Country, bottled without added carbonation and poured from a height to rouse it. It is tart, funky and made to be drunk in small measures poured one at a time.
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 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.
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.
Denominación de Origen Protegida Sidra de Asturias
Consejo Regulador de la DOP Sidra de Asturias · designation authority · passage verified 2026-08-24
The regulating council for Asturian cider. Read on 2026-08-24, and it turned out to carry far more than a permitted-variety list: an agronomic and technological characterisation of each admitted variety, with total acidity, total polyphenols, vigour, flowering, ripening, cropping and susceptibility to fungal disease. The characterisation is credited to SERIDA’s fruit-research programme. Two things it settles are corrections to what CiderHQ previously held: Asturias sorts cider fruit into nine technological blocks rather than five, and it publishes acidity as sulphuric acid rather than malic. The figures are transcribed into `data/trials/serida-asturias.ts` and cite this source, because this is where they were read.