Fault
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.
Also called musty taint, rotten fruit character.
A musty or rotten-fruit taint in juice or cider is a signal to ask about patulin, a mycotoxin produced by Penicillium expansum in rotting apples. Patulin is not destroyed by pasteurisation and it concentrates in juice pressed from affected fruit, so a batch made from visibly rotten fruit should not be treated as safe simply because it has been heated or has fermented. Sorting rot out before milling is the effective control. Unfermented juice is the greater concern, and juice made from rotten fruit should not be given to children. See the patulin record for what the authorities say. This note is not a claim that all mouldy-smelling cider is hazardous — a musty cellar taint from a damp press cloth carries no such implication — but the two causes look similar from the glass, and the fruit needs to be ruled out rather than assumed.
- Severity
- Serious — the batch may not be salvageable
- Where it starts
- Harvest, Fruit preparation, Pressing, Maturation
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Harvest, Fruit preparation, Maturation, Storage
- Signs
- 6 recorded
What it is
Mould taint is a musty, earthy or damp-cellar character in cider, arriving either from fruit that was rotten when it was pressed or from mould growing on wooden vessels, cloths, crates or cellar surfaces. Sensorily it ranges from a faint dampness to an unmistakable rotten-fruit or mushroom note. Its more important dimension is that mouldy fruit, specifically fruit affected by Penicillium expansum, is the source of patulin, and a cider or juice made from rotten fruit raises a food-safety question that a taste description does not answer.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
On the nose
- A musty, damp-cellar or old-cardboard smell
- An earthy or mushroom note distinct from the earthiness of some cider fruit
- A rotten or over-ripe fruit character with a hollow, unpleasant edge
On the palate
- A flat, dulled palate, with the taint suppressing everything else
To look at
- Visible mould on fruit, crates, cloths or vessels — The most useful sign, and the one that appears before the cider does.
How the batch behaves
- Cider that foams excessively on opening — Mould-derived proteins are an established cause of gushing in brewing, and the parallel applies here.
The words for it: Musty, Damp cellar, Mushroom. Each links to what produces it.
When it appears. From the fruit if rot went into the mill, or from the cellar and the vessels if it did not. A taint present from the press and one that developed in a cask are different problems with the same smell.
Detectable at very low concentration, and the compounds responsible are stable — so once present it will not fade. The important corollary is that a cider tasting of mould is evidence that rot reached the process, which raises the separate and unsmellable question of patulin.
European Union; assimilated into UK law and maintained by The National Archives, Andrew Lea
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.
- Cork taint — Whether it affects the whole batch or single bottles. Cork taint is bottle-by-bottle; a mould taint from fruit or cellar affects everything.
- Brett character — Mould taint is damp cellar, mushroom and musty; Brett is barnyard, leather and sticking plaster. Brett is alive in the cider and will develop; a taint is static.
- Patulin contamination — A shared cause with different consequences. Mould taint is a flavour problem you can taste; patulin is a food-safety problem you cannot, and rotten fruit produces both.
- An old, damp cellar — Smell the room. A cellar taint transfers to everything stored there and to nothing bottled elsewhere.
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.
Several distinct routes produce musty character. Geosmin and 2-methylisoborneol are potent earthy-musty compounds produced by moulds and by actinomycetes, detectable at extremely low concentrations and capable of tainting a batch from a small amount of affected fruit. Chloroanisoles, formed when moulds methylate chlorophenols, give the damp-cardboard character usually associated with cork taint and can arise anywhere chlorine-based products have met wood or phenolic material.
The fruit moulds themselves are Penicillium expansum, the blue mould of stored apples and the principal producer of patulin; Botrytis cinerea, the grey mould; and Monilinia fructigena, the brown rot that turns fruit to a firm brown mass on the tree. Each contributes its own metabolites, and each degrades the fruit tissue so that the juice pressed from it carries breakdown products as well as taint compounds.
Patulin is the reason this matters beyond flavour. It is a mycotoxin produced chiefly by Penicillium expansum in rotting apples, it is stable to pasteurisation, and it concentrates in juice pressed from affected fruit. Its behaviour and the limits set for it are covered in the patulin record; the relevant point here is that a mouldy taint in juice is a signal to ask that question directly.
Cellar-borne mould works differently: it grows on damp wood, on cloths left wet, on crates and on walls, and it taints by contact and through the air. Wooden vessels and press cloths are the classic reservoirs, and a taint that appears in every batch from one cellar is usually environmental rather than agricultural.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Rotten and mouldy fruit going into the mill unsorted | Harvest | common |
| Windfalls collected from wet ground and stored before pressing | Harvest | common |
| Fruit stored too long, or stored damp, before milling | Fruit preparation | common |
| Press cloths left damp between pressings | Pressing | common |
| Mouldy wooden vessels, crates or cellar surfaces | Maturation | occasional |
| Chlorine-based cleaning products used around wood and phenolic material, producing chloroanisoles | Maturation | 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 |
|---|---|---|
| Address the source | Reliable | Finding whether the taint came from the fruit or from the cellar is the only useful action, because it determines whether next season’s problem is at the sorting table or on the cellar wall. |
| Discard juice pressed from substantially rotten fruit | Reliable | Where a batch was made from fruit with significant rot, the taint is the least of the reasons not to keep it. See the patulin record and the safety note below. |
| Fine with activated carbon | Unlikely to work | Adsorbs some taint compounds, and adsorbs everything else along with them. The result is usually a cider that is both tainted and stripped. |
| Blend into a much larger sound volume | Unlikely to work | Thresholds are so low that the dilution required generally taints the sound cider rather than rescuing the affected one. |
| Remove musty taint compounds from cider | Not possible | Geosmin, 2-methylisoborneol and the chloroanisoles have extremely low thresholds and cannot be removed by any means available to a small producer. |
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
- Sort fruit properly and discard anything with visible rot; this addresses the taint and the patulin question together.
- Cut out and reject brown-rotted fruit rather than trusting that fermentation will handle it.
- Keep the interval between collection and pressing short, and store fruit dry and ventilated.
- Wash, dry and store press cloths properly between uses, and replace them when they cannot be got clean.
- Keep the cellar dry and ventilated, and deal with mould on walls and surfaces rather than working around it.
- Avoid chlorine-based sanitisers around wood and phenolic material, since the chlorophenols they form are the precursors of musty chloroanisoles.
Mould taint is the fault where sensory assessment and food safety meet, and the two need to be held apart while both are taken seriously. Musty cider from a damp cellar is an unpleasant drink. Musty cider from rotten fruit is an unpleasant drink that also raises a mycotoxin question, and only inspection of what went into the press distinguishes them.
The commonest source in small-scale production is windfalls. Fruit collected off wet ground, sometimes days after it fell, carries soil, mould and rot, and pressing it whole means pressing all of that. Shaking fruit down and collecting it promptly is a different practice from gathering whatever is lying under the tree.
The cellar side of the fault is more tractable than makers expect. Press cloths are the single worst offender — porous, repeatedly wetted, often stored damp — and replacing a set of cloths has resolved more persistent musty taints than any treatment of cider ever has.
The chlorine point deserves emphasis because it is counter-intuitive. Chlorine-based sanitisers are effective, and around wood and phenolic material they can produce chlorophenols that moulds convert into chloroanisoles, which are among the most potent musty taint compounds known. Using a different class of sanitiser in a cellar containing wood is a cheap precaution.
The compounds involved
Patulin
A mycotoxin produced by the blue mould that rots stored apples, regulated in apple juice worldwide, and the clearest food-safety reason not to press rotten fruit.
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.
Aspergillus species
A large genus of storage moulds, more important in warm climates than in northern cider regions, and a source of musty taint and of mycotoxins other than patulin.
Where in the process it arises
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.
Windfall management
Deciding which fruit that has reached the orchard floor can be used, and getting the rest out of the crop before it becomes a patulin problem.
Fruit storage before milling
Holding a gathered crop between harvest and the mill, and managing what respiration, water loss and spoilage do to it while it waits.
Fruit washing
Removing soil, grass, stones and surface contamination from gathered fruit, usually in a water flume, before it reaches the mill.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Patulin control
Managing the mycotoxin produced by rot fungi in damaged apples, which is controlled by fruit selection rather than by any treatment applied to juice.
Faults it is confused with
These present similarly. What separates them is set out on each page.
Patulin contamination
Contamination of juice or cider with patulin, a mycotoxin produced by *Penicillium expansum* in rotting apples — a genuine food-safety question rather than a flavour one.
Cork taint
A damp-cardboard, wet-newspaper mustiness from trichloroanisole, usually carried by a natural cork but capable of reaching cider by other routes.
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.
Plastic and packaging taint
Plastic, rubber, adhesive or chemical notes picked up from unsuitable containers, liners, hoses, gaskets or cleaning residues.
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.
How cider is made, start to finish
How is cider actually made?
How to taste cider and perry
How do I taste cider properly?
Making perry
How do I make perry, and what is different about it?
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 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 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.
- How do cider makers keep patulin out — By sorting rotten fruit out before milling, because patulin comes from moulds growing on damaged apples. Fermentation reduces what gets through, so fermented cider carries no limit where juice does.
- How do i sterilise cider bottles — Wash them clean first, then sanitise with a no-rinse sanitiser or a sulphite solution, and fill while still wet with it. Bottles that look clean but have dried deposits inside are the usual source of bottle spoilage.
- What is cork taint — Cork taint is a musty, damp-cardboard smell caused mainly by trichloroanisole, which can come from the cork or from the cellar. It strips aroma from the drink even below the level at which it can be identified.
- Can you use windfall apples for cider — Traditional cider making relies on fruit gathered from the ground, and there is nothing wrong with it if it is sound. Rotten fruit is a different matter: brown rot carries patulin into the juice and should be discarded, not pressed.
- How long can apples be kept before pressing
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 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.
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.