Compound
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.
- Class
- Additives and processing aids
- Formula
- C7H6O4
- How often it matters
- Central to how cider behaves
What it does in cider
- Is produced by Penicillium expansum and some related moulds as they rot apple tissue, chiefly through wounds in stored or fallen fruit.
- Diffuses beyond the visible rot into apparently sound tissue, so cutting out a brown patch does not reliably remove it.
- Survives pasteurisation, because it is heat-stable at the temperatures juice processing uses.
- Is substantially degraded during alcoholic fermentation, so finished cider generally carries far less than the juice it was made from.
- Is controlled almost entirely at the fruit-sorting stage, which is why sorting is a food-safety operation and not merely a quality one.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
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.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
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.
Fruit washing
Removing soil, grass, stones and surface contamination from gathered fruit, usually in a water flume, before it reaches the mill.
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.
Wild fermentation
Letting the microflora already present on the fruit and in the press house carry the ferment, in a succession rather than as a single organism.
Inoculated fermentation
Starting a ferment by pitching a chosen yeast culture so that one known strain, rather than the fruit’s resident population, does the work.
Fining
Adding a reactive agent that binds a target colloid and carries it to the bottom, chosen according to whether the problem is tannin, protein or a phenolic taste fault.
Faults it is implicated in
Being implicated is not the same as being a fault. Several of the compounds on this site are ordinary constituents of a sound cider and define a named fault only above a concentration.
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.
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.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
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.
About Patulin
Patulin is a mycotoxin, and the organism that matters for apples is Penicillium expansum, the blue mould responsible for the soft brown rot that spreads from a bruise or a puncture in stored fruit. The mould needs a wound to get in, which is why the risk concentrates in exactly the fruit a cidermaker is most tempted by: windfalls that have sat on the ground, fruit knocked about in handling, and fruit held too long in store. Byssochlamys and some Aspergillus species also produce it, but in apple products the great majority comes from P. expansum.
Two properties make it a genuine hazard rather than a theoretical one. It diffuses. The toxin is not confined to the visibly rotted tissue, and trimming a lesion out of an apple removes the mould without reliably removing the toxin from the flesh around it. And it is heat-stable at juice-processing temperatures, so pasteurisation, which handles the microbiological risks of a fruit juice, does not handle this one. A pasteurised juice pressed from rotten fruit is a microbiologically safe product carrying a chemical contaminant.
The controls are therefore almost entirely mechanical and upstream. Sorting fruit before milling, rejecting rotten and heavily bruised apples rather than trimming them, washing and floating fruit to separate damaged from sound, handling fruit gently in the orchard and in store, and pressing promptly rather than holding fruit until it softens. Where a batch is nonetheless suspect, activated carbon treatment reduces the toxin, at the cost of stripping colour and aroma along with it. There is one piece of good news specific to cider: alcoholic fermentation degrades patulin substantially, which is why fermented apple products generally analyse far lower than unfermented juice from the same fruit. That is a mitigation and not a licence — it does not eliminate the toxin, and it does nothing for anyone making unfermented juice.
The regulatory position is settled and worth stating plainly. The Codex Alimentarius maximum level for patulin in apple juice is 50 micrograms per kilogram, and the assimilated Regulation 1881/2006, which sets contaminant limits in Great Britain, carries the same figure and — this is the part usually missed — gives cider a line of its own rather than covering it by analogy with juice. Entry 2.3.2 reads “spirit drinks, cider and other fermented drinks derived from apples or containing apple juice — 50”, in micrograms per kilogram. Solid apple products are held to 25, and apple products sold for infants and young children to 10,0. The FAO/WHO expert committee has set a provisional maximum tolerable daily intake in the region of 0.4 micrograms per kilogram of body weight, and EFSA has assessed the toxicology behind these figures. None of this makes cider a risky product — the fermentation step, the limits and ordinary fruit sorting between them keep exposure low — but it does mean that a producer pressing visibly rotten fruit is creating a regulated food-safety problem, not merely a poor-tasting cider.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Additives and processing aids
Sulphur dioxide
The antimicrobial and antioxidant on which most modern cidermaking depends, and whose effectiveness collapses as pH rises — which makes every sulphiting decision a pH decision first.
Acids
Galacturonic acid
The sugar acid that pectin chains are built from, released as they break down, and a significant part of why juice from rotten fruit binds so much of the sulphite added to it.
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.
- Does cider contain sulphites — Most does. Sulphur dioxide is added to protect juice and finished cider, and fermentation itself produces a small amount even when none is added. European labels must declare it above 10 mg per litre.
- How does cider ferment — Yeast consumes the sugar in apple juice and produces roughly equal masses of ethanol and carbon dioxide, along with the esters and higher alcohols that give cider much of its aroma. In a wild ferment several yeast species take turns before *Saccharomyces* finishes the job.
- Is cider vegan — Cider itself is a plant product, but some producers clarify it with animal-derived finings such as gelatine, isinglass or chitosan. Vegan status therefore depends on the fining regime, which is why some ciders are certified and others are not.
- Can you make cider from shop bought apple juice — Yes, provided the juice contains no preservative — check for potassium sorbate or benzoate on the label. Pasteurised juice ferments perfectly well once yeast is added, because pasteurisation removes the organisms but not the sugar.
- 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.
- Why does mouldy fruit matter for cider — Penicillium expansum is the blue mould of stored apples and the principal producer of patulin. Sorting rotten fruit out before milling is a food-safety step and not only a quality one.
Where to go next
- All compounds — Grouped by what the fruit brings and what the ferment makes of it.
- Sensory — Every descriptor, with the compound or process that causes it.
- Microbiology — The organisms whose metabolism most of this chemistry belongs to.
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
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.