Fault
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.
Also called patulin, mycotoxin contamination.
Patulin is a mycotoxin, and this is a food-safety matter rather than a question of flavour. It is produced by Penicillium expansum and related moulds in rotting apples, it cannot be tasted or smelled, and it is not destroyed by pasteurisation, so neither a sensory check nor heating the juice is a control. It is regulated: the Codex Alimentarius sets a maximum level for patulin in apple juice, and EU law sets maximum levels for apple juice and solid apple products, with a lower level for products intended for infants and young children; EFSA is the authority for the underlying risk assessment. Anyone selling apple juice should be working from the limit that applies in their jurisdiction and from a documented control, not from this page. The practical control for everyone is the same and it is effective: sort rotten fruit out before milling, cut nothing back into the batch, keep windfalls short of the ground for as little time as possible, and store fruit cool and dry. Unfermented juice is the greater concern, because alcoholic fermentation substantially degrades patulin — a real mitigating fact for cider, but not a reason to press rotten fruit. Juice pressed from visibly rotten apples should not be given to children.
- Severity
- Safety — there is a real hazard here
- Where it starts
- Harvest, Fruit preparation, Orchard
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Harvest, Fruit preparation, Pressing
- Signs
- 5 recorded
What it is
Patulin is a mycotoxin produced by moulds growing on damaged and rotting fruit, above all by Penicillium expansum, the blue mould of stored apples. It is not detectable by taste or smell, it is not destroyed by pasteurisation, and it passes into juice pressed from affected fruit. It is the principal food-safety reason to sort rot out of a crop, and it is regulated internationally: the Codex Alimentarius sets a maximum level for patulin in apple juice, and the EU sets limits in law, with a lower limit for products intended for infants and young children.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
On the palate
- Nothing detectable in the finished drink at all — Patulin has no odour or flavour at the concentrations of concern. This is the single most important thing to know about it: sensory assessment cannot find it.
To look at
- Visible blue-green mould with a soft, watery brown rot on the fruit — *Penicillium expansum* rot is soft, sunken and readily separates from healthy tissue; the mould sporulates blue-green.
How the batch behaves
- A high proportion of damaged, bruised or long-stored fruit in the batch
- Windfalls gathered from wet ground days after they fell
On the nose
- A musty or rotten-fruit taint in the juice — A taint indicates rot was pressed; its absence does not indicate rot was not.
The words for it: Windfall apple. Each links to what produces it.
When it appears. Present from the fruit, and it does not appear later. Nothing downstream introduces it and nothing downstream removes it.
It is undetectable by taste, smell or appearance in the finished cider, which is the whole reason the control is at the fruit and the limits are regulatory. Fermentation reduces it partially and is not a control measure.
European Union; assimilated into UK law and maintained by The National Archives, EFSA, FAO / WHO
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.
- Mould taint — The critical distinction on this page. Mould taint is a flavour you can detect; patulin is a toxin you cannot. A cider that tastes clean is not evidence that the fruit was sound.
- Ordinary windfall fruit — Whether the fruit was rotten, not whether it was on the ground. Sound windfalls are ordinary cider fruit; visibly rotten fruit is the problem regardless of where it was picked from.
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.
Penicillium expansum infects apples through wounds — bruises, insect damage, stem punctures, and the injuries fruit receives falling and being handled. It cannot easily penetrate intact skin, which is why damage and rot go together, and why careful handling reduces the problem at source. Once established, it produces patulin as a secondary metabolite within the rotted tissue.
The toxin concentrates in and immediately around the rotted area. Because a rotted apple is soft and gives up its juice readily under pressure, the proportion of a batch’s patulin contributed by a small proportion of rotten fruit is disproportionate. Removing the rotten fruit removes most of the toxin.
Patulin is heat stable at the temperatures used for pasteurisation, so heating juice does not remove it. It is reduced by fermentation: alcoholic fermentation by Saccharomyces cerevisiae degrades patulin substantially, which means fermented cider generally carries far less than the juice it was made from. Unfermented apple juice is therefore the greater concern, and cloudy juice tends to carry more than clarified juice because clarification and fining remove some of it with the solids.
The toxicological assessment sits with the food-safety authorities. EFSA has evaluated patulin and it is regulated on that basis; Codex sets an international maximum level for apple juice, and EU law sets limits for apple juice, solid apple products and products intended for infants and young children. CiderHQ points to those instruments rather than restating a toxicological conclusion of its own.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Rotten and mouldy fruit pressed without sortingThe dominant cause, and the one entirely under the producer’s control. | Harvest | common |
| Windfalls collected late from wet ground | Harvest | common |
| Bruised and damaged fruit providing the wounds the mould needs | Harvest | common |
| Long or poor storage of fruit before milling | Fruit preparation | common |
| Fruit stored damp or in contaminated crates | Fruit preparation | occasional |
| Orchard practice allowing high levels of pest and disease damage to the crop | Orchard | 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 |
|---|---|---|
| Sort the fruit and reject the rot | Reliable | The only genuinely effective control, and it happens at the sorting table before milling. Every other intervention is partial. |
| Discard juice pressed from substantially rotten fruit | Reliable | Where a batch of unfermented juice was made from visibly rotten fruit, the honest answer is not to drink it and not to give it to anyone else, particularly children. |
| Ferment the juice | Partial | Alcoholic fermentation degrades patulin substantially, which is why fermented cider generally carries much less than the juice it came from. This is a mitigating fact about fermented cider, not a treatment to be relied on for a batch known to be contaminated. |
| Fine or filter the juice | Partial | Clarification and treatment with adsorbents remove some patulin along with the solids, and the effect is variable. It is not a control that can be relied on without analysis. |
| Rely on pasteurisation, or on tasting and smelling the juice | Not possible | Neither works. Patulin is heat stable at pasteurisation temperatures, so heating the juice makes it microbiologically safer while leaving the toxin untouched; and it is odourless and tasteless at the concentrations of concern, so a sensory check cannot be used as a control. |
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 rigorously before milling and reject fruit with any soft rot; cutting out a rotten patch is not sufficient, because the toxin extends into apparently sound tissue around it.
- Handle fruit to minimise bruising, since wounds are the route of infection.
- Shorten the interval between fruit falling or being picked and being milled.
- Store fruit cool, dry and ventilated, and inspect stored fruit for developing rot.
- Wash fruit and use clean crates and equipment, particularly where fruit has been on the ground.
- Where juice is being sold unfermented, treat patulin as a hazard requiring a documented control, and work from the limits and guidance that apply in the jurisdiction concerned.
Patulin is the one entry in this file that is genuinely about safety rather than about quality, and it deserves to be stated calmly. It is not a reason to be frightened of cider; it is a reason to sort fruit, and the practice that controls it is a practice good cidermakers follow anyway.
Two facts do most of the work. The first is that the toxin comes from rot, so the quantity in a batch is roughly proportional to how much rotten fruit went into the press — which puts the control entirely in the producer’s hands at the sorting table. The second is that fermentation degrades it substantially, so the risk sits much more with unfermented apple juice than with cider.
That second point matters for how the risk should be communicated. A great deal of anxious writing about patulin transfers a juice concern directly onto cider, which overstates it; a great deal of casual writing dismisses it entirely, which understates the juice case. The honest position is that the hazard is real, is regulated, is concentrated in unfermented juice from poor fruit, and is controlled by sorting.
The temptation the fault creates is the one to resist. A crop with a lot of rot in it represents money and work, and the instinct is to press it anyway and rely on fermentation, or to cut the bad parts out. Neither is a control: the toxin extends into tissue that still looks sound, and fermentation reduces rather than eliminates. Rejecting the fruit is the answer.
The compounds involved
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.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
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.
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.
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.
Juice pasteurisation
Heat treatment of juice before fermentation, which inactivates enzymes and microorganisms, and in doing so removes the wild flora that would otherwise ferment it.
Juice clarification
The deliberate use of enzyme, fining agents or mechanical separation to produce a bright juice before fermentation, and what that costs the ferment.
Faults it is confused with
These present similarly. What separates them is set out on each page.
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.
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.
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.
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.
- Which yeast ferments cider — Saccharomyces cerevisiae finishes almost every cider fermentation, whether it was pitched or arrived from the press house. In a spontaneous ferment it is not the first organism present, only the one that survives the alcohol it makes.
- 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.
- 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 is apple juice clarified before fermentation
- 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.
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.