Organism
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.
Also called blue mould rot.
- Kind
- Mould
- Binomial
- Penicillium expansum
- Role
- Spoilage
What it does
- Infects fruit through wounds — picking damage, bruises, insect punctures, stalk-end tears — rather than through intact skin, so its incidence is a direct consequence of how fruit is handled.
- Macerates tissue with pectinolytic enzymes, producing the soft, watery, light-brown rot with blue-green sporing patches that gives it its common name.
- Synthesises patulin, a mycotoxin that passes into pressed juice and for which regulatory limits exist in apple juice in the EU, the UK and the Codex standard.
- Sporulates prolifically in store, so a single rotting fruit contaminates the ones around it and the store surfaces for the following season.
- Produces earthy and musty volatiles that carry into the juice, contributing mould taint independently of the toxin.
Conditions it works in
What the organism tolerates and what suppresses it. These are the levers a maker actually has: temperature, acidity, air, alcohol and sulphite.
| Condition | What is recorded |
|---|---|
| Temperature | Grows from around 0 °C to 25 °C and is notably active in cold store, which is why refrigerated storage slows but does not stop blue mould rot. |
| pH | Tolerates fruit and juice acidity throughout. |
| Oxygen | Aerobic; growth is on and in the fruit, not in the ferment. |
| Alcohol tolerance | Not applicable — it does not grow in fermenting or finished cider. |
| Sulphite tolerance | Sulphite in juice does not remove patulin already formed, though it reacts with it to some extent; sulphiting is not a patulin control. |
What it produces
Compounds this organism makes. Which organism made a compound usually decides whether it reads as a feature or as a symptom.
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.
Pectin lyase
The chain-cutting activity in a commercial pectinase preparation, which raises press yield and clears a juice by destroying the colloid pectin creates — and destroys the possibility of keeving in the same stroke.
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.
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
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.
Excessive sediment
More deposit in the bottle or vessel than the presentation intends, ranging from a normal conditioning yeast layer to a loose sludge that clouds every pour.
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 in the process it appears
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 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.
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 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.
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.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Hand harvesting
Taking fruit off the tree by hand into bags and bins, so that it arrives at the store undamaged and with its stalk intact.
Sweating the fruit
Deliberately heaping or storing gathered fruit so that it softens, loses water and finishes converting starch before it goes to the mill.
Pest and disease management
Keeping scab, canker, rots and the main insect pests to a level the orchard can carry, at a cosmetic standard well below dessert fruit but without allowing rot into the crop.
Shaking and collecting
Bringing fruit down with a pole or letting it fall, then gathering it from the orchard floor — the traditional way most cider and perry fruit has always been harvested.
Mechanical harvesting
Using trunk shakers, over-the-row machines or sweeper-elevators to bring down and lift a cider crop at a rate no hand crew can match.
About Penicillium expansum
Blue mould is the commonest post-harvest rot of apples worldwide and the reason patulin exists as a regulated contaminant in apple juice. Penicillium expansum is a wound pathogen: it does not penetrate sound skin, and it gets in wherever fruit has been bruised, punctured or torn. That makes its incidence a direct function of harvesting and handling — how fruit is picked, how far it falls, how long it sits, and whether damaged fruit is separated out before milling.
Patulin is the reason this matters beyond flavour. The toxin is produced in the rotted tissue and passes into pressed juice, and limits for it in apple juice are set in EU and UK law and in the Codex standard. CiderHQ does not quote the figures in this record because the `Organism` type carries no `measurements` field to give them their proper context; they belong on the compound and fault records, which can.
What reduces patulin is removing rotten fruit, and very little else does reliably. Washing helps with surface contamination but not with toxin already inside the fruit. Fermentation reduces patulin substantially — yeast metabolises and adsorbs it, and it reacts with sulphur dioxide — but this is a mitigation of variable extent, not a treatment, and it does not license pressing rotten fruit. Clarification and fining remove a further part. The intervention that works is at the sorting table.
There is a traditional counter-argument worth acknowledging honestly: some old cider practice regarded a proportion of over-ripe and partly rotted fruit as contributing to flavour, and sweating fruit to soften it before milling is a real and legitimate traditional technique. Sweating is not rotting. The distinction is between controlled softening of sound fruit and mould growth on damaged fruit, and only the second produces patulin.
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.
- 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.
- Why is there sediment in the bottom of my cider bottle — In a bottle-conditioned cider the sediment is yeast and is expected — pour carefully and leave the last centimetre. In a filtered cider it means something has grown since bottling.
- 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 are cider apples picked
- How is apple juice clarified before fermentation
Where to go next
- All organisms — Grouped by what each does in the ferment, and by what kind of organism it is.
- Compounds — The chemistry this microbiology produces.
- Troubleshooting — Work from the symptom in the glass back to the organism.
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.
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.
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
NIAB (incorporating East Malling Research)
NIAB · research institute · retrieved 2026-08-24
East Malling developed the M-series apple rootstocks that determine tree size in essentially every modern orchard, cider orchards included. The authority CiderHQ uses for rootstock behaviour.
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.