Organism
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.
- Kind
- Mould
- Binomial
- Aspergillus spp.
- Role
- Spoilage
What it does
- Rots damaged and over-ripe fruit in store, particularly where storage is warm, with A. niger producing the black sporing rot familiar on decaying fruit.
- Tolerates lower water activity than most rot fungi, so it grows on dried and drying material and on store surfaces where other moulds do not.
- Produces musty, earthy and mushroom-like volatiles that transfer into pressed juice and are perceptible well below the point at which the mould itself is obvious.
- Includes mycotoxigenic species, though the mycotoxin of concern in apples specifically is patulin from Penicillium expansum; Aspergillus toxins are a greater concern in other commodities and climates.
- Colonises equipment, walls and wooden surfaces in damp buildings, and can taint cider by air rather than through the fruit.
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 | Favours warmth: most species grow fastest between 25 °C and 37 °C, which is why the genus is a lesser concern in cool northern stores than *Penicillium*. |
| pH | Tolerates fruit and juice acidity. |
| Oxygen | Aerobic; it grows on fruit and surfaces, not in the ferment. |
| Alcohol tolerance | Not applicable; it does not grow in cider. |
What it produces
Compounds this organism makes. Which organism made a compound usually decides whether it reads as a feature or as a symptom.
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.
Citric acid
A minor acid in apples and a much more significant one in pears, whose metabolism by lactic bacteria is the reason perry gains more butter and more vinegar from malolactic fermentation than cider does.
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
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.
Microbial haze
Cloudiness caused by a growing population of spoilage organisms, and therefore a symptom of something worse rather than a clarity problem in itself.
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.
Where in the process it appears
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 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.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Cellar storage
Holding packaged cider in conditions that let it change slowly and predictably, where stability of temperature matters more than the temperature itself.
Fermentation vessels
The container a cider ferments in — wood, stainless, plastic, glass or concrete — and how its permeability, thermal mass and resident microflora shape the result.
Juice storage
Holding unfermented juice sound between pressing and fermentation, by chilling, sulphiting, gas blanketing, freezing or aseptic filling.
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.
About Aspergillus species
Aspergillus is the genus that fills the gap Penicillium leaves in a warm climate. Where blue mould thrives in a cold store, Aspergillus species prefer warmth and lower moisture, and they become correspondingly more important in cider made in Mediterranean, southern-hemisphere and continental-summer conditions than in a damp Herefordshire barn.
For cider its principal contribution is taint rather than toxin. The genus is a prolific producer of musty and earthy volatiles, and these carry into juice at concentrations well below those needed to make the mould visible. A mouldy note in a cider is frequently traceable to fruit that was stored a little too long in a little too much warmth, or to a damp building with mould growth on walls and equipment — the second route being one a cellar audit finds and a fruit inspection does not.
On mycotoxins, the honest statement is a boundary. Some Aspergillus species produce ochratoxin A and aflatoxins, and those are serious contaminants in the commodities where they occur. The mycotoxin that matters in apples and apple juice is patulin, and its principal producer in pome fruit is Penicillium expansum. CiderHQ says that plainly rather than transferring concern from one commodity to another.
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 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.
- How should i store cider — Cool, dark and at a steady temperature. Light causes light-strike in clear glass, warmth accelerates oxidation, and temperature swings push cider past the closure of a bottle that is not tightly sealed.
- What should i ferment cider in — Anything inert, cleanable and closable: glass demijohns, food-grade plastic, stainless steel, or a wooden cask if you can keep it sound. Vessel shape and material change how much oxygen the cider sees and how fast it clears.
- 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.
- How long can apple juice sit before i ferment it — Only hours at room temperature before wild fermentation begins. Chilled and sulphited it can be held for a day or two; beyond that it needs freezing, pasteurising or fermenting.
- How long can apples be kept before pressing
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.
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.