Sensory descriptor
Mushroom
A distinctly fungal note from 1-octen-3-ol, produced by moulds on the fruit or by film yeast on the surface.
Also called Fungal, Button mushroom.
- Aroma family
- Earthy
- Does it indicate a fault?
- It depends on the style it is met in
What causes it
The mushroom volatile is 1-octen-3-ol, formed by fungal enzymes acting on linoleic acid, and it reaches cider by two routes. The first is mould-affected fruit — Botrytis cinerea, Penicillium expansum or Monilinia fructigena on the apples — which carries the compound and its precursors into the juice at pressing. The second is a film yeast or mould growing on the surface of a partly filled vessel, which produces it in situ. Its threshold is low, in the low micrograms per litre, so a small proportion of affected fruit is detectable in a large batch.
There is no level at which mushroom character is expected in cider. Its first appearance is a signal to check the fruit sorting and the ullage in every vessel, since both causes are progressive and neither improves on its own.
The compounds responsible
Where the molecule is established. Some descriptors in this lexicon name a compound the compound register does not yet hold a record for; those are named in the cause above instead.
The organisms that make it
Where a specific organism is implicated rather than the fruit. Naming one answers a different question from naming a molecule: what is in the cellar, rather than what is in the glass.
Botrytis cinerea
Grey mould: a broad-host-range fruit rot whose laccase enzyme oxidises phenolics and whose glucans make a juice difficult to clarify.
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.
What raises it
Processes that increase this character, or preserve it where it would otherwise be lost.
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.
Topping up
Refilling a maturing vessel as evaporation and racking losses lower the level, so that no significant surface of cider is ever left in contact with air.
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.
The fault it points at
Meeting this descriptor above a certain intensity is how the fault below is usually noticed first.
Fault
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.
About Mushroom
Mushroom is one of the more actionable fault descriptors because its two causes are both visible: rotten fruit can be seen on the belt, and a film can be seen on the surface of the liquid.
It is a common companion to the patulin risk from Penicillium expansum, and its presence in juice is a reason to review sorting practice regardless of the sensory outcome, since patulin itself has no smell.
Others in the earthy family
Farmyard, wet stone, damp cellar, mushroom.
Farmyard
The composite animal-and-straw note of volatile phenols with short-chain fatty acids, central to traditional farmhouse character.
Corked
The damp-cardboard mustiness of TCA from a contaminated cork, affecting single bottles rather than batches.
Musty
A stale, mouldy, damp-loft note from fungal metabolites on the fruit or in storage, recorded as a taint.
Damp cellar
A cool, musty, faintly fungal note from moulds and film organisms in the maturation environment.
Wet stone
A cool, damp, faintly mineral impression, in cider a product of low-level sulphur compounds and high acidity rather than of minerals.
Forest floor
Damp leaf, soil and fungal character in aged cider, from the combination of oxidised phenolics with low-level fungal volatiles.
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 much headspace should a cider fermenter have
- 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.
- Are apples washed before making cider
- Do you need to sort apples before pressing
- What does dissolved oxygen do to cider
Where to go next
- The sensory model — The thirteen structural dimensions and the twenty aroma families, in full.
- Compounds — The chemistry behind the words.
- Troubleshooting — When a perception turns out to be a problem, this is where it is diagnosed.
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.
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.