Sensory descriptor
Musty
A stale, mouldy, damp-loft note from fungal metabolites on the fruit or in storage, recorded as a taint.
Also called Mouldy, Stale.
- Aroma family
- Earthy
- Does it indicate a fault?
- It depends on the style it is met in
What causes it
Mustiness in cider is caused by fungal metabolites reaching the liquid, principally geosmin, 2-methylisoborneol and 1-octen-3-ol. These arrive from mould-affected fruit — Penicillium, Botrytis and Aspergillus species on apples that have lain or been stored damp — and from mouldy storage materials such as sacking, wooden crates and straw. Thresholds are extraordinarily low: geosmin is detectable at a few nanograms per litre, so a very small quantity of affected fruit taints a whole batch, and the compound is not removed by fining or filtration.
There is no acceptable level. Because geosmin’s threshold is so far below any level at which it could contribute complexity, its detection means the fruit or the store was already substantially affected.
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.
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.
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.
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.
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.
Fruit washing
Removing soil, grass, stones and surface contamination from gathered fruit, usually in a water flume, before it reaches the mill.
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.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Pomace conditioning
Letting milled pomace stand before it goes to the press so that it drains better, presses faster and gives more 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.
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.
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 Musty
Musty is among the most economically serious faults in cider because it is introduced at the fruit stage, cannot be removed downstream, and originates in a step — sorting — that is often the first to be economised on at scale.
It is routinely confused with cork taint, which produces a similar impression through a different compound and affects individual bottles rather than batches, and with damp cellar, which is environmental and generally milder.
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.
Damp cellar
A cool, musty, faintly fungal note from moulds and film organisms in the maturation environment.
Mushroom
A distinctly fungal note from 1-octen-3-ol, produced by moulds on the fruit or by film yeast on the surface.
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 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.
- 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 long can apples be kept before pressing
- Does cider contain patulin — Patulin comes from mouldy fruit and is regulated in apple juice. Fermentation reduces it substantially, so fermented cider carries far less risk than unfermented juice made from the same fruit.
- 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
- 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.
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.
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.