Sensory descriptor
Bruised apple
The brown, soft, faintly sweet note of enzymatic browning, met wherever apple tissue or juice has met air.
Also called Browned apple, Oxidised apple.
- Aroma family
- Oxidative
- Does it indicate a fault?
- It depends on the style it is met in
What causes it
When apple tissue is damaged, polyphenol oxidase meets chlorogenic acid and the other hydroxycinnamic acids in the presence of oxygen and converts them to quinones, which polymerise into the brown pigments of a bruise. The reaction consumes the fresh aldehyde fraction indirectly by consuming oxygen and generating reactive intermediates, and it produces its own soft, faintly sweet, distinctly brown aroma. In finished cider the same perception arises from acetaldehyde accumulation and phenolic oxidation, which is why bruised apple is both the first stage of the oxidative family and the most common single word for mild oxidation in cider.
Deliberate juice oxidation before fermentation — allowing the must to brown and the oxidised tannins to precipitate — is a traditional technique that removes harsh phenolics and produces a paler, softer cider. Oxidation in the finished drink is a different matter and takes freshness away without giving anything back.
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.
Polyphenol oxidase
The copper enzyme that turns cut apple brown within seconds, and the reason a cidermaker has to decide, at the press, whether to let the juice oxidise or to stop it.
Chlorogenic acid
The most abundant single phenolic in apple juice, the preferred substrate of the enzyme that browns it, and the precursor of one of the volatile phenols behind farmyard character.
Acetaldehyde
The compound sitting one step short of ethanol, which smells of bruised apple and sherry, binds most of the sulphite added to a cider, and is the chemical signature of oxidation.
Dissolved oxygen
Essential to a healthy yeast population at the start of fermentation and the principal enemy of a cider from the moment fermentation ends.
What raises it
Processes that increase this character, or preserve it where it would otherwise be lost.
Juice oxidation
The enzymic browning that begins the moment apple juice meets air, which some traditions deliberately allow and others suppress.
Milling
Reducing whole fruit to a pulp so that the press has cell walls it can drain, rather than intact apples it can only bruise.
Oxidative maturation
Ageing a cider with a deliberate, measured oxygen supply so that tannins polymerise and soften and an aldehydic character develops on purpose, which is not the same thing as the oxidation fault.
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.
Sulphiting
Adding sulphur dioxide to juice to suppress spoilage organisms and oxidative browning, at a level that only means anything once the juice pH is known.
The fault it points at
Meeting this descriptor above a certain intensity is how the fault below is usually noticed first.
Fault
The rapid darkening of milled fruit and fresh juice as polyphenol oxidase converts phenolics to quinones, taking colour and some tannin structure with it.
Where it is usually met
Fruit and styles this character is recorded in. A record here is where the descriptor is commonly found, not a claim that every example shows it.
About Bruised apple
This is the descriptor where the difference between controlled and uncontrolled oxidation is clearest. Browning the juice on purpose is an old and defensible technique; browning the cider is a failure of vessel management. The same word covers both and the stage at which it happened decides everything.
It is the first stop on the oxidative path, and its companions further along — walnut, sherry, cardboard — are the same process at greater extent.
Others in the oxidative family
Sherry, walnut, bruised apple, cardboard.
Sherry
A nutty, oxidised, faintly volatile character from acetaldehyde and sotolon in long-air-exposed cider.
Walnut
A dry, slightly bitter nut note from advanced phenolic oxidation, characteristic of long-matured tannic cider.
Wet cardboard
The flat, papery note of (E)-2-nonenal and related aldehydes, the sensory signature of oxidative staling.
Dried apple
Concentrated, leathery apple character from moderate oxidation, sitting between fresh fruit and full oxidative development.
Dried fruit
Raisin and sultana character from long oxidative ageing, most often met in concentrated and fortified styles.
Hazelnut
A lighter, sweeter nut note from early oxidative development and from lees contact.
Maderised
Heat-and-air damage together: cooked, browned, flat character from cider stored warm in the presence of oxygen.
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 are apples milled for cider
- Why is sulphite added to cider — Sulphur dioxide suppresses spoilage bacteria and wild yeast before fermentation and protects the finished cider from oxidation. How much of it is active depends strongly on pH, which is why low-acid juice is harder to protect.
- What is keeved cider — A cider made naturally sweet by starving the yeast rather than by adding sugar. Keeving strips nutrients out of the juice before fermentation, so the ferment slows and stops with fruit sugar still in it, and nothing has been put back.
- What is sidra natural — Sidra natural is the still, dry, unfiltered cider of Asturias and the Basque Country, bottled without added carbonation and poured from a height to rouse it. It is tart, funky and made to be drunk in small measures poured one at a time.
- How much headspace should a cider fermenter have
- Why does apple juice go brown when pressed — Polyphenol oxidase in the fruit reacts phenolics with oxygen the moment cells are broken, turning the juice brown. In cider making this is sometimes prevented with sulphite and sometimes encouraged, because it also drops harsh tannin out of solution.
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.
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.
Peer-reviewed literature on apple phenolics and cider sensory perception
Various journals · peer-reviewed literature · registered as competent for this subject
Registered as a class rather than as one paper, because the mechanisms CiderHQ describes — tannin chain length driving the split between bitterness and astringency, salivary protein precipitation, enzymatic browning — are established across many studies rather than resting on any single one. Individual papers are cited where a specific number is quoted.
Institut Français des Productions Cidricoles (IFPC)
IFPC · research institute · retrieved 2026-08-24
The French technical institute for cider production. The authority for the French cultivar classification families, for keeving as an industrial process, and for the pectin and nitrogen chemistry that keeving depends on.