Compound
p-Coumaroylquinic acid
The second most abundant hydroxycinnamic ester in apple, and the reservoir from which the p-coumaric acid behind 4-ethylphenol is slowly released.
- Class
- Phenolics
- Formula
- Not a single molecule — see below
- How often it matters
- Specialist — met in particular circumstances
What it does in cider
- Stores p-coumaric acid in bound form, keeping it unavailable to microorganisms until an esterase frees it.
- Releases that acid gradually through fermentation and maturation, setting the pace at which phenolic character can develop.
- Oxidises under polyphenol oxidase, though less readily than chlorogenic acid because it lacks the second ring hydroxyl.
- Contributes marginally to bitterness in its own right.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
Faults it is implicated in
Being implicated is not the same as being a fault. Several of the compounds on this site are ordinary constituents of a sound cider and define a named fault only above a concentration.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
About p-Coumaroylquinic acid
Where chlorogenic acid is caffeic acid bound to quinic acid, p-coumaroylquinic acid is p-coumaric acid bound to the same partner, and in most apple juices it is the second most abundant member of the hydroxycinnamic ester pool. Its single ring hydroxyl makes it a poorer substrate for polyphenol oxidase than chlorogenic acid, so it survives the browning of a juice better and carries further into the finished cider.
Its interest is as a reservoir. 4-Ethylphenol, the compound most responsible for the sticking-plaster and horse-blanket end of cider aroma, is made from free p-coumaric acid, and free p-coumaric acid in a cider comes mostly from the slow hydrolysis of this ester. A cider therefore has a stock of potential phenolic character built in from the fruit, which will be realised or not depending on whether the organisms capable of using it are present.
This explains a pattern that otherwise looks arbitrary: two barrels of the same cider, both carrying Dekkera, can differ substantially in phenolic intensity depending on how much bound precursor the fruit supplied and how long the cider has had to release it.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Phenolics
Hydroxycinnamic acids
The family of small phenolic acids that browns a juice, and whose release from their esters supplies the raw material for every volatile phenol a cider can develop.
Phenolics
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.
Acids
Quinic acid
The second acid of apple juice, better known as the part of chlorogenic acid that is not caffeic acid, and a small but real contributor to the astringent grip of cider fruit.
Phenolics
4-Ethylphenol
The horse-and-sticking-plaster compound, made by *Dekkera* from a phenolic acid the fruit supplied, and the clearest case in cider of one molecule being a tradition in one glass and a fault in 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.
- What is brettanomyces — *Brettanomyces*, correctly *Dekkera* in its spore-forming form, is a slow yeast that ferments sugars other strains leave behind and produces volatile phenols smelling of farmyard, leather or sticking plaster. In cider it is common and not always unwanted.
- Is brett a fault in cider — It depends on the tradition and the level. A trace of *Brettanomyces* character is expected in much West Country and Spanish cider; at high concentration it flattens fruit and dominates everything else, and few would defend it then.
- What causes a farmyard or barnyard smell in cider — Usually 4-ethylphenol, made by Brettanomyces from hydroxycinnamic acids in the juice. Whether it is a fault depends on the cider: a trace adds complexity to a traditional cider and dominates a fresh fruit-forward one.
- What is maceration in cider making — Maceration is letting milled pomace stand before pressing, so that enzymes soften the tissue and phenolics and aroma move from the skins into the juice. It raises both colour and tannin, and raises the risk of oxidation with them.
- 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.
- What is chlorogenic acid in apple juice — It is the most abundant hydroxycinnamic acid in apples and the main substrate for enzymatic browning, so it is largely responsible for how brown a pressed juice goes and how quickly.
Where to go next
- All compounds — Grouped by what the fruit brings and what the ferment makes of it.
- Sensory — Every descriptor, with the compound or process that causes it.
- Microbiology — The organisms whose metabolism most of this chemistry belongs to.
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.
Institut national de recherche pour l’agriculture, l’alimentation et l’environnement (INRAE)
INRAE · research institute · retrieved 2026-08-24
French national agricultural research. Its Angers programme produced much of the published work on apple procyanidin chain length and on the relationship between polymer size, bitterness and astringency.
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.