Glossary · Chemistry
Esters
Definition
Compounds formed between an alcohol and an acid, produced in quantity by yeast during fermentation, and responsible for much of a cider’s fruity aroma.
- Subject
- Chemistry
In more detail
The characteristic cider esters include hexyl acetate and 2-methylbutyl acetate, which read as fresh apple, isoamyl acetate, which reads as banana and pear drop, and a series of ethyl esters of fatty acids giving apple, pineapple and waxy notes. Their formation is favoured by cooler fermentation and by particular yeast strains.
Esters are not stable. They hydrolyse slowly towards equilibrium in the bottle, which is why a young cider’s bright fruit fades over a year or two while other, slower characters emerge.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Chemistry
Hexyl acetate
The apple-skin and pear ester that is genuinely carried in from the fruit rather than made by the yeast, and one of the few fresh-fruit aromas that survives fermentation.
Chemistry
Isoamyl acetate
The banana and pear-drop ester, made by yeast from isoamyl alcohol, and one of the clearest chemical signatures of a warm fermentation.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Chemistry
Ethyl acetate
The ester of ethanol and acetic acid. At low concentration it reads as fruity and solvent-like; at higher concentration it is the nail-varnish note that accompanies acetic spoilage.
Sensory
Pear drop
A descriptor for the confectionery-solvent aroma of isoamyl acetate and related esters. Common in fast, warm fermentations and in some yeast strains; not a marker of pear content.
Chemistry
Higher alcohols
Alcohols larger than ethanol, formed by yeast from amino acids. In moderation they add complexity and a warm, slightly solvent note; in excess they read as harsh and heady.
Fermentation
Fermentation
The conversion of sugar to ethanol and carbon dioxide by yeast, together with the many secondary reactions that occur alongside it and which supply most of a cider’s aroma.
Fermentation
Maturation
The period after fermentation in which a cider settles, clarifies and changes chemically — esters forming and hydrolysing, phenolics polymerising, harsh notes integrating — before it is packaged or drunk.
Where to go next
- Cider glossary — The whole vocabulary, by subject and A–Z.
- Comparisons — Terms that are only really clear when set against the thing they are not.
- Search — Finds terms by their aliases and by their spellings in other languages.
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.
Washington State University cider research programme
Washington State University Northwestern Washington Research and Extension Center · university · passage verified 2026-08-24
The single most useful open cider dataset CiderHQ has found. The programme’s cultivar performance database gives juice chemistry, orchard behaviour, bloom and harvest timing and cider-maker tasting notes for 73 cultivars grown at one maritime site over fifteen years, and — unusually — publishes its classification thresholds alongside its figures, so the classification can be checked rather than taken on trust. It also states outright that its results diverge from the English ones. Read in full on 2026-08-24 and transcribed into `data/trials/wsu-mount-vernon.ts`; four published figures were found to be impossible and are withheld there with their reasons.