Glossary · Chemistry
Tannin
Definition
In cider usage, the phenolic material responsible for bitterness and astringency, principally condensed tannins — procyanidins — built from catechin and epicatechin units.
- Subject
- Chemistry
In more detail
The trade word "tannin" is looser than the chemistry. Long Ashton classification thresholds are quoted as percentage tannin, measured historically as total phenolics by a permanganate or Folin method, which counts material that is not tannin in the strict sense. What matters sensorially is the size distribution of the procyanidins: short chains taste bitter, long chains bind salivary protein and taste astringent.
Cider apples carry several times the phenolic content of dessert apples, which is the single largest compositional difference between a West Country cider and one made from culinary fruit.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Chemistry
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Chemistry
Total phenolics
The single number used to summarise everything phenolic in a juice, useful for comparing fruit and misleading whenever it is used to predict how a cider will taste.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Chemistry
Procyanidin
A chain of flavan-3-ol units — mainly epicatechin, with catechin as a terminal unit — and the principal tannin of cider apples. Chain length determines whether it tastes bitter or astringent.
Chemistry
Polyphenol
The broad class of plant compounds carrying multiple phenol rings. In apples this includes procyanidins, hydroxycinnamic acids such as chlorogenic acid, flavonols, dihydrochalcones such as phloridzin, and anthocyanins in red-fleshed fruit.
Sensory
Astringency
A tactile sensation of drying, roughening and puckering in the mouth, caused by tannins binding and precipitating the proteins that lubricate the oral surfaces. It is a feeling, not a taste.
Sensory
Bitterness
One of the basic tastes, detected by receptors chiefly on the posterior tongue. In cider it comes principally from short-chain procyanidins and from certain phenolic acids.
Fruit
Bittersweet
In the Long Ashton classification, a cider apple low in acid — conventionally below about 0.45 per cent — and high in tannin, above about 0.2 per cent. Bittersweets form the structural base of West Country cider.
Chemistry
Oligomer
A molecule built from a small number of repeating units. Oligomeric procyanidins — roughly two to about ten flavan-3-ol units — are the fraction of cider tannin perceived mainly as bitterness.
Chemistry
Polymer
A molecule built from many repeating units. Polymeric procyanidins, long chains of flavan-3-ols, bind salivary proteins efficiently and are the fraction of cider tannin perceived as astringency rather than bitterness.
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.
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 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.
Long Ashton Research Station cider fruit analyses
National Fruit and Cider Institute / University of Bristol · research institute · registered as competent for this subject · covers 1903–2003
The foundational body of cider-fruit science in English. Long Ashton produced the acid-and-tannin classification that divides cider apples into sweet, sharp, bittersweet and bittersharp, and analysed hundreds of cultivars grown at its Somerset site. Its figures are historic measurements of specific fruit at a specific place, not universal constants — a distinction CiderHQ preserves in every measurement record that cites it.