Compound
Catechin
The minor flavan-3-ol of apple, present largely as the terminal unit of procyanidin chains, and consequently a useful analytical handle on chain length.
Also called (+)-catechin.
- Class
- Phenolics
- Formula
- C15H14O6
- How often it matters
- Occasional
What it does in cider
- Caps the end of most apple procyanidin chains, where epicatechin makes up the body of the chain.
- Contributes a milder bitterness than epicatechin in free form.
- Provides, through the ratio of terminal to extension units, the standard analytical route to mean degree of polymerisation.
- Oxidises under polyphenol oxidase alongside the other catechol-bearing phenolics.
How it is perceived
What the compound registers as, and at roughly what concentration. Perception is not a property of the molecule alone: sugar, tannin and carbonation all change where a threshold falls.
- mild bitterness
- slightly drying
Descriptors it is responsible for
Sensory records that name Catechin as a cause. Each states the perception and the mechanism behind it.
- Black tea — A dry, tannic, faintly leafy note from polymerised procyanidins with mild oxidative development.
The structure it moves
| Dimension | What it is |
|---|---|
| Bitterness | A taste sensed at the back of the tongue, distinct from the drying grip of astringency. |
| Tannin | The phenolic material that gives cider structure, grip and ageing capacity. |
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.
Juice oxidation
The enzymic browning that begins the moment apple juice meets air, which some traditions deliberately allow and others suppress.
Fining
Adding a reactive agent that binds a target colloid and carries it to the bottom, chosen according to whether the problem is tannin, protein or a phenolic taste fault.
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.
Oxidation
The cumulative effect of oxygen on finished cider: fruit aroma flattens, colour deepens towards amber, and a bruised-apple or sherry-like character replaces the fresh one.
Enzymatic browning
The rapid darkening of milled fruit and fresh juice as polyphenol oxidase converts phenolics to quinones, taking colour and some tannin structure with it.
Acrolein bitterness
An intense, lingering bitterness quite unlike tannin, produced when lactic acid bacteria convert glycerol to acrolein and the acrolein reacts with the cider’s phenolics.
Excessive astringency
A drying, roughening, mouth-puckering sensation that outstays its welcome, produced by larger phenolic polymers precipitating salivary proteins.
Excessive bitterness
Bitterness that dominates the palate rather than supporting it, usually from a blend weighted too heavily towards high-tannin fruit or extracted too hard.
Pinking
An unexpected pink or salmon tint developing in a pale cider or perry, associated with oxidation of colourless phenolic precursors.
Described in full
- Shape
- A horizontal axis of increasing average degree of polymerisation, marked with four positions: monomer and dimer at the left, tetramer in the middle, and long polymer at the right. Two labelled bands run across it — an astringency band that thickens steadily from left to right, and a bitterness band that is thin at the left, thickest at the tetramer, and thin again at the right.
- Astringency
- Increases with the degree of polymerisation. Longer chains carry more sites to cross-link salivary proteins, and it is the loss of lubrication in the mouth that reads as drying rather than as taste.
- Bitterness
- Peaks at the medium chain length. In the study behind this figure, the tetramer fraction was the most bitter of the four tested; both the shorter and the longer fractions were less so. Bitterness is a receptor event, and a molecule can be too large to fit the receptor while remaining perfectly able to bind a protein.
- The fixed condition
- Every point on this axis is 750 milligrams of procyanidin per litre in the same model solution of water, ethanol, fructose and malic acid. Concentration is held constant so that the axis shows chain length alone. The companion study found the chain-length effect is not identical at every concentration, so this figure describes one concentration.
- The side effect
- A note beneath the axis records that in the same experiments the perception of sweetness and sourness also moved with procyanidin concentration, although the fructose and the malic acid were identical in every sample. Tannin does not only add its own sensations; it changes the reading of the others.
- What this is not
- A model solution is not cider. It contains no pectin, no protein, no carbonation and none of the hundreds of compounds a fermentation makes, and every one of those can shift how a phenolic behaves on the palate.
About Catechin
Catechin and epicatechin are the same molecule with one stereocentre inverted, and in apples that small difference produces a marked division of labour. Epicatechin builds the chain; catechin, when it appears, tends to sit at the end of it. The consequence is analytical rather than sensory: because each chain carries exactly one terminal unit regardless of its length, measuring the proportion of terminal units in a phenolic extract gives the mean degree of polymerisation directly.
In free form catechin is bitter, but less so than epicatechin, and it is present in smaller quantity in most apple juices. Its contribution to how a cider tastes is real but modest, and it is nearly always met as part of a mixture rather than on its own.
It is worth distinguishing from the catechins of tea, which are largely gallated and behave differently: apple flavan-3-ols carry no gallate esters, which is one reason apple astringency is described as softer and rounder than the astringency of strong tea at comparable phenolic concentration.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Phenolics
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Phenolics
Epicatechin
The flavan-3-ol that apple procyanidins are almost entirely built from, and the most bitter of the phenolic monomers a cider contains.
Phenolics
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.
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 are procyanidins in cider — They are the condensed tannins of apples: chains of catechin-type units whose length decides how much of the phenolic load reads as bitterness and how much as astringency. Two ciders with identical total tannin can taste nothing alike.
- Is cider vegan — Cider itself is a plant product, but some producers clarify it with animal-derived finings such as gelatine, isinglass or chitosan. Vegan status therefore depends on the fining regime, which is why some ciders are certified and others are not.
- How are apples milled for cider
- Does cider contain antioxidants — Cider carries apple polyphenols, and tannic bittersweet ciders carry considerably more than pale ones made from dessert fruit. What that means for health is a clinical question this site does not adjudicate.
- 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.
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.
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.