Compound
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Also called Condensed tannins, Proanthocyanidins, Apple tannin.
- Class
- Phenolics
- Formula
- Not a single molecule — see below
- How often it matters
- Present in every cider
What it does in cider
- Binds salivary proteins and precipitates them, removing the lubricating film from the mouth: this is astringency, a mechanical sensation rather than a taste.
- Binds bitter receptors when the molecule is small enough to reach them, so short oligomers taste bitter while long polymers dry the mouth instead.
- Polymerises slowly through maturation and eventually precipitates, which is why a hard young cider softens with time and throws a sediment as it does.
- Provides oxidative buffering, giving tannic ciders far more resistance to air than low-tannin ones and making long ageing possible at all.
- Complexes with proteins in food as readily as in saliva, which is the mechanism behind the classic pairing of tannic cider with fat and protein.
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.
- drying
- grippy
- bitter
- chewy
- walnut skin
- tea-like
There is no single threshold, because two effects rise on different curves. Bitterness peaks with the smaller oligomers and falls as the polymer lengthens; astringency does the opposite, becoming perceptible only once chains are long enough to cross-link salivary proteins. Astringency also accumulates over successive sips instead of adapting away, so a cider that seems moderate on first taste can be markedly drying by the third.
Descriptors it is responsible for
Sensory records that name Procyanidins as a cause. Each states the perception and the mechanism behind it.
- Bittersweet apple — The soft, low-acid, faintly earthy ripe-fruit character of traditional West Country cider fruit, inseparable from its phenolic weight.
- Walnut — A dry, slightly bitter nut note from advanced phenolic oxidation, characteristic of long-matured tannic cider.
- Black tea — A dry, tannic, faintly leafy note from polymerised procyanidins with mild oxidative development.
- Citrus pith — A dry, bitter citrus note where phenolic bitterness sits alongside sharp acidity rather than behind fruit.
- Crab apple — A small-fruit character combining very high acidity, hard green aldehydes and a marked phenolic grip.
- Grapefruit — A bitter-edged citrus note from volatile thiols released by yeast, distinct from acid-driven lemon character.
- Leather — A dry, tanned-hide note from low levels of volatile phenols over well-polymerised tannin.
- Pear skin — A dry, gritty, faintly tannic pear note from the fruit’s skin and stone cells, prominent in traditional perry pears.
- Peppery bitterness — A harsh, burning bitterness from acrolein formed when lactic bacteria degrade glycerol.
- Red fruit — A general soft red-berry impression from medium-chain ethyl esters, most often met in tannic ciders with some age.
- Unripe pear — Hard, green, markedly astringent pear character from fruit pressed before it softened.
- Cherry — Dark stone-and-berry character combining benzaldehyde with heavier ethyl esters, met in aged tannic cider.
- Plum — Dark, soft stone-fruit weight from heavier ethyl esters combined with polymerised phenolics in matured cider.
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. |
| Astringency | The drying, rough sensation left after swallowing. |
| Tannin | The phenolic material that gives cider structure, grip and ageing capacity. |
| Body | How much weight and viscosity the drink has in the mouth. |
| Phenolic character | Smoky, spicy, leathery or medicinal aromas that sit apart from fruit. |
Measured figures
Shown as they were measured, with the context each was taken in. They are not averaged: a concentration recorded in one country's fruit in one decade is not a constant.
3 separate analyses of total tannin. They are shown as they were measured, in their own contexts, and are not averaged — the same fruit grown somewhere else can genuinely give a different number.
Total tannin0.050–0.600 % w/v
Long Ashton, Somerset, England, 1903–2003 · National Fruit and Cider Institute / University of Bristol
Historic juice analyses spanning dessert fruit at the bottom of the band to the most tannic bittersweets at the top. The figure is total tannin by a colorimetric method: it says nothing about how that tannin is distributed between short and long chains, and that distribution is what decides how the cider tastes.
Total tannin0.200 % w/v
context not recorded · Long Ashton classification threshold · National Fruit and Cider Institute / University of Bristol
The line that separates bittersweet and bittersharp fruit from sweet and sharp fruit under the English scheme. A convention chosen to be useful for blending, not a point at which anything changes chemically.
Total tannin2.4 g/L
Normandy and Brittany, France · Thiolysis and HPLC of centrifuged juices from French cider apple varieties · Guyot, Marnet, Sanoner and Drilleau, Journal of Agricultural and Food Chemistry 51(21):6240–6247
The upper figure the study reached, in centrifuged juice — that is, after the solids that carry much of the phenolic load have been taken out. It is a ceiling observed in a variety trial, not a typical juice: most of the fruit measured sat well below it, and variety was the largest single source of variation.
The phenolic fraction responsible for bitterness and astringency. Measured in percent weight per volume.
Procyanidin chain length25.00 :1
Normandy and Brittany, France · Average degree of polymerisation by thiolysis, one variety, centrifuged juice · Guyot, Marnet, Sanoner and Drilleau, Journal of Agricultural and Food Chemistry 51(21):6240–6247
A twenty-five-unit average chain, dissolved in the juice at close to 1.2 g/L. This matters because the intuition that big polymers fall out of solution is wrong here: they stay in, and they arrive on the palate. The same study found that the average chain length in juice is significantly shorter than in the fruit it came from, so pressing itself shifts the distribution.
The average degree of polymerisation, which decides how much of the phenolic load reads as bitterness and how much as astringency. Measured in ratio.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
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.
Maceration
Holding milled pomace before pressing so that phenolics, aroma precursors and pectin have time to move out of the solid tissue and into the juice.
Pomace conditioning
Letting milled pomace stand before it goes to the press so that it drains better, presses faster and gives more juice.
Tannin balancing
Setting the phenolic structure of a blend, which means handling bitterness and astringency separately because they are different perceptions produced by different sizes of the same molecules.
Blending
Combining separate lots of cider or perry into one, which in cider is the historically normal way of making the drink rather than a remedy applied when single lots disappoint.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
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.
Juice oxidation
The enzymic browning that begins the moment apple juice meets air, which some traditions deliberately allow and others suppress.
Tank maturation
Resting cider in stainless steel or a lined vessel, where the point of the container is that it contributes nothing and admits almost no oxygen.
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.
Filtration
Passing cider through a porous medium to reach a stated visual brightness, at a real cost in colloidal material, body and aroma.
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.
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.
Excessive astringency
A drying, roughening, mouth-puckering sensation that outstays its welcome, produced by larger phenolic polymers precipitating salivary proteins.
Thin body
A cider with no weight or texture in the mouth, most often from over-watered pomace, low-gravity juice or a blend with nothing to give it substance.
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.
Colour loss
A cider left noticeably paler than it should be, usually because fining, filtration or sulphite has removed the phenolic material that gave it colour.
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.
Protein haze
A fine haze that forms as protein and tannin combine into insoluble complexes, often appearing in a cider that had already been clear.
Metal haze
A haze or dark cast caused by dissolved iron or copper picked up from equipment, forming insoluble complexes with phosphate or with the cider’s phenolics.
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 Procyanidins
A procyanidin is a chain of flavan-3-ol units joined end to end. In apples those units are overwhelmingly (−)-epicatechin, with (+)-catechin appearing mostly at the end of a chain, and the links are carbon–carbon bonds that acid and enzymes do not readily break. Chains of two, three and four units are common; so are chains of twenty and more. The whole population in a juice is usually summarised by its mean degree of polymerisation, and that single number explains more about how a cider tastes than the total tannin figure ever will.
The reason is that bitterness and astringency are different phenomena with different size requirements. Bitterness is a taste: a molecule has to fit a receptor on the tongue, and only the smaller oligomers are small enough to do it well. Astringency is not a taste at all. It is what happens when a long, flexible polymer with many hydroxyl groups cross-links the proline-rich proteins in saliva and precipitates them, stripping away the film that normally lets the mouth slide against itself. The tongue reports roughness and drag. Short chains cannot cross-link enough protein to do this; long chains can, and the longer they are the better they do it, up to the point where they become too insoluble to stay in the drink at all.
So two ciders with identical total tannin can be entirely different propositions. One built on short oligomers is bitter and comparatively soft; one built on long polymers is drying and comparatively unbitter. This is why the Long Ashton classification, which measures total tannin, explicitly does not predict the balance of bitterness and astringency, and why cultivars with similar analytical figures have such different reputations among makers. It is also why the mouth-feel of a cider changes with time: procyanidins go on polymerising in the tank and the bottle, so bitterness recedes, astringency first rises and then falls as the longest chains drop out as sediment.
Everything a maker does between the mill and the bottle moves this. Procyanidins sit in the skin and flesh and, in high concentration, the seeds, so how finely the fruit is milled and how long the pomace macerates decides how much is extracted. Polyphenol oxidase attacks them in the presence of air, coupling them into larger, browner and less soluble structures — which is exactly why deliberately oxidised juice makes a softer, less bitter cider than sulphited juice from the same fruit. Protein fining works by mimicking saliva: gelatin or isinglass added to the tank precipitates the longest chains preferentially, taking astringency out and leaving bitterness comparatively untouched. And in the glass, the same protein binding happens with food, which is why a tannic cider reads quite differently alongside a hard cheese or a fatty pork dish than it does alone.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
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
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.
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.
Enzymes
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.
Phenolics
Tannin–protein complexes
What astringency physically is: long tannin chains cross-linking salivary proteins and precipitating them, which is also the mechanism behind fining, protein haze and the classic cider-and-cheese pairing.
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.
Aldehydes
Acrolein
A sharp aldehyde made by lactic bacteria from glycerol, which reacts with tannin to produce an intense, lingering bitterness in cider that was sound when it was bottled.
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.
- 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
- How do you blend 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.
- Why does my cider dry my mouth out — Astringency is tannin binding the proteins in saliva, which is felt as roughness rather than tasted. Too much comes from heavy pressing, long maceration, or fruit far higher in tannin than the blend can carry.
- Why does tannic cider feel drying rather than bitter — Because astringency is a physical event rather than a taste. Tannin cross-links the proteins that lubricate the mouth, and the loss of lubrication is what registers as drying; bitterness is a separate receptor event happening at the same time.
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.
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.
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.
A Somerset Pomona: The Cider Apples of Somerset
Liz Copas, The Dovecote Press, 2001. ISBN 9781874336877 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against Open Library: Liz Copas, The Dovecote Press, 2001, ISBN 9781874336877. The author was Long Ashton’s cider pomologist, which is why this work is registered for Somerset cultivar identity at all — it is the nearest thing to a successor to the station’s own descriptions. No copy was opened. Not digitised in any open collection.
Impact of apple procyanidins on sensory perception in model cider (parts 1 and 2)
Symoneaux, Baron, Marnet, Bauduin and Chollet, LWT — Food Science and Technology 57:22–27; and Symoneaux, Chollet, Bauduin, Le Quéré and Baron, LWT 57:28–34 · peer-reviewed literature · retrieved 2026-08-24
A pair of companion papers that do the one experiment the tannin question needs: hold the acid, the sugar and the alcohol constant, vary only the procyanidin fraction, and ask a panel what changed. They are the reason CiderHQ can say that bitterness and astringency separate on chain length rather than on quantity, and that they do not separate the same way at every concentration. Both abstracts and both bibliographic records verified on 2026-08-24; the full texts are on ScienceDirect behind a paywall and were not opened. Part 2 is doi:10.1016/j.lwt.2014.01.007.