Compound
Quercetin glycosides
The yellow flavonols of apple skin, made in response to sunlight, which contribute a fine astringency and reach the juice only in proportion to how much skin was pressed.
Also called Flavonols, Rutin and related glycosides.
- Class
- Phenolics
- Formula
- Not a single molecule — see below
- How often it matters
- Specialist — met in particular circumstances
What it does in cider
- Accumulates almost exclusively in the skin, where the compounds screen ultraviolet light, so sun-exposed fruit carries far more than shaded fruit.
- Contributes a fine-grained astringency and a trace of bitterness distinct from the grip of procyanidins.
- Adds yellow tone to juice and cider colour.
- Reaches juice only in the proportion that skin contributes, making it a marker of milling severity and maceration rather than of cultivar alone.
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.
- fine astringency
- faint bitterness
Descriptors it is responsible for
Sensory records that name Quercetin glycosides as a cause. Each states the perception and the mechanism behind it.
- Apple skin — The dry, faintly waxy and slightly bitter aroma of the fruit’s surface rather than its flesh, carried by cuticular waxes, hexyl esters and skin-concentrated phenolics.
- Citrus pith — A dry, bitter citrus note where phenolic bitterness sits alongside sharp acidity rather than behind fruit.
The structure it moves
| Dimension | What it is |
|---|---|
| Astringency | The drying, rough sensation left after swallowing. |
| Bitterness | A taste sensed at the back of the tongue, distinct from the drying grip of astringency. |
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
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.
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.
Orchard floor management
What is grown, mown, grazed or suppressed beneath and between the trees, which affects tree vigour, juice nitrogen, harvest logistics and the biological interest of the ground.
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.
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.
About Quercetin glycosides
Flavonols in apple are almost entirely a skin phenomenon and almost entirely a light phenomenon. The tree makes them where ultraviolet radiation falls, as a sunscreen, so fruit on the outside of a canopy carries several times what fruit on the inside carries, and the same cultivar picked from a standard orchard and from a dense bush orchard analyses differently.
Because they are in the skin, how much ends up in the juice is a processing question. A gentle press of coarsely milled fruit extracts little; a hard press of finely milled pomace after a long maceration extracts a good deal more, along with everything else the skin holds.
They contribute a fine, slightly dusty astringency that trained panels distinguish from procyanidin astringency, and they add yellow to the colour. Neither effect is large, but both are among the small differences that make a whole-fruit cider taste different from one made from clarified juice.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
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.
Phenolics
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Phenolics
Anthocyanins
The red pigments of apple skin and red-fleshed cultivars, which are colour rather than flavour and which fade quickly in a cider unless the pH is low.
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.
- Do i need a filter to make cider
- 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.
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.