Compound
Phloridzin
A dihydrochalcone found in apple and essentially nowhere else, which makes it both a contributor to bitterness and the standard chemical proof that a juice is apple juice.
Also called Phlorizin, Phloretin-2′-glucoside.
- Class
- Phenolics
- Formula
- C21H24O10
- How often it matters
- Occasional
What it does in cider
- Occurs in Malus and in very few other genera, so its presence identifies apple material and its absence in a pear juice is equally diagnostic.
- Contributes bitterness in its own right, adding to the bitterness of the small procyanidins.
- Concentrates heavily in seeds, leaves and bark rather than flesh, so juice concentration depends on how hard the mill treated the pips.
- Oxidises to reactive products that participate in browning, though more slowly than chlorogenic acid.
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.
- bitter
- apple pip
A genuine bitter contributor, though present at concentrations well below the procyanidins in most juices; its effect is additive rather than dominant.
Descriptors it is responsible for
Sensory records that name Phloridzin 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.
- Apple core — A faintly bitter, faintly almond-like note from crushed pips and core tissue passing through the mill with the flesh.
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. |
| Phenolic character | Smoky, spicy, leathery or medicinal aromas that sit apart from fruit. |
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
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 Phloridzin
Phloridzin is a dihydrochalcone — a flavonoid skeleton with the central ring opened — carrying a glucose unit. Its distribution in the plant kingdom is narrow enough to be useful: it is characteristic of Malus, and juice authenticity work uses it as an apple marker in much the way other markers are used for citrus. A pear juice does not contain it, which is one of the ways an apple-and-pear blend can be distinguished from a straight perry.
In the fruit it is concentrated in the seeds, in leaf and in bark rather than in the flesh, so how much reaches the juice is largely a question of milling. A mill that shatters pips liberates more of it, along with the other seed phenolics, and gives a measurably more bitter juice than one that leaves the cores intact.
It is a real bitter compound, and it belongs on the short list of things that make cider apples taste as they do alongside the procyanidins that get most of the attention. Its aglycone, phloretin, and its oxidation products take part in the browning chemistry of pressed juice, though more slowly than the hydroxycinnamic acids.
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
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
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.
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.
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.
- 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.
- Why is my cider so bitter
- 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.
- What is chlorogenic acid in apple juice — It is the most abundant hydroxycinnamic acid in apples and the main substrate for enzymatic browning, so it is largely responsible for how brown a pressed juice goes and how quickly.
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.
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.
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.