Compound
Galacturonic acid
The sugar acid that pectin chains are built from, released as they break down, and a significant part of why juice from rotten fruit binds so much of the sulphite added to it.
Also called D-galacturonic acid.
- Class
- Acids
- Formula
- C6H10O7
- How often it matters
- Occasional
What it does in cider
- Forms the backbone of pectin: the polymer is a chain of these units, some methyl-esterified, some free.
- Accumulates in juice as pectin is degraded, whether by an added pectinase or by mould enzymes acting on fruit in the orchard.
- Binds sulphur dioxide, so juice rich in it needs a larger sulphite addition to reach the same free SO2 — one of the concrete penalties of pressing rotten fruit.
- Contributes a small amount of non-volatile acidity that malolactic fermentation does not remove.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
Pectinase treatment
Adding pectin-degrading enzyme preparations to juice so that haze-forming and viscosity-forming pectin is broken down before fermentation.
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.
Enzyme addition to pomace
Dosing pectin-degrading enzyme into milled pomace rather than into juice, to raise press yield and change how the cake drains.
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.
Excess sulphur dioxide
A struck-match or burnt-match aroma and a prickle at the back of the nose from too much free sulphur dioxide, with a real health consideration for sulphite-sensitive people.
Mould taint
Musty, earthy, cellar-damp or rotten-fruit character carried in from mouldy fruit or from mouldy equipment, and a marker that the patulin question needs asking.
Pectin haze
A persistent, slightly viscous haze that will not settle, caused by pectin from the fruit remaining in solution as a colloid.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
Botrytis cinerea
Grey mould: a broad-host-range fruit rot whose laccase enzyme oxidises phenolics and whose glucans make a juice difficult to clarify.
Penicillium expansum
The blue mould of stored apples and the principal producer of patulin, the one genuine chemical safety issue that rotten cider fruit raises.
Monilinia fructigena
The brown rot of apples and pears, recognisable by concentric rings of buff pustules, and a major cause of fruit loss between the orchard and the mill.
Gluconobacter oxydans
A sugar-preferring acetic acid bacterium abundant on damaged fruit and in fresh juice, which oxidises glucose to gluconic acid before fermentation begins.
About Galacturonic acid
Take a pectin chain apart and what remains is galacturonic acid, a six-carbon sugar oxidised at one end to a carboxylic acid. It is present in juice both as free acid and as the polymer, and the ratio between the two is a running record of how much pectin degradation has occurred — through ripening, through mould attack in the orchard, or through a pectinase addition in the tank.
Its practical significance is a sulphite one. Sulphur dioxide added to juice does not stay free; a proportion binds reversibly to carbonyl compounds, and bound SO2 has no antimicrobial effect whatever. Galacturonic acid and its oxidation products are among the binders, alongside acetaldehyde and the ketonic compounds that moulds generate. Juice pressed from sound fruit binds relatively little. Juice pressed from fruit that has been sitting under trees in a wet autumn binds a great deal, and a maker who doses to a standard rate finds that the free SO2 measured a day later is a fraction of what was added.
The lesson runs the other way round from how sulphiting is usually discussed. The question is not how much sulphite to add but how much binding capacity the juice contains, and the honest answer to a heavily bound juice is better fruit sorting rather than a larger addition — because the sulphite consumed by binding does no work and the bound fraction is still counted in any legal total.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Polysaccharides
Pectin
The structural polysaccharide of fruit cell walls, which decides how much juice a press releases, whether a cider ever clears, and whether keeving is possible at all.
Enzymes
Pectin lyase
The chain-cutting activity in a commercial pectinase preparation, which raises press yield and clears a juice by destroying the colloid pectin creates — and destroys the possibility of keeving in the same stroke.
Enzymes
Pectin methylesterase
The enzyme that strips methyl groups from pectin, exposing the charged sites that calcium bridges — which is the reaction the whole of keeving is built on.
Additives and processing aids
Sulphur dioxide
The antimicrobial and antioxidant on which most modern cidermaking depends, and whose effectiveness collapses as pH rises — which makes every sulphiting decision a pH decision first.
Aldehydes
Acetaldehyde
The compound sitting one step short of ethanol, which smells of bruised apple and sherry, binds most of the sulphite added to a cider, and is the chemical signature of oxidation.
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.
- Does cider contain sulphites — Most does. Sulphur dioxide is added to protect juice and finished cider, and fermentation itself produces a small amount even when none is added. European labels must declare it above 10 mg per litre.
- What does pectin do in cider — Pectin is the structural polysaccharide that holds fruit cells together. In juice it holds haze in suspension, and it is the molecule keeving depends on: strip its methyl groups and it will gel with calcium and float the nutrients out of the juice.
- Can i drink cider if i react to sulphites — Sulphite sensitivity is real but uncommon, and is most often reported in people with asthma. CiderHQ cannot give medical advice; what it can say is that ciders made without added sulphite exist and are labelled as such.
- What is acetaldehyde
- Why does mouldy fruit matter for cider — Penicillium expansum is the blue mould of stored apples and the principal producer of patulin. Sorting rotten fruit out before milling is a food-safety step and not only a quality one.
- 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.
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.
Hochschule Geisenheim University — beverage technology
Hochschule Geisenheim · university · retrieved 2026-08-24
German beverage-technology research covering apple wine and fruit juice processing, including the enzymology of clarification.
Institut Français des Productions Cidricoles (IFPC)
IFPC · research institute · retrieved 2026-08-24
The French technical institute for cider production. The authority for the French cultivar classification families, for keeving as an industrial process, and for the pectin and nitrogen chemistry that keeving depends on.