Compound
Ascorbic acid
An oxygen scavenger that protects colour and aroma while it lasts and can promote browning once it is exhausted, which is why it is never used without sulphur dioxide.
Also called Vitamin C, L-ascorbic acid.
- Class
- Additives and processing aids
- Formula
- C6H8O6
- How often it matters
- Occasional
What it does in cider
- Reacts with dissolved oxygen faster than most phenolics do, so it intercepts oxygen at bottling and preserves pale colour and fresh aroma.
- Produces hydrogen peroxide as it does so, which will oxidise ethanol to acetaldehyde unless sulphur dioxide is present to destroy it.
- Becomes pro-oxidant once consumed, because its own degradation products participate in browning reactions.
- Occurs naturally in apple juice at low and variable concentration, and is largely lost during pressing and fermentation.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
Bottling
Transferring finished cider into glass, where the dominant variable is how much oxygen the liquid picks up in the few seconds it takes to fill and close each bottle.
Juice storage
Holding unfermented juice sound between pressing and fermentation, by chilling, sulphiting, gas blanketing, freezing or aseptic filling.
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.
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.
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.
Pinking
An unexpected pink or salmon tint developing in a pale cider or perry, associated with oxidation of colourless phenolic precursors.
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.
Acetaldehyde excess
A bruised-apple, green-nut or sherry aroma from acetaldehyde, produced by oxidation, by film yeast, or left behind by a ferment that was interrupted.
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.
Atypical ageing
A cider that loses its fruit unusually early and develops a flat, faintly acrid or naphthalene-like character — a syndrome described in white wine and less firmly established in cider.
About Ascorbic acid
Ascorbic acid is a fast, sacrificial reducing agent. Add it to a cider at bottling and it takes the dissolved and headspace oxygen preferentially, sparing the phenolics that would otherwise oxidise and the aroma compounds that would otherwise be lost. For a pale, fruit-driven cider intended to be drunk young, this is a genuinely useful intervention.
The catch is stoichiometric. When ascorbic acid reduces oxygen it generates hydrogen peroxide, and hydrogen peroxide in an alcoholic solution oxidises ethanol to acetaldehyde — the flat, bruised-apple note the treatment was supposed to prevent. Sulphur dioxide destroys peroxide, so the two additions are a pair: ascorbic acid without adequate free SO2 can leave a cider worse than no addition at all.
The second catch is temporal. Ascorbic acid is consumed, and once it is gone its degradation products take part in non-enzymatic browning rather than preventing it. A cider protected this way is protected for a period rather than indefinitely, which makes it a tool for short-shelf-life products and a poor choice for anything intended to age.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Gases
Dissolved oxygen
Essential to a healthy yeast population at the start of fermentation and the principal enemy of a cider from the moment fermentation ends.
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.
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.
- 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 is oxidation in 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 acetaldehyde
- Why does my cider taste like sherry — Acetaldehyde, the compound that sits between alcohol and acetic acid, gives a bruised-apple and sherry-like character. It rises when cider is exposed to air or when a ferment is interrupted.
- How is cider bottled
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.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.