Glossary · Chemistry
Dissolved oxygen
Also written DO. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
Oxygen carried in solution. Useful to yeast at the start of fermentation, and damaging afterwards, when it drives oxidation, acetification and the loss of aroma.
- Subject
- Chemistry
- Also written
- DO
In more detail
Every transfer picks up oxygen — racking, filtration, bottling — so cellar practice after fermentation is largely about minimising it: full vessels, tight fittings, gentle pumping and inert gas where it is available. A tannic cider tolerates more oxygen than a light one, because its phenolics consume it.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Chemistry
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.
Production
Oxygen management in fermentation
Giving the yeast the oxygen it needs early to build viable membranes, then excluding it once fermentation is under way and especially once it slows.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Faults
Oxidation
The chemical damage done by oxygen to a finished cider: loss of fresh fruit aroma, browning, and the arrival of acetaldehyde, nutty and sherry-like notes.
Fermentation
Ullage
The empty space between the surface of the cider and the top of its container, and by extension the volume lost that creates it. Ullage in a maturing cask is where oxidation and acetification start.
Faults
Acetification
The oxidation of ethanol to acetic acid by acetic acid bacteria, turning cider progressively into vinegar. It requires oxygen and is the classic fault of a slack, part-empty cask.
Fermentation
Racking
Transferring cider off its sediment into a clean vessel, leaving the lees behind. It is the basic maintenance operation of the cellar and the traditional method of slowing a fermentation.
Chemistry
Polyphenol
The broad class of plant compounds carrying multiple phenol rings. In apples this includes procyanidins, hydroxycinnamic acids such as chlorogenic acid, flavonols, dihydrochalcones such as phloridzin, and anthocyanins in red-fleshed fruit.
Where to go next
- Cider glossary — The whole vocabulary, by subject and A–Z.
- Comparisons — Terms that are only really clear when set against the thing they are not.
- Search — Finds terms by their aliases and by their spellings in other languages.
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.
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.