Glossary · Fermentation
Barrel ageing
Also written cask ageing, wood ageing. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
Maturing cider in wood, either in neutral casks used purely as vessels or in barrels chosen to contribute oak, spirit or wine character.
- Subject
- Fermentation
- Also written
- cask ageing, wood ageing
In more detail
Traditional cider casks were old, large and neutral: their function was to hold the cider and admit a little oxygen, not to flavour it. Deliberate flavour extraction from new or spirit-seasoned oak is a modern practice, and brings vanillin, oak lactones and, in charred barrels, toast and smoke.
Wood is also a microbiological decision. Its porous surface harbours Brettanomyces, lactic bacteria and acetic bacteria that cannot be removed by cleaning, which is both the source of a cellar’s house character and the reason a single infected cask can spoil successive batches.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Production
Barrel ageing
Holding cider in wood — which may mean an old neutral vat used simply as a vessel, or fresh or spirit-seasoned oak used as a source of flavour, and the two are not the same operation.
Style
Barrel-aged cider
Cider matured in wood, where slow oxygen ingress, extraction from the staves and the barrel’s resident microflora all change the finished drink.
Microbiology
Dekkera bruxellensis
The yeast behind 4-ethylphenol, and the organism that a cider tradition may regard as its signature or its ruin depending on where and how it is made.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Fermentation
Maturation
The period after fermentation in which a cider settles, clarifies and changes chemically — esters forming and hydrolysing, phenolics polymerising, harsh notes integrating — before it is packaged or drunk.
Equipment
Cask
A wooden vessel of staves bound by hoops, bulging at the middle so it can be rolled and turned. Casks both store cider and shape it, admitting a slow ingress of oxygen through the wood.
Microbiology
Brettanomyces
A genus of slow-growing yeasts, *Dekkera* in its sexual form, that survive in wood and in finished cider and produce volatile phenols smelling of farmyard, leather, spice and sticking plaster.
Sensory
Oxidative
Showing the character that oxygen exposure brings — bruised apple, nuts, dried fruit, sherry and toffee — with fresh fruit aromas diminished. It may be a fault or a deliberate style.
Milling and pressing
Sanitation
The routine cleaning and disinfection of everything juice touches. In a cider house it is the single most effective control on spoilage, and it is separated into cleaning, which removes soil, and sanitising, which reduces the organisms left behind.
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.
Peer-reviewed literature on cider fermentation microbiology
Various journals · peer-reviewed literature · registered as competent for this subject
Covers the microbial succession of spontaneous cider fermentation, the role of non-Saccharomyces yeasts in the early stages, malolactic conversion by Oenococcus and Lactobacillus species, and the organisms behind the principal spoilage faults.