Glossary · Microbiology
Brettanomyces
Also written Brett, Dekkera. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
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.
- Subject
- Microbiology
- Also written
- Brett, Dekkera
In more detail
Brett metabolises hydroxycinnamic acids into ethylphenols and ethylcatechols, and can also ferment residual sugars that Saccharomyces has left, so it is a spoilage risk in packaged sweet cider as well as an aromatic influence in cask. It tolerates alcohol and low levels of sulphite and grows extremely slowly, which is why it appears months after everything looked stable.
Whether Brett character is a fault is a question of degree and intent. Some traditional and barrel-aged ciders carry it as part of their identity; in a clean modern cider it is a defect, and in either case it is difficult to remove once established in wood.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
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.
Fault
Brettanomyces character
Farmyard, horse-blanket, smoky and sticking-plaster aromas from *Brettanomyces* yeast converting hydroxycinnamic acids into volatile phenols.
Chemistry
4-Ethylphenol
The horse-and-sticking-plaster compound, made by *Dekkera* from a phenolic acid the fruit supplied, and the clearest case in cider of one molecule being a tradition in one glass and a fault in another.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Sensory
Brett character
The aroma complex produced by *Brettanomyces*: farmyard, horse blanket, leather, clove and sticking plaster, from 4-ethylphenol, 4-ethylguaiacol and related compounds.
Sensory
Farmyard
A descriptor for the animal, stable-like aroma associated chiefly with *Brettanomyces* ethylphenols, and sometimes loosely applied to any rustic character in traditional cider.
Sensory
Sticking plaster
A descriptor for the sharp medicinal, antiseptic note of volatile phenols, most often from *Brettanomyces* and occasionally from chlorophenol contamination in packaging or premises.
Fermentation
Barrel ageing
Maturing cider in wood, either in neutral casks used purely as vessels or in barrels chosen to contribute oak, spirit or wine character.
Chemistry
Chlorogenic acid
The most abundant hydroxycinnamic acid in apple juice, and the principal substrate for enzymatic browning. It is also a precursor of the ethylphenols that *Brettanomyces* produces.
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.
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.
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.