Comparison
Brett as character vs Brett as fault
Is Brett in cider a fault?
In short
Brettanomyces, or Dekkera, converts hydroxycinnamic acids in the cider into volatile phenols — principally 4-ethylphenol and 4-ethylguaiacol. At low concentration these read as spice, leather, smoke and farmyard, and they are part of the character of a good deal of traditional cask cider and of many barrel-aged ciders.
At higher concentration the same compounds read as sticking plaster, medicinal and horse-like, and they mask the fruit entirely. The individual threshold varies a great deal between tasters, which is why one drinker’s complexity is another’s defect on the same glass.
The reason producers treat it seriously is not the aroma but the persistence. Brettanomyces tolerates alcohol and sulphite well, ferments sugars that Saccharomyces leaves behind, and survives in wooden vessels that cannot be fully sterilised. A cider showing Brett in the bottle is usually still changing, so the level found today is not the level found in a year.
The two things being compared
Each side described in its own terms first, so the table below has something to hang on.
Brett as character
Low levels of volatile phenols contributing spice, leather and farmyard notes that sit within the cider rather than over it.
Brett as fault
Volatile phenols above threshold, giving sticking-plaster and medicinal character that masks the fruit — and generally still increasing.
Where they differ
Dimension by dimension. Where a row needs a qualification, it carries one rather than being simplified until it fits.
| Dimension | Brett as character | Brett as fault |
|---|---|---|
| Compounds | 4-ethylphenol and 4-ethylguaiacol at low concentration. | The same compounds well above threshold. |
| Descriptors | Spice, leather, smoke, farmyard. | Sticking plaster, medicinal, horse, mousy in some cases. |
| Relationship to the fruit | Sits alongside it. | Masks it. |
| StabilityA stable low level is a character; an unstable one is a fault in waiting, whatever it tastes like today. | Only if the organism is no longer active. | Actively increasing, which is the defining problem. |
| Taster variationSensitivity to 4-ethylphenol varies widely between individuals, so disagreement is genuine rather than a matter of expertise. | Perceived as complexity by some. | Perceived as a defect by others at the same level. |
| Where it comes from | Wooden vessels and cellar flora that cannot be sterilised out. | The same source; the difference is population and time. |
| Control | Vessel management, sulphite and temperature keep it in check. | Sterile filtration or pasteurisation are the reliable options once it is established. |
Notes under a dimension name qualify the whole row, not one column.
When Brett as character is the relevant one
The circumstances in which this is the thing being described, rather than a reason to prefer it.
- The phenolic note is low, integrated and stable.
- You are describing a cask or barrel-aged cider whose tradition includes it.
When Brett as fault is the relevant one
The circumstances in which this is the thing being described, rather than a reason to prefer it.
- The phenolic note dominates or is medicinal.
- The cider is changing in the bottle and the character is increasing.
A misconception worth clearing up
This comparison exists partly because of the claim below, which is repeated often enough that most readers arrive holding it.
Brett is either a fault or a feature, and cider people simply disagree about which.
What is actually the case: Both are true of different levels of the same organism, and the more useful question is whether it is still active. A stable trace is a character; an active population in a sealed bottle will keep producing phenols until the substrate runs out, and where it ends up is not under anyone’s control.
Related comparisons
Distinctions that turn on the same thing, or that this one is routinely confused with.
Fault vs style feature
Many of the compounds recorded as faults are present in well-regarded traditional ciders. What separates a fault from a feature is concentration, integration and whether the producer intended and controlled it.
Barrel-aged vs tank-aged
Wood admits a slow trickle of oxygen and can contribute its own compounds; stainless steel admits neither, so it holds a cider as it was while wood changes it.
Oxidation as fault vs oxidation as style
Controlled slow oxidation during maturation develops colour, softens tannin and adds complexity; uncontrolled oxidation strips fruit aroma, browns the cider and pushes it towards acetaldehyde and vinegar.
Filtered vs unfiltered
Filtration removes suspended solids and, at fine enough grades, the organisms too; leaving it out keeps whatever is in suspension, including material that carries aroma and texture.
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.
- Is unfiltered cider better than filtered — Neither is better as such. Filtration removes yeast, haze and some flavour compounds and makes a cider stable; leaving it unfiltered keeps more texture and aroma and leaves the cider alive in the bottle.
- When is a cider faulty and when is it just traditional — The same compound can be either, and the deciding factor is the tradition the cider belongs to and the concentration. Volatile acidity that would condemn a modern fresh-fruit cider is expected in a traditional Asturian one, and neither judgement is wrong.
- What does ageing cider in a barrel actually do
- When is oxidation in cider a fault
Where to go next
- All comparisons — The rest of the pairs, grouped by what kind of difference is at stake.
- Glossary — Either term on its own, defined without a second thing to hold it against.
- Learn about cider — The background these pages assume, written from the beginning.
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.
Peer-reviewed literature on apple phenolics and cider sensory perception
Various journals · peer-reviewed literature · registered as competent for this subject
Registered as a class rather than as one paper, because the mechanisms CiderHQ describes — tannin chain length driving the split between bitterness and astringency, salivary protein precipitation, enzymatic browning — are established across many studies rather than resting on any single one. Individual papers are cited where a specific number is quoted.