Glossary · Sensory
Mousiness
Also written mousy taint, mouse taint. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
A taint perceived only after swallowing, as a lingering flavour of mouse cage, stale popcorn or cracker, produced by tetrahydropyridines from lactic acid bacteria and Brettanomyces.
- Subject
- Sensory
- Also written
- mousy taint, mouse taint
In more detail
Mousiness is invisible on the nose because the responsible compounds are non-volatile at cider pH. Raising the pH releases them, which is why the diagnostic test is to rub a little cider on the back of the hand or hold it in the mouth: saliva does the neutralising and the taint appears seconds later.
A significant proportion of tasters cannot perceive it at all, so a panel can split completely on the same sample. It is favoured by high pH, low sulphite and the presence of residual sugar or lysine, and it does not fade with time in bottle.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Fault
Mousiness
A retronasal taint of mouse cage, stale popcorn or crackers that appears only after swallowing — and that a substantial fraction of people cannot detect at all.
Chemistry
Tetrahydropyridines
The compounds behind mousiness, which cannot be smelled in the glass because they are not volatile at cider pH and appear only as an aftertaste once saliva has raised the pH in the mouth.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Microbiology
Lactic acid bacteria
The bacteria that convert malic acid to lactic acid and, in other conditions, produce the disorders of ropiness, mousiness and acrolein bitterness. *Oenococcus*, *Lactiplantibacillus* and *Lactobacillus* species dominate in cider.
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.
Chemistry
pH
A logarithmic measure of hydrogen ion activity, and in cider the single most important number for microbial safety. Apple juice usually falls between pH 3.2 and 3.9.
Sensory
Aroma threshold
The lowest concentration at which a compound can be detected in a given medium, usually defined as the level at which half a panel distinguishes it from a blank.
Fermentation
Sulphiting
Adding sulphur dioxide, usually as potassium or sodium metabisulphite, to juice or cider to suppress spoilage organisms, inhibit oxidation and enzymatic browning, and give a selected yeast a clear field.
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.