Glossary · Microbiology
Vinegar fly
Also written fruit fly, Drosophila. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
The small fly, chiefly Drosophila melanogaster, that breeds on fermenting fruit and carries acetic acid bacteria and spoilage yeasts on its body from pomace heap to open vessel.
- Subject
- Microbiology
- Also written
- fruit fly, Drosophila
In more detail
Fly control is a legitimate microbiological control in a cider house: screening open vessels, keeping pomace away from the building, cleaning spills, and fitting airlocks addresses a real vector rather than a nuisance.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Microbiology
Acetic acid bacteria
Aerobic bacteria — *Acetobacter*, *Gluconobacter* and *Komagataeibacter* — that oxidise ethanol to acetic acid. They require oxygen, which is why they colonise surfaces, ullage and slack fittings.
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.
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.
Fermentation
Airlock
A water-sealed valve fitted to a fermenting vessel that lets carbon dioxide escape while preventing air, insects and airborne organisms from entering.
Milling and pressing
Pomace
Milled fruit — flesh, skin, pips and stalk fragments — before pressing, and the spent solids left in the press afterwards. Both senses are in everyday use and context distinguishes them.
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.
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.