Glossary · Fermentation
Chapeau brun
French. Kept in its own language here rather than translated into the nearest English word, because the nearest English word is usually cut on a different axis.
Also written chapeau, brown cap. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
The brown gelatinous cap of pectate, solids and yeast that floats to the surface during keeving. Its formation is the visible test that keeving has worked.
- Subject
- Fermentation
- Language
- French
- Also written
- chapeau, brown cap
In more detail
A good cap is firm, continuous and brown, and sits above a layer of bright juice with a compact sediment below. A cap that never forms, or that breaks up and sinks, means the juice was too rich in nitrogen, too warm, or too poor in the enzyme and calcium the gel needs — and the batch is fermented conventionally instead.
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.
Fermentation
Keeving
A pre-fermentation clarification in which pectin in the juice is gelled into a floating brown cap, taking nutrients and yeast with it, so that the clear juice drawn from beneath ferments slowly and stops with sugar remaining.
Fermentation
Défécation
The French name for keeving, from the Latin for removing the dregs. It describes the same pectate-gel clarification and the same nutrient stripping that keeving does.
Chemistry
Pectin
A structural polysaccharide of fruit cell walls, released into juice during milling and pressing. It thickens juice, holds haze in suspension and is the raw material of the keeving cap.
Chemistry
Calcium pectate
The insoluble gel formed when calcium ions cross-link de-methylated pectin. It is the substance of the keeving cap, and the reason calcium salts are sometimes added to encourage one.
Equipment
Keeve
The open vessel in which juice is held while it forms its brown cap. The word is also used as a verb for the process itself, which took its name from the vessel.
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.
Institut Français des Productions Cidricoles (IFPC)
IFPC · research institute · retrieved 2026-08-24
The French technical institute for cider production. The authority for the French cultivar classification families, for keeving as an industrial process, and for the pectin and nitrogen chemistry that keeving depends on.
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.