Glossary · Fermentation
Yeast nutrient
Also written nutrient addition, DAP. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
Nitrogen and micronutrients added to a must that cannot supply the yeast’s needs. Diammonium phosphate provides inorganic nitrogen; complex nutrients also supply amino acids, vitamins and sterols.
- Subject
- Fermentation
- Also written
- nutrient addition, DAP
In more detail
Apple juice is often low in assimilable nitrogen — far lower than grape must — and low-nitrogen ferments are slow, stall readily and produce hydrogen sulphide. Nutrient is therefore a common addition, timed early or at about a third of the way through the ferment so the yeast can use it.
It is also a choice with consequences: a nitrogen-rich ferment runs fast and clean but will not keeve, and over-addition leaves residual nitrogen for spoilage organisms.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Production
Yeast nutrition
What a fermenting yeast population actually needs from apple juice — assimilable nitrogen, vitamins and membrane lipids — and what goes wrong when the juice cannot supply it.
Chemistry
Yeast-assimilable nitrogen
The nitrogen a yeast can actually use, which apple juice is chronically short of — the shortage behind both stuck fermentations and rotten-egg aromas, and the shortage keeving deliberately makes worse.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Chemistry
YAN
The nitrogen a yeast can actually use — free amino nitrogen plus ammonium — expressed in milligrams of nitrogen per litre. Apple juice is frequently short of it.
Fermentation
Stuck fermentation
A fermentation that has halted before the sugar is used up and will not restart on its own. It is distinct from a deliberately arrested ferment and from a merely sluggish one.
Chemistry
Hydrogen sulphide
A volatile sulphur compound produced by stressed yeast, smelling of rotten eggs at very low concentrations. In cider it is usually a symptom of nitrogen deficiency during fermentation.
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.
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.
Cornell Cider Research and Extension programme
Cornell University, School of Integrative Plant Science · university · passage verified 2026-08-24
Runs cultivar trials in New York State and publishes juice chemistry for European cider varieties grown in a North American climate — the single most useful counterweight to treating English figures as universal.
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.