Compound
Ammonium nitrogen
The nitrogen form yeast takes up fastest and the one most nutrient additions supply, useful for rescuing a ferment and a poor substitute for a properly balanced juice.
Also called Ammonium, DAP, Diammonium phosphate.
- Class
- Nitrogen compounds
- Formula
- Not a single molecule — see below
- How often it matters
- Regularly encountered
What it does in cider
- Is assimilated preferentially and rapidly, so an addition produces a visible change in fermentation rate within a day.
- Represents only a small fraction of the natural assimilable nitrogen in apple juice, most of which is amino acids.
- Suppresses the Ehrlich pathway when abundant, since yeast supplied with ammonium has no need to strip nitrogen from amino acids.
- Supplies nitrogen without the vitamins, sterols and survival factors that complex nutrients provide, so it does not address every deficiency a cider ferment can have.
Measured figures
Shown as they were measured, with the context each was taken in. They are not averaged: a concentration recorded in one country's fruit in one decade is not a constant.
Ammonium nitrogen8.0–9.0 mg/L
Virginia, United States, 2014–2015 · 108 samples · Enzymatic ammonia assay (Ammonia-Rapid) · Boudreau, Peck, O’Keefe and Stewart, Food Science & Nutrition 6(1):119–123
Recorded as a range because the paper itself gives two figures: the abstract says 9 mg N/L and the results section says 8 ± 1 mg/L, which is rounding rather than disagreement. Either way it is about a seventh of the assimilable nitrogen, and it did not correlate with the total — which is why the fraction yeast reaches for first is also the fraction an apple juice is least likely to have.
The inorganic fraction of assimilable nitrogen, taken up first and exhausted first. Measured in milligrams per litre.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
Nutrient addition
Supplementing a characteristically nitrogen-poor juice so that yeast can complete fermentation without producing sulphide or stalling.
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.
Restarting a stuck fermentation
Diagnosing why a ferment has stopped with sugar remaining, then building an acclimatised starter and stepping the cider into it rather than pitching yeast into the problem.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
Wild fermentation
Letting the microflora already present on the fruit and in the press house carry the ferment, in a succession rather than as a single organism.
Inoculated fermentation
Starting a ferment by pitching a chosen yeast culture so that one known strain, rather than the fruit’s resident population, does the work.
Keeving
Forming a floating pectin gel that lifts nutrients and solids out of the juice, so that the ferment starves before it finishes and leaves natural sweetness behind.
Faults it is implicated in
Being implicated is not the same as being a fault. Several of the compounds on this site are ordinary constituents of a sound cider and define a named fault only above a concentration.
Stuck fermentation
A fermentation that has stopped before the sugar is gone and will not restart, leaving a sweet, low-alcohol cider that is vulnerable to everything.
Sluggish fermentation
A fermentation that is still moving but far more slowly than it should, extending the period during which the cider is weak, sweet and exposed.
Hydrogen sulphide
A rotten-egg or drain smell from hydrogen sulphide produced by stressed yeast, usually the first visible consequence of a nitrogen-short juice.
Nitrogen deficiency character
The set of characters a nitrogen-starved fermentation produces together — sulphide, a stalled or dragging ferment, harsh higher alcohols and a thin, hard cider.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
Described in full
- Shape
- A grouped bar chart. Three groups along the bottom are the three diammonium phosphate treatments — low at 22.3, intermediate at 144.3 and high at 369.3 milligrams per litre, all added to one juice that already carried 63.7 milligrams of assimilable nitrogen per litre. Each group holds two bars, one per yeast strain, and each bar is labelled with its value.
- Strain UCD522
- Low 123.75, intermediate 288.25, high 44.125 micrograms of hydrogen sulphide per 100 millilitres. The intermediate treatment produced twice what the low one did and more than six times what the high one did.
- Strain UCD932
- Zero at all three treatments. No hydrogen sulphide was detected from this strain regardless of how much nitrogen it was given, so its three bars are drawn as a flat line at the axis and labelled “none detected”.
- The threshold line
- A dashed horizontal reference is not drawn, because the sensory threshold — about 0.41 micrograms per litre — is roughly a thousandth of the smallest bar here and would sit indistinguishably on the axis. That is the point worth taking away: every one of these fermentations was far above the concentration a nose can find.
- What it corrects
- The common rule is that low nitrogen causes sulphide and adding nutrient cures it. On these data, adding some nutrient was worse than adding none, and adding a lot was better than either — but only for the strain that made sulphide at all. Strain choice came before nitrogen.
- Scope
- One juice, one temperature — 20 degrees Celsius — one pitching rate, two strains, three treatments, in triplicate. The shape of the relationship is the finding; the numbers belong to this experiment.
About Ammonium nitrogen
Ammonium is the simplest nitrogen source a yeast can have, requiring no deamination and no transport machinery beyond a dedicated permease, and yeast takes it up in preference to amino acids. That is what makes diammonium phosphate the standard fermentation nutrient: it is cheap, it is unambiguous, and its effect on a sluggish ferment is quick enough to be visible.
It is also what makes it a partial answer. A cider juice deficient in assimilable nitrogen is usually deficient in other things too — thiamine most commonly, and the sterols and unsaturated fatty acids a yeast needs for membrane integrity. Ammonium supplies none of these, so a ferment fed ammonium alone can pick up speed and still finish badly. Complex nutrient preparations, based on inactivated yeast, supply the rest, which is why most modern practice uses a combination.
Timing matters more than quantity. Nitrogen added at pitching builds population; nitrogen added around a third of the way through sugar depletion supports the cells that already exist through the difficult end of the ferment. A single large early addition is used inefficiently, drives excess biomass and heat, and leaves residual nitrogen in the finished cider for spoilage organisms to find. There is a further reason for restraint: yeast excretes urea when nitrogen is abundant, and urea reacts with ethanol to form ethyl carbamate.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Nitrogen compounds
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.
Nitrogen compounds
Amino acids
The largest usable nitrogen fraction in apple juice, and the raw material from which yeast builds both its own protein and most of the aroma compounds a cider carries.
Nitrogen compounds
Thiamine
A vitamin yeast cannot ferment without, frequently limiting in cider juice, and destroyed by the sulphite added to protect that juice.
Alcohols
Higher alcohols
The group of larger alcohols yeast makes from amino acids, welcome as background complexity in trace and harsh and solvent-like in quantity.
Nitrogen compounds
Ethyl carbamate
A trace contaminant formed when urea reacts with ethanol, present at low levels in fermented drinks and a genuine concern in apple spirits rather than in cider.
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.
- Why did my cider stop fermenting — The usual causes are a shortage of yeast-available nitrogen, a temperature that has dropped, too much sulphite at the start, or a yeast that has reached its alcohol limit. Check the gravity before assuming anything is wrong: many ciders simply finish.
- Which yeast ferments cider — Saccharomyces cerevisiae finishes almost every cider fermentation, whether it was pitched or arrived from the press house. In a spontaneous ferment it is not the first organism present, only the one that survives the alcohol it makes.
- How do i get rid of the sulphur smell in my cider — Racking with a little splashing usually blows off free hydrogen sulphide while it is still fresh. Once it has reacted into mercaptans the smell becomes rubbery and no longer responds to aeration.
- What does a nitrogen-starved cider taste like
- What is yan and why does cider juice run short of it — Yeast assimilable nitrogen is the nitrogen yeast can actually use. Apple juice is usually short of it — in one Virginia survey of 108 samples, 94 per cent fell below the level wine practice treats as a minimum — which is why cider ferments stall more readily than wine ferments.
- Why is my cider fermenting so slowly
Where to go next
- All compounds — Grouped by what the fruit brings and what the ferment makes of it.
- Sensory — Every descriptor, with the compound or process that causes it.
- Microbiology — The organisms whose metabolism most of this chemistry belongs to.
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.
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.
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.