Juice treatment
Nutrient addition
Supplementing a characteristically nitrogen-poor juice so that yeast can complete fermentation without producing sulphide or stalling.
Also called Feeding the juice, Yeast nutrient supplementation, DAP addition.
- Stage
- Juice treatment
- Traditional in
- No single tradition — used wherever it suits
- What it most changes
- Fermentation character and Fruit character
- Safety
- None recorded
What it is
Apple juice is a poor growth medium for yeast in one specific respect: it carries substantially less assimilable nitrogen than grape must, and in some cultivars and some seasons far less. Nutrient addition is the deliberate supplementation of that shortfall, most often with an inorganic ammonium salt, an organic preparation derived from inactivated yeast, or a blended product containing both plus vitamins and micronutrients. It is a fermentation-management decision taken at the juice stage, and it is one of the few places in cider making where a small intervention reliably prevents a large and otherwise irreversible problem.
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.
Why it is used
- Deprived of assimilable nitrogen, yeast turns to the sulphur-bearing amino acids it can find and liberates hydrogen sulphide as it does so, producing a rotten-egg character that is far easier to prevent than to remove.
- Insufficient nitrogen limits the yeast population that can be built during the growth phase, and a small population fermenting a full sugar load is the commonest route to a sluggish or stuck ferment.
- Thiamine deficiency, which apple juice is also prone to, impairs the decarboxylation steps of yeast metabolism and can leave residual pyruvate and elevated acetaldehyde in the finished cider.
- Where juice has been clarified, centrifuged or keeved, the nitrogen that would have come from suspended solids has already been removed, so the shortfall is deeper than the fruit alone would suggest.
How it works
- Yeast assimilable nitrogen is the sum of two fractions: ammonium nitrogen, which yeast takes up directly, and alpha-amino nitrogen from free amino acids, of which proline is notably excluded because Saccharomyces cerevisiae cannot use it anaerobically.
- Diammonium phosphate supplies only the inorganic fraction. It raises the number but does not supply amino acids, sterols, unsaturated fatty acids or vitamins, so a juice fed only with DAP can still be functionally deficient.
- Organic nutrients derived from inactivated yeast supply amino nitrogen along with survival factors — sterols and unsaturated fatty acids — that support membrane integrity as ethanol rises, which is why they matter more late in fermentation than early.
- Timing changes the outcome: nitrogen supplied during the growth phase builds cell numbers, whereas nitrogen supplied around the middle of fermentation supports the existing population’s transport systems without producing another growth surge.
- Excess nitrogen accelerates the ferment and shifts amino acid metabolism towards the Ehrlich pathway, raising higher alcohols; it also leaves residual nitrogen that later feeds spoilage organisms and contributes to ethyl carbamate precursors.
What it changes
The direction this step pushes the finished drink in, dimension by dimension. A direction, not a measurement: how far it moves depends on the juice, the temperature and how the step is carried out.
| Dimension | Direction | Why |
|---|---|---|
| Fermentation character | Either way | Adequate nitrogen suppresses sulphide formation, but a surplus drives the Ehrlich pathway towards fusel alcohols, so the direction of the sensory change depends entirely on where the juice sat to begin with. |
| Fruit character | Either way | A ferment that runs too fast on excess nitrogen strips volatile esters out with the escaping carbon dioxide, while a nitrogen-starved ferment produces sulphidic notes that mask fruit; both directions lose aroma by different routes. |
The chemistry and the organisms
What is actually being changed, and by what. Each entry says what that compound or organism does in cider generally; this page is one place it does it.
Compounds involved
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.
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.
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.
Thiamine
A vitamin yeast cannot ferment without, frequently limiting in cider juice, and destroyed by the sulphite added to protect that juice.
Hydrogen sulphide
The rotten-egg gas a nitrogen-starved yeast produces, detectable at concentrations too small to measure easily, and removable only if it is caught before it becomes something worse.
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.
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 it is done with
Drawing a sample without spoiling the batch
Every sample is a small hole made in the protection around a batch: something goes in, air goes in with it, and cider comes out — so the technique is about drawing a representative sample while putting nothing back and letting in as little air as possible.
Laboratory measurement versus practical measurement
Gravity, temperature, pH and total acidity are all within reach of a careful person with modest equipment; alcohol by volume, sulphur dioxide for a declaration, patulin, methanol and microbiological counts are not, and pretending otherwise is how numbers on labels become wrong.
What can go wrong
Faults that begin at this step, or that this step makes more likely. Each one is set out with its causes and whether it can be put right.
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.
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.
Styles it produces
Categories in which this step is characteristic or required. Some name it in their definition; for others it is simply how they have always been made.
Recorded figures
Shown with the place, period and method each was taken under, and never averaged: the same step run in another cellar genuinely gives a different number.
Assimilable nitrogen22.3–369.3 mg/L
Ithaca, New York, United States, 2016 · Diammonium phosphate added at three rates — 22.3, 144.3 and 369.3 mg/L — to one juice of 63.7 mg N/L · Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264
These are addition rates of the salt, not of nitrogen, and they are the three points of a designed experiment rather than a dosing recommendation. What makes them worth recording is the result: the middle rate produced the most hydrogen sulphide of the three, twice the low rate and six times the high, so adding some nutrient was worse than adding none or adding plenty.
The nitrogen yeast can actually use. Cider juice is often short of it, which is why ferments stall. Measured in milligrams per litre.
More on nutrient addition
The nitrogen problem in cider is structural rather than incidental. Apples accumulate sugar and acid and comparatively little protein or free amino acid, and orchard nitrogen management — often deliberately restrained to control vegetative growth and improve fruit quality — pushes it lower still. Bittersweet cultivars are generally poorer than dessert fruit, and any juice that has been keeved, centrifuged or hard-fined has had a further slice taken out of it. The result is that a juice can be perfectly sound, correctly sulphited and correctly pitched, and still be incapable of supporting the ferment it has been asked to carry.
What matters is not nitrogen in general but the assimilable fraction. Yeast takes up ammonium directly and free amino acids through specific permeases, and proline — often a substantial share of the total amino acid pool — is unavailable under fermentation conditions. Diammonium phosphate addresses only the ammonium side of that ledger. It is cheap, effective at what it does, and incomplete: it supplies no amino acids, no sterols, no unsaturated fatty acids and no vitamins. Thiamine deserves separate mention because apple juice is often short of it and because sulphiting binds some of what is present; thiamine-deficient yeast leaves elevated acetaldehyde and pyruvate behind, which reads as a hard, slightly green cider rather than as an obvious fault.
Practice differs sharply by tradition and by intention. Modern North American cider making, working from research on juice nitrogen and fermentation kinetics, typically measures and feeds as a matter of routine. Traditional English and Spanish making generally does not feed at all, relying on the solids load of an unclarified juice and accepting a long, slow, cool ferment that finishes when it finishes. Normandy keeving inverts the whole question: the point of the process is to remove nitrogen so that the yeast runs out of resources and leaves residual sugar, and adding nutrient to a keeved juice would destroy the method. A maker therefore needs to know which of these they are doing before deciding whether feeding is prudent or self-defeating.
Done badly, the errors are recognisable. Feeding after fermentation is well advanced does little, because the transport systems that take up ammonium are downregulated once growth has stopped, so a late addition to a stuck ferment often sits there unused. Feeding too much produces a hot, fast ferment that blows aroma off with the gas and leaves fusel alcohols and residual nitrogen behind for spoilage organisms to find. Feeding blind, without any sense of what the juice started with, is the underlying error in both cases. Quantities are not something to take from a general reference: they depend on the juice analysis, the yeast strain and the sugar load, and the correct source for them is the yeast manufacturer’s guidance applied to a measured juice.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Fermentation
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.
Fermentation
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.
Fermentation
Fermentation monitoring
Watching a running ferment through gravity, temperature, smell and surface behaviour, and reading the rate of change rather than any single figure.
Juice treatment
Juice clarification
The deliberate use of enzyme, fining agents or mechanical separation to produce a bright juice before fermentation, and what that costs the ferment.
Fermentation
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.
Fermentation
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.
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.
- How long does cider take to ferment — A warm ferment with cultured yeast can finish in one to two weeks; a cool wild ferment in a cellar may take three months or more. Slow is not the same as stuck — the test is whether gravity is still falling.
- Can you make cider from shop bought apple juice — Yes, provided the juice contains no preservative — check for potassium sorbate or benzoate on the label. Pasteurised juice ferments perfectly well once yeast is added, because pasteurisation removes the organisms but not the sugar.
- How do i restart a stuck cider fermentation — Warm the batch gently, then build an active starter and acclimatise it to the cider in stages rather than pitching dry yeast straight in. Yeast dropped into a cold, alcoholic, nutrient-poor liquid usually dies without restarting anything.
- What is keeving — Keeving is a technique for starving a ferment of nitrogen so that it stops before all the sugar is gone, leaving a naturally sweet cider. Pectin is made to gel and float as a brown cap, carrying nutrients and yeast out of the juice with it.
- 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.
- 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.
Where to go next
- How cider is made — The whole sequence, stage by stage, with the choices open at each one.
- Cider science — The chemistry and microbiology the methods on this page rest on.
- Troubleshooting — What goes wrong, how to recognise it, and whether it can be reversed.
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.
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.
Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264 · peer-reviewed literature · passage verified 2026-08-24 · covers 2016
Open access; read in full on 2026-08-24. This is the paper CiderHQ cites against the folk rule that low nitrogen causes sulphide and adding nutrient cures it. Two Saccharomyces strains fermented the same Cornell juice at three nitrogen levels: one strain produced no detectable hydrogen sulphide at any level, and in the strain that did, the middle nitrogen treatment produced the most — twice the low treatment and six times the high. A rule that is true on average is being applied to individual batches where it can be exactly backwards, and the correction is worth a page of its own.
Boudreau, Peck, O’Keefe and Stewart, Food Science & Nutrition 6(1):119–123 · peer-reviewed literature · passage verified 2026-08-24 · covers 2014–2015
Open access; read in full on 2026-08-24. The paper that gives cider its own nitrogen numbers instead of borrowing wine’s. A hundred and eight apple samples from Virginia over two seasons, with the two fractions of assimilable nitrogen measured separately — which matters, because the finding is that apple juice is short of ammonium specifically, and that the wine practice of measuring both fractions may be unnecessary for apples while the wine practice of assuming there is enough nitrogen is badly wrong.