Compound
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.
Also called H2S, Rotten egg gas.
- Class
- Sulphur compounds
- Formula
- H2S
- How often it matters
- Regularly encountered
What it does in cider
- Is generated when yeast reduces sulphate to sulphide for amino acid synthesis and then has no nitrogen skeleton to attach the sulphide to, so it leaves the cell as gas.
- Signals nitrogen deficiency more reliably than any other sensory cue, which is why it appears in cider far more often than in wine.
- Can be stripped by racking with aeration or removed by copper, but only while it remains as the free gas.
- Reacts onwards to mercaptans and disulphides that no simple treatment removes, so a delay of days converts a fixable problem into a permanent one.
How it is perceived
What the compound registers as, and at roughly what concentration. Perception is not a property of the molecule alone: sugar, tannin and carbonation all change where a threshold falls.
- rotten egg
- drains
- struck flint at trace level
- sewage
One of the lowest detection thresholds of any compound in fermented drinks, in the region of a microgram per litre, which is why it is smelled long before any analysis would find it.
Descriptors it is responsible for
Sensory records that name Hydrogen sulphide as a cause. Each states the perception and the mechanism behind it.
- Rotten egg — Hydrogen sulphide from yeast under nitrogen stress — the commonest sulphur fault and the most correctable.
- Drains — A heavy, stagnant, sewer-like note from mercaptans formed when hydrogen sulphide is left to react.
- Flinty — A sub-threshold reductive note read as struck flint rather than as sulphur, the mildest state of reduction.
- Fresh yeast — The clean, faintly sulphidic smell of an active yeast population, met in young cider and during fermentation.
- Raspberry — A raspberry aroma arising in unfruited cider from bacterial spoilage — the French *framboisé* — as well as from added fruit.
- Wet stone — A cool, damp, faintly mineral impression, in cider a product of low-level sulphur compounds and high acidity rather than of minerals.
- Fermenting vat — The pungent, CO2-lifted smell of a ferment in full activity, met in very young cider straight from the vessel.
- Garlic — A pungent allium note from specific thiols and disulphides, occasionally from orchard spray residues.
The structure it moves
| Dimension | What it is |
|---|---|
| Fermentation character | Aromas made by the ferment rather than carried in from the fruit. |
| Freshness | Whether the drink smells and tastes of live fruit or of time and air. |
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.
Aroma detection threshold0.41 µg/L
context not recorded · Sensory threshold quoted in a cider fermentation study, stated as >0.00041 mg/L · Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264
Four hundred nanograms in a litre. That is why a compound present in quantities no gravity reading would ever notice can be the first thing anybody says about a cider. The paper states the threshold rather than measuring it, and thresholds are matrix-dependent — sugar, tannin and carbonation all change what a nose finds — so treat it as the order of magnitude rather than a number to compare a batch against.
The concentration at which a compound becomes perceptible — which is why a trace compound can matter more than an abundant one. Measured in micrograms per litre.
Fermentation duration24–192 h
Ithaca, New York, United States, 2016 · Sulphide detection tubes on fermentations at 20 °C, strain UCD522 · Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264
The window in which sulphide was released at all. It began 24 hours after inoculation in the high-nitrogen treatment and 72 hours in the low and intermediate ones, and had stopped in every case by 192 hours — so a cider that smells of sulphide in the second week is describing something that happened in the first.
How long a stage of fermentation took under stated conditions. Never a prediction — the same juice at another temperature behaves differently. Measured in hours.
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
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.
Lees ageing
Deliberately holding a cider or perry on its fine yeast deposit so that autolysing cells release material that changes texture and foam behaviour.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
Racking
Moving cider off the sediment it has thrown, which both cleans the liquid and — by taking yeast and nitrogen away with the deposit — slows what is left of the ferment.
Oxygen management in fermentation
Giving the yeast the oxygen it needs early to build viable membranes, then excluding it once fermentation is under way and especially once it slows.
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.
Fining
Adding a reactive agent that binds a target colloid and carries it to the bottom, chosen according to whether the problem is tannin, protein or a phenolic taste fault.
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.
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.
Reduction
A closed, stale, slightly sulphurous character in cider held under strongly oxygen-free conditions, sometimes clearing with air and sometimes not.
Mercaptan taint
Onion, garlic, burnt rubber and cooked-cabbage aromas from thiols and disulphides formed when hydrogen sulphide is left in cider long enough to react onwards.
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.
Light strike
A skunky, cooked-cabbage or drain-like aroma produced when light acting on riboflavin generates sulphur compounds in a bottle.
Framboise
A raspberry-and-rotten-fruit character with sulphurous overtones, produced by *Zymomonas mobilis* in sweet ciders that still contain sugar.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
Saccharomyces bayanus
A name applied both to a hybrid *Saccharomyces* lineage and, loosely, to a whole class of commercial high-alcohol yeasts, and one of the least stable names in fermentation microbiology.
Saccharomyces uvarum
A cold-tolerant relative of *S. cerevisiae* recovered from spontaneous cider and wine ferments, associated with low-temperature fermentation and higher glycerol.
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 Hydrogen sulphide
Yeast needs sulphur to make cysteine and methionine, and it gets it by taking sulphate from the juice and reducing it, step by step, to sulphide. The sulphide is then supposed to be joined immediately to a nitrogen-containing precursor. If the yeast has no nitrogen to spare, the sulphide has nowhere to go, and it leaves the cell as hydrogen sulphide. The smell of a ferment going wrong is, in the most literal sense, the smell of a yeast that has run out of nitrogen halfway through a biosynthetic pathway.
This is why the fault is so much more common in cider than in wine. Apple juice is chronically short of assimilable nitrogen; grape must usually is not. A cider ferment that produces hydrogen sulphide is not unlucky, it is under-fed, and the fault is better understood as a nutritional symptom rather than a hygiene one.
Timing decides whether it can be fixed. As free gas it is volatile and reactive: racking with a splash, stirring, or a small copper addition will remove it, and the cider recovers completely. Left in contact with the cider, it reacts with ethanol and other components to form mercaptans, and mercaptans oxidise to disulphides. Neither responds well to the treatments that work on the gas, and disulphides are effectively permanent. A ferment that smells of rotten egg should be dealt with in days, not weeks.
The genuine solution is upstream. Measuring assimilable nitrogen before pitching, and feeding the ferment at the right point rather than after the smell appears, prevents the whole sequence. It is also worth noting the alternative source: elemental sulphur used as an orchard fungicide can carry into juice on the fruit and be reduced by yeast in exactly the same way, which is one of the few places where a spray programme reaches directly into a fermentation.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Sulphur compounds
Mercaptans
What hydrogen sulphide becomes if it is left alone: onion, garlic and rubber notes that are far harder to remove than the gas they came from.
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
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.
Sulphur compounds
Dimethyl sulphide
A sulphur compound that reads as cooked vegetable in quantity and adds an indefinable savoury depth in trace, and which builds slowly during storage rather than during fermentation.
Additives and processing aids
Sulphur dioxide
The antimicrobial and antioxidant on which most modern cidermaking depends, and whose effectiveness collapses as pH rises — which makes every sulphiting decision a pH decision first.
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.
- Does cider contain sulphites — Most does. Sulphur dioxide is added to protect juice and finished cider, and fermentation itself produces a small amount even when none is added. European labels must declare it above 10 mg per litre.
- 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.
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.
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.
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.
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.