Fault
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.
Also called rotten egg, H2S, sulphide.
- Severity
- Quality — the drink is worse for it
- Where it starts
- Fermentation, Juice treatment, Orchard, Maturation
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Fermentation
- Signs
- 5 recorded
What it is
Hydrogen sulphide is a gas produced by yeast during fermentation, mainly when the yeast is short of assimilable nitrogen. It has an extremely low odour threshold and smells of rotten eggs, drains or struck flint depending on concentration. Caught during active fermentation it is often the easiest cider fault to deal with, because carbon dioxide is still being generated and will carry it off. Left in the cider it reacts onwards into compounds that are far more stable and far harder to remove.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
On the nose
- A rotten-egg smell from the airlock or the top of the vessel during fermentation
- A drain or blocked-sink note in a young cider
- A struck-flint or matchstick edge at low concentration, easily mistaken for minerality
How the batch behaves
- A ferment that is also slow, stalling or unusually quiet — The nitrogen shortage that produces sulphide is the same shortage that slows the ferment.
On the palate
- A metallic, slightly sour taste in the finish
The words for it: Rotten egg, Struck match. Each links to what produces it.
When it appears. During active fermentation, usually in the first week, and typically when the ferment is most vigorous. A rotten-egg smell that first appears months later is almost certainly something else.
Detectable at very low concentration — this is among the most readily smelled compounds in a cider house — which is why it is usually caught while it can still be dealt with by splash-racking. That short window is the whole practical significance of the fault.
Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264, Andrew Lea
What it is mistaken for, and how to tell
One observation per rival, chosen because it separates them rather than because it describes either. Several of these are not faults at all — a style feature, a normal outcome, or the fruit behaving as it does.
- Reduction — Hydrogen sulphide is unmistakably rotten egg; general reduction is struck match, flint or cooked cabbage. Sulphide is a stage that reduction can follow.
- Mercaptan taint — Time. Untreated hydrogen sulphide reacts onwards to mercaptans within weeks, and the smell shifts from rotten egg towards drains, rubber and garlic. Once it has shifted, the window for the easy remedy has closed.
- Sulphur dioxide excess — Sulphur dioxide is a sharp, prickling struck-match note that catches the back of the nose; hydrogen sulphide is putrid rather than sharp.
What is actually happening
The chemistry or microbiology behind it. Understanding the mechanism is what makes the prevention make sense rather than being a list of rules.
Yeast needs sulphur to build the amino acids methionine and cysteine. It obtains it by taking up sulphate from the juice and reducing it, through the sulphate reduction pathway, to sulphide. Sulphide is then normally fixed immediately onto a nitrogen-containing carbon skeleton to make those amino acids.
If the yeast runs short of assimilable nitrogen, the acceptor molecules are not available, and the sulphide generated by the pathway has nowhere to go. It leaves the cell as hydrogen sulphide gas. This is why a fault that smells of sulphur is nearly always a nitrogen problem, and why adding sulphur-containing anything makes it worse rather than better.
Cider juice is characteristically low in yeast assimilable nitrogen compared with grape must, particularly juice from traditional bittersweet fruit grown in unfertilised orchards, and this is the central reason the fault is common in cider and less so in wine. Thiamine deficiency and elemental sulphur residues from orchard sprays are secondary contributors.
The compound is highly volatile and, while fermentation is vigorous, is stripped continuously by the escaping carbon dioxide. Once the ferment slows, hydrogen sulphide remaining in the cider begins to react with ethanol and with other components to form thiols and disulphides, which are much less volatile, smell of onion, rubber and cooked cabbage, and do not blow off.
Which sulphur smell is it?
Five different problems all get called a sulphur smell, and they are not equally serious: one is a signal to act this week, one is permanent, one fades on its own, one disappears in the glass and one is a storage mistake. Three questions separate them, asked in this order. When did it first appear? Does it lift after a hard pour and five minutes in the glass? And what was done to the cider, or where was it kept, just before?
| What it smells of | First appears | After a hard pour and five minutes | What it means for the batch |
|---|---|---|---|
| Rotten egg, strongest at the airlock | During active fermentation, usually the first week | Lifts: it is volatile and leaves with the gas | Hydrogen sulphide. Recoverable if dealt with while the ferment is still running |
| Drains, rubber, onion, garlic, boiled cabbage | Weeks later, during maturation, from sulphide left untreated | Stays, however long it is swirled | Mercaptans. Aeration no longer helps, and the batch is usually lost |
| Struck match, with a prickle high in the nose | Straight after a sulphite addition | Little change in minutes; falls slowly over days of rest | Sulphur dioxide excess. Ask what was added and when |
| Flint, a closed nose, “bottle stink” on opening | After long airless storage, sometimes months after bottling | Lifts substantially, often within ten or fifteen minutes | Reduction. Decant or open ahead of serving |
| Skunk or cabbage, in clear or green glass | After packaging, over days to weeks in light | Stays | Light strike. Irreversible in the bottle; the rest of the stock goes into the dark |
- Mercaptan taint — what sulphide turns into, and why it cannot be aerated away.
- Excess sulphur dioxide — the struck-match note, and how long it takes to fall.
- Reduction — the closed, flinty bottle that opens in the glass.
- Light strike — the skunky bottle, and the shelf pattern that gives it away.
- Fault finder — work through the signs, the stage and the rivals for any fault, not only these five.
What one controlled cider ferment showed
The usual advice — sulphide means too little nitrogen, so add nutrient — is half right, and a controlled experiment on cider juice shows which half. One juice, short of nitrogen at 63.7 mg/L, was fermented at 20 °C by two yeast strains at three levels of added nitrogen, and the gas each ferment gave off was measured.
Three findings change what a maker should do. The strain mattered first: one produced no detectable sulphide at any nitrogen level, so the cheapest prevention is often the choice of yeast. In the strain that did produce it, the middle level of nitrogen produced the most — more than twice the unsupplemented ferment — so a token addition can make matters worse rather than better. And the sulphide came early and stopped: it began after one to three days and had finished by the eighth.
| Nitrogen added | Strain that produced sulphide | Strain that did not |
|---|---|---|
| Low | About 124 µg | None detected |
| Intermediate | About 288 µg — the most | None detected |
| High | About 44 µg | None detected |
| When it appeared | From 24 h at the high level, 72 h at the others; over by 192 h | — |
How it happens
| Cause | Stage | How often |
|---|---|---|
| Juice low in yeast assimilable nitrogen, especially from unfertilised traditional orchards | Fermentation | common |
| A juice clarified very thoroughly before fermentation, removing solids that carried nutrient | Juice treatment | occasional |
| Yeast strain selected without regard to its nitrogen demand | Fermentation | occasional |
| Elemental sulphur residue on fruit from late orchard sprays | Orchard | occasional |
| Fermentation temperature high enough to stress the yeast population | Fermentation | occasional |
| Cider left on heavy lees after fermentation, where autolysing yeast releases sulphur compounds | Maturation | occasional |
Can it be put right?
Most cider faults cannot be reversed. Where that is the answer it is given plainly — an honest 'this batch is what it is' is more useful than a procedure that will not work.
| Option | Effectiveness | What it involves |
|---|---|---|
| Rack the cider with deliberate splashing while fermentation is still active | Reliable | The standard response and genuinely effective, because hydrogen sulphide is volatile and the carbon dioxide still being produced protects the cider from the oxygen introduced. This only holds during active fermentation — the same action on a finished cider oxidises it. |
| Add yeast nutrient at the first sign, early in the ferment | Partial | Addresses the cause rather than the symptom, but only while there is enough fermentation left for it to matter. Use the supplier’s rate for the product; nutrient blends differ substantially in composition. |
| Wait for it to blow off on its own | Partial | Often works during a vigorous ferment. Risky as a strategy, because the window closes when fermentation slows and what remains converts to compounds that will not leave. |
| Remove sulphide from a finished, aged cider | Unlikely to work | Copper treatment is used commercially and is not something to improvise: copper is itself a taint and an oxidation catalyst, dosing is tightly regulated, and residual copper limits apply. If the cider has aged, the compounds present are probably no longer hydrogen sulphide at all. |
CiderHQ gives no additive dosage figures. An addition is a food-safety decision that depends on legal limits, on the juice in front of you and on what you are protecting against, and the right figure comes from your supplier’s or regulator’s own guidance rather than from a general reference.
Preventing it
- Measure or estimate the juice nitrogen rather than assuming it is adequate; cider juice frequently is not.
- Where nutrient is added, follow the manufacturer’s stated rate and timing for the product in hand, and add it early in fermentation rather than at the end when it does little good and can feed spoilage organisms.
- Choose a yeast whose published nitrogen requirement suits the juice available.
- Avoid stripping juice of all solids before fermentation unless the process specifically calls for it.
- Rack off gross lees within a reasonable time rather than leaving cider on a thick yeast bed indefinitely.
- Observe the harvest interval for any sulphur-containing orchard treatment.
Hydrogen sulphide is the fault that rewards paying attention, because the difference between a nuisance and a permanent problem is measured in days. During a vigorous ferment it is a signal, not yet damage; a fortnight later it is a different set of molecules that no amount of racking will shift.
It is also the most direct sensory evidence of the structural nitrogen problem in cider. Apple juice from traditional orchards, particularly from bittersweet fruit on unfertilised standard trees, is often substantially poorer in assimilable nitrogen than grape must, and much of what goes wrong in cider fermentation traces back to that single fact.
A common misreading is to treat the smell as an infection. It is not: it is ordinary brewing yeast doing ordinary metabolism under stress, and the vessel is not contaminated. The response is nutritional and physical, not sanitary.
At the very low end the same compound is not necessarily unwelcome. A faint struck-flint character in a young cider is often read as minerality, and whether that is a fault is a question about the drink intended rather than about the chemistry.
The compounds involved
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.
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.
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.
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.
Thiamine
A vitamin yeast cannot ferment without, frequently limiting in cider juice, and destroyed by the sulphite added to protect that juice.
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.
The organisms involved
Where in the process it arises
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.
Nutrient addition
Supplementing a characteristically nitrogen-poor juice so that yeast can complete fermentation without producing sulphide or stalling.
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.
Yeast selection
Choosing which cultured strain to pitch, on the basis of the temperature, nitrogen, alcohol and aroma behaviour that separates one commercial yeast from another.
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 clarification
The deliberate use of enzyme, fining agents or mechanical separation to produce a bright juice before fermentation, and what that costs the ferment.
Faults it is confused with
These present similarly. What separates them is set out on each page.
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.
Reduction
A closed, stale, slightly sulphurous character in cider held under strongly oxygen-free conditions, sometimes clearing with air and sometimes not.
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.
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.
Where this comes up in a guide
The link lands on the step where the fault arises rather than at the top of the pathway, because that is where the decision that causes it is taken.
How cider is made, start to finish
How is cider actually made?
How to taste cider and perry
How do I taste cider properly?
Making perry
How do I make perry, and what is different about it?
When the fermentation is not doing what it should
My fermentation is doing something strange. What is going on?
Your first batch of cider
I have apples and no equipment. What do I actually do?
From sound cider to good cider
I can make cider without faults. How do I make it better?
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.
- What yeast should i use for cider — CiderHQ does not recommend brands. The choice is between a neutral, reliable strain that lets the fruit show, an aromatic wine strain that adds its own esters, and no addition at all. Alcohol tolerance, cold tolerance and nitrogen demand are the properties worth comparing.
- What does a nitrogen-starved cider taste like
- Why is my cider fermenting so slowly
- 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.
- What is racking in cider making — Racking is siphoning cider off the sediment it has thrown into a clean vessel, leaving the lees behind. It clarifies the cider and, in traditional practice, is also used to slow a ferment by removing yeast with the lees.
Where to go next
- The fault finder — Describe what you can smell and see, and narrow it down from the signs.
- All faults — Grouped by where they come from and how serious they are.
- Cider science — The chemistry and microbiology these faults come out of.
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.