Sensory descriptor
Rotten egg
Hydrogen sulphide from yeast under nitrogen stress — the commonest sulphur fault and the most correctable.
Also called Hydrogen sulphide, Bad egg, Sewer gas.
- Aroma family
- Sulphur
- Does it indicate a fault?
- Usually, yes
What causes it
Yeast reduces sulphate to sulphide as part of the sulphate assimilation pathway, in order to build the sulphur-containing amino acids cysteine and methionine. Where assimilable nitrogen runs short, the nitrogen skeletons needed to incorporate that sulphide are unavailable and the excess is released as hydrogen sulphide. Apple juice is naturally low in assimilable nitrogen — routinely under 100 mg/L, and sometimes under 50 — so this is a structural risk in cider rather than an occasional one. Elemental sulphur residues from orchard sprays, and excessive sulphite additions, both add to the pool.
Hydrogen sulphide has an odour threshold below one microgram per litre, so it is detectable long before it is a problem, and a trace during active fermentation is unremarkable. Caught early it is removed by aeration or splash racking. Left, it reacts with other components to form mercaptans and disulphides, which are far harder to remove.
The compounds responsible
Where the molecule is established. Some descriptors in this lexicon name a compound the compound register does not yet hold a record for; those are named in the cause above instead.
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.
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.
The organisms that make it
Where a specific organism is implicated rather than the fruit. Naming one answers a different question from naming a molecule: what is in the cellar, rather than what is in the glass.
What raises it
Processes that increase this character, or preserve it where it would otherwise be lost.
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.
Fermentation monitoring
Watching a running ferment through gravity, temperature, smell and surface behaviour, and reading the rate of change rather than any single figure.
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.
The fault it points at
Meeting this descriptor above a certain intensity is how the fault below is usually noticed first.
Fault
A rotten-egg or drain smell from hydrogen sulphide produced by stressed yeast, usually the first visible consequence of a nitrogen-short juice.
About Rotten egg
This is the fault where timing matters more than anything else. Hydrogen sulphide itself is volatile and can be blown off; its reaction products cannot, and the window between the two is measured in days.
Nitrogen management is the preventive control, and it is one of the clearest practical differences between cider and wine making: a grape must rarely needs the intervention that an apple must routinely does.
Others in the sulphur family
Rotten egg, struck match, drains, rubber, cooked cabbage.
Drains
A heavy, stagnant, sewer-like note from mercaptans formed when hydrogen sulphide is left to react.
Struck match
The sharp, mineral, matchhead note of free sulphur dioxide above its perception threshold.
Cooked cabbage
A vegetal sulphur note from dimethyl sulphide, rising slowly during storage rather than during fermentation.
Flinty
A sub-threshold reductive note read as struck flint rather than as sulphur, the mildest state of reduction.
Lightstruck
A skunky, sulphidic note produced when light degrades riboflavin in clear or green glass.
Rubber
A burnt-rubber note from disulphides and higher mercaptans, generally a late stage of reductive fault.
Garlic
A pungent allium note from specific thiols and disulphides, occasionally from orchard spray residues.
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.
- 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.
- 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.
- Does cider need oxygen to ferment — Yeast needs a little oxygen early on to build the sterols it uses to stay healthy, but the ferment itself is anaerobic. After the first days oxygen is a liability, because it feeds acetic acid bacteria and oxidises the cider.
- What is yeast nutrition in cider making
Where to go next
- The sensory model — The thirteen structural dimensions and the twenty aroma families, in full.
- Compounds — The chemistry behind the words.
- Troubleshooting — When a perception turns out to be a problem, this is where it is diagnosed.
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.
The New Cider Maker’s Handbook: A Comprehensive Guide for Craft Producers
Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against the Open Library union catalogue: Chelsea Green Publishing, 2013, ISBN 9781603584739, one edition recorded. That establishes the citation points at a real book in a stated edition, which is what a citation needs and is all it establishes. No copy was opened and nothing is quoted from it. The book itself is in print and not digitised in any open collection; where CiderHQ needs a figure from this territory it uses an accessible research source instead and says so.