Organism
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
Also called brewer’s yeast, wine yeast, cider yeast.
- Kind
- Yeast
- Binomial
- Saccharomyces cerevisiae
- Role
- Primary fermentation, Secondary fermentation, Present throughout
What it does
- Converts glucose, fructose and sucrose to ethanol and carbon dioxide by glycolysis, running fermentatively even in the presence of oxygen — the Crabtree effect — which is why it dominates a sugar-rich juice rather than simply respiring it.
- Tolerates ethanol far better than the species that precede it, so it inherits the ferment rather than winning it outright: it is usually a minority of the population at pressing and a near-monoculture by the time the gravity is down.
- Produces glycerol, succinic acid and higher alcohols as by-products of nitrogen and redox metabolism, and ethyl esters of fatty acids that carry much of the fermentation aroma of a finished cider.
- Releases hydrogen sulphide and, at the extreme, mercaptans when assimilable nitrogen runs short — the single commonest cause of a cider that smells reduced, and the reason cider juice is often nitrogen-limited in a way grape must is not.
- Autolyses after the ferment, releasing mannoproteins and amino acids that build texture during lees ageing and feed whatever comes next.
- Arrives late in a spontaneous ferment rather than early. In Asturian musts pressed pneumatically it was absent from the first day’s isolates entirely and reached the majority only in the closing stages; the organism that finishes the ferment is not the organism that starts it.
- Produces hydrogen sulphide, or does not, according to strain before anything else. Two commercial strains fermenting the same Cornell juice at the same temperature gave 288 micrograms per 100 millilitres and nothing at all, across every nitrogen treatment tested.
Conditions it works in
What the organism tolerates and what suppresses it. These are the levers a maker actually has: temperature, acidity, air, alcohol and sulphite.
| Condition | What is recorded |
|---|---|
| Temperature | Grows from roughly 4 °C to 35 °C. Cider ferments are commonly held between 12 °C and 20 °C; cooler ferments run slower, retain more acetate esters and lose less aroma to the airlock, while ferments above about 25 °C tend towards a coarser, hotter character. |
| pH | Comfortable across the whole cider range, roughly pH 3.0–4.2, and still active below pH 3.0 where most bacteria are suppressed. |
| Oxygen | Facultative. Needs a small early oxygen exposure to build sterols and unsaturated fatty acids for membrane integrity, then ferments anaerobically; oxygen later in the ferment is a liability rather than a help. |
| Alcohol tolerance | Routinely completes to 12–14% ABV and selected strains beyond that — comfortably above anything a cider ferment reaches unaided. |
| Sulphite tolerance | Relatively tolerant. Normal juice sulphiting extends its lag phase rather than preventing it, which is exactly the intended effect: the sensitive wild population is held back while *Saccharomyces* starts. |
What it produces
Compounds this organism makes. Which organism made a compound usually decides whether it reads as a feature or as a symptom.
Ethanol
The alcohol yeast makes from fruit sugar, which converts a perishable juice into a keepable drink and carries most of its aroma to the nose.
Carbon dioxide
The other product of fermentation, which protects a cider from air while it is being made and, dissolved in the finished drink, changes both its texture and its perceived acidity.
Glycerol
A syrupy three-carbon alcohol yeast produces as a side reaction of fermentation, which adds weight to a dry cider and is the raw material for one of its more obscure faults.
Succinic acid
An acid made by the yeast rather than the fruit, which adds a salty-bitter edge to a dry cider and, unlike malic acid, cannot be removed by malolactic fermentation.
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.
Isoamyl alcohol
The most abundant fusel alcohol in cider, made from leucine, and the direct precursor of the banana ester that defines warm-fermented styles.
2-Phenylethanol
The yeast-made alcohol responsible for the rose and honey note in cider, produced from phenylalanine and one of the few floral aromas that is not carried in from the fruit.
Ethyl hexanoate
One of the most powerfully aromatic esters in cider, perceptible at a few micrograms per litre, contributing green apple and aniseed to the fruit complex.
Ethyl octanoate
A medium-chain ethyl ester contributing ripe pear and a waxy sweetness, and one of the compounds that makes an ester-forward cider feel rounder as well as fruitier.
Acetaldehyde
The compound sitting one step short of ethanol, which smells of bruised apple and sherry, binds most of the sulphite added to a cider, and is the chemical signature of oxidation.
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.
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
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.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Yeast haze
Cloudiness from yeast cells that have not settled out, usually because the strain flocculates poorly or the cider has not been left alone long enough.
Bottle over-carbonation
More dissolved carbon dioxide in the bottle than intended or than the glass is rated for — a presentation problem at the mild end and a physical hazard at the severe one.
Acetaldehyde excess
A bruised-apple, green-nut or sherry aroma from acetaldehyde, produced by oxidation, by film yeast, or left behind by a ferment that was interrupted.
Gushing
Cider that erupts from the bottle on opening, either because it is over-pressurised or because something in it is nucleating the dissolved gas violently.
Patulin contamination
Contamination of juice or cider with patulin, a mycotoxin produced by *Penicillium expansum* in rotting apples — a genuine food-safety question rather than a flavour one.
Excess diacetyl
A butter, butterscotch or popcorn character from diacetyl, produced by lactic acid bacteria metabolising citric acid, and by yeast under stress.
Excessive sediment
More deposit in the bottle or vessel than the presentation intends, ranging from a normal conditioning yeast layer to a loose sludge that clouds every pour.
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.
Under-carbonation
A cider intended to sparkle that has little or no dissolved gas, usually because the bottle conditioning never started or the closure did not hold.
Atypical ageing
A cider that loses its fruit unusually early and develops a flat, faintly acrid or naphthalene-like character — a syndrome described in white wine and less firmly established in cider.
Where in the process it appears
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.
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.
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.
Yeast rehydration
Reviving active dried yeast in warm water before pitching, so the cells restore their membranes without being ruptured by the sugar concentration of juice.
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 temperature control
Managing the temperature at which a ferment runs, which sets not only how fast it goes but which aromatics survive it and what the finished cider tastes of.
Microbial succession
The ordered handover of a spontaneous ferment from apiculate yeasts to *Saccharomyces* to lactic acid bacteria, and the spoilage organisms waiting at the end of it.
Secondary fermentation
Any fermentative event that follows the primary ferment — residual sugar refermenting, a deliberate second alcoholic fermentation, or the malolactic conversion of the maturation phase.
Bottle conditioning
Carbonating cider by letting a second fermentation finish inside the sealed bottle, so the gas is generated where it is going to stay.
Ice concentration
Freezing pressed juice and drawing off the unfrozen fraction, so that water is removed as ice and everything else in the juice is left behind more concentrated.
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.
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.
Sulphiting
Adding sulphur dioxide to juice to suppress spoilage organisms and oxidative browning, at a level that only means anything once the juice pH is known.
Back-sweetening
Adding sugar, juice or concentrate to a cider that has fermented dry — a straightforward adjustment that leaves the drink microbiologically unstable until something is done about it.
Pasteurisation
Heating cider enough to inactivate the organisms that would spoil it, either in the sealed package or in-line before filling, at a measurable cost in fresh aroma.
Patulin control
Managing the mycotoxin produced by rot fungi in damaged apples, which is controlled by fruit selection rather than by any treatment applied to juice.
Arrested fermentation
Deliberately halting a ferment while sugar remains, to obtain natural sweetness from the fruit rather than from an addition — and accepting the instability that follows.
Cold chain
Keeping an unpasteurised, unfiltered or back-sweetened cider refrigerated from the packaging hall to the point of sale, because refrigeration is the only thing holding it stable.
Fermentation monitoring
Watching a running ferment through gravity, temperature, smell and surface behaviour, and reading the rate of change rather than any single figure.
Fermentation vessels
The container a cider ferments in — wood, stainless, plastic, glass or concrete — and how its permeability, thermal mass and resident microflora shape the result.
Juice pasteurisation
Heat treatment of juice before fermentation, which inactivates enzymes and microorganisms, and in doing so removes the wild flora that would otherwise ferment it.
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.
Natural carbonation
Bottling before the primary fermentation has finished, so the sugar still in the cider produces the carbonation with nothing added and nothing restarted.
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.
Priming
Adding a measured, calculable quantity of fermentable sugar at bottling so that the fermentation which follows generates a predictable volume of carbon dioxide.
Sorbate stabilisation
Adding potassium sorbate to prevent yeast from restarting a fermentation in the package — an inhibitor rather than a killer, and one that must never be used without sulphite.
Sterile filtration
Membrane filtration at a rating that retains viable yeast and bacteria, which is what allows a sweet cider to be shelf-stable without heat or preservative — provided the filling that follows is aseptic.
Tank conditioning
Running a second fermentation in a sealed pressure tank so the gas is generated by yeast but the sediment never reaches the bottle.
Tank maturation
Resting cider in stainless steel or a lined vessel, where the point of the container is that it contributes nothing and admits almost no oxygen.
Traditional method
A second fermentation in the bottle the cider will be sold in, followed by riddling the deposit into the neck and expelling it, so the drink is both bottle-fermented and clear.
Centrifugation
Separating solids from cider by density in a rapidly spinning bowl, continuously and without a filter medium, at the price of shear and oxygen pick-up.
Cold maturation
Holding cider at low temperature so that it settles bright, sheds colloidal material and stops changing microbially, without any additive or treatment being applied.
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.
Transfer method
Fermenting in bottle for the character, then emptying the bottles under counter-pressure into a tank, filtering and refilling to remove the deposit without riddling.
Measured figures
Growth limits, tolerances and population counts, shown with the context each was taken in rather than averaged into a constant.
Microbial population7.0 log CFU/mL
Ithaca, New York, United States, 2016 · Inoculation rate for laboratory cider fermentations at 20 °C, stated as 1 × 10⁷ cells/mL · Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264
An inoculation rate a laboratory chose, not a population a cider reaches. It is recorded because it is the pitch rate behind that study’s sulphide results, and because it gives a reference point: a commercial pitch aims for the same order of magnitude, and a spontaneous ferment gets there by growth over several days instead.
Viable cells per millilitre, on the log scale. What separates an organism that is present from one that is running the ferment. Measured in log colony-forming units per millilitre.
Fermentation temperature20.0 °C
Ithaca, New York, United States, 2016 · Temperature-controlled room, held constant across all treatments · Song, Gibney, Cheng, Liu and Peck, Frontiers in Microbiology 11:1264
The temperature of a controlled experiment rather than a recommendation. It is worth setting against the 12–15 °C of an Asturian cellar recorded on this site: the same species at those two temperatures makes measurably different quantities of glycerol and of aroma, so a fermentation temperature is part of the description of any result obtained at it.
The temperature a ferment was actually run at, which governs how much aroma is made and how much is blown off with the gas. Measured in degrees celsius.
Described in full
- Shape
- Two stacked bar charts one above the other, each with four bars. Bars are sampling days 1, 4, 16 and 28 after pressing. Each bar is divided into three segments summing to 100 per cent, and every segment carries its own percentage as a number so the reading does not depend on seeing the fill.
- What is counted
- The share of identified yeast isolates belonging to each group, not the number of cells. A group at 100 per cent was the only thing cultured from that sample; it does not mean nothing else was alive.
- The three groups
- Apiculate yeasts are Hanseniaspora valbyensis, H. uvarum and H. osmophila. Oxidative non-Saccharomyces are Metschnikowia pulcherrima and Pichia guillermondii. Saccharomyces is S. bayanus and S. cerevisiae together.
- Upper chart, pneumatic pressing
- Day 1: apiculate 84, oxidative 16, Saccharomyces 0. Day 4: apiculate 4, oxidative 10, Saccharomyces 86. Day 16: Saccharomyces 100. Day 28: apiculate 38, Saccharomyces 62. This is the textbook succession — non-Saccharomyces first, then a Saccharomyces takeover — except for the tail, where an apiculate yeast comes back at more than a third of isolates.
- Lower chart, traditional pressing
- Day 1: apiculate 66, oxidative 14, Saccharomyces 20. Day 4: apiculate 48, oxidative 4, Saccharomyces 48. Day 16: apiculate 90, Saccharomyces 10. Day 28: apiculate 94, Saccharomyces 6. Here the succession does not happen. Saccharomyces is present from the first day, never dominates, and the ferment finishes overwhelmingly apiculate.
- Why it matters
- Both ferments completed. Both gave dry cider of 6.4 to 6.5 per cent alcohol. The difference between them was how the fruit was pressed, and the account of cider fermentation as a fixed sequence of organisms does not survive it. Apiculate yeasts are usually described as dying out within days under rising alcohol; at 12 to 15 degrees Celsius, without sulphite, and on a must under 110 grams of sugar per litre, one of them ran the whole ferment.
- What this is not
- One cellar, one harvest, four ferments. It is evidence that the succession varies, not a measurement of how often it varies this way.
About Saccharomyces cerevisiae
Saccharomyces cerevisiae is the organism most people mean when they say “yeast”, and in cider it occupies a specific and slightly counter-intuitive position. It is rarely abundant on sound apple skins. Its reservoirs are the mill, the press, the pipework, the vessel and the cellar air of a place that has fermented before, which is why a first season in a new building often ferments differently from the tenth. In freshly pressed juice it is usually outnumbered by apiculate yeasts by a wide margin, and it becomes dominant not by growing faster but by still growing when they have stopped.
That handover is the hinge of a spontaneous ferment. Once ethanol reaches roughly 3–5% ABV and the dissolved oxygen is gone, most non-Saccharomyces species cease dividing, and everything from there — the last two thirds of the sugar, the bulk of the ethanol, the ethyl esters, the glycerol — is Saccharomyces work. An inoculated ferment simply performs the same handover deliberately and earlier, by adding enough active dry yeast that the apiculate phase is short.
Cider’s characteristic problem with this yeast is nitrogen. Apple juice frequently carries less assimilable nitrogen than yeast needs to ferment its sugar cleanly, and a nitrogen-starved population signals its distress by producing hydrogen sulphide and by slowing or stalling short of dryness. Whether that is a fault or a feature depends on the maker: keeving is a deliberate nitrogen starvation, engineered to stop the ferment with sugar still in the cider, and the same physiology that spoils a careless ferment is what makes a cidre doux possible.
Strain differences within the species are large and are the subject of a substantial commercial literature, but CiderHQ does not make strain-level claims. What can be said at species level is that S. cerevisiae is tolerant of alcohol, of low pH and of sulphite; that it is the only organism in the cider succession reliably able to take a juice to dryness; and that its by-products are as much a part of a cider’s flavour as the fruit’s own.
One correction is worth making explicitly, because it is repeated everywhere and the evidence does not support it. Hydrogen sulphide in cider is habitually explained as a nitrogen deficiency, with the remedy being to add nutrient. Two strains fermenting one Cornell juice at three nitrogen levels say something more awkward. One strain made no detectable sulphide at any nitrogen level at all. The other made most of it at the middle level — twice what it made at the lowest addition and six times what it made at the highest. Strain came first, the relationship was not monotonic, and a maker who adds a modest dose of nutrient to a batch that is already gassing may be moving towards the worst part of the curve rather than away from it. The rule is a population average being applied to a batch.
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 does cider ferment — Yeast consumes the sugar in apple juice and produces roughly equal masses of ethanol and carbon dioxide, along with the esters and higher alcohols that give cider much of its aroma. In a wild ferment several yeast species take turns before *Saccharomyces* finishes the job.
- What temperature should cider ferment at — Most cider is fermented cool, commonly between about 12 and 18 °C. Cooler ferments keep more fruit aroma and run slower; above the low twenties the cider tends towards hot, solvent-like higher alcohols.
- 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.
- 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.
- 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 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
- All organisms — Grouped by what each does in the ferment, and by what kind of organism it is.
- Compounds — The chemistry this microbiology produces.
- Troubleshooting — Work from the symptom in the glass back to the organism.
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.
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.
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.
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.
Yeast species associated with the spontaneous fermentation of cider
Suárez Valles, Pando Bedriñana, Fernández Tascón, Querol Simón and Rodríguez Madrera, Food Microbiology 24(1):25–31 · peer-reviewed literature · passage verified 2026-08-24 · covers 2001–2002
SERIDA’s survey of what is actually growing in an Asturian cellar during a spontaneous ferment, across two harvests and two pressing technologies. Read in full from the author institution’s open repository (ria.asturias.es, handle 123456789/925) on 2026-08-24. Two things make it worth citing rather than summarising: it identifies its isolates molecularly rather than by colony appearance, and it publishes the analytical composition of the finished ciders alongside the microbiology, so a reader can see the organisms and the numbers they produced in the same paper. It also contradicts the textbook account of apiculate yeasts dying out early, which is why CiderHQ cites it on that point specifically.
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.