Compound
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.
Also called Ethyl alcohol, Alcohol.
- Class
- Alcohols
- Formula
- C2H5OH
- How often it matters
- Present in every cider
What it does in cider
- Replaces sugar as fermentation proceeds, so the drink loses sweetness and gains warmth, weight and a faint sweetness of its own at the same time.
- Preserves. Above roughly 4% it suppresses most of the organisms that would otherwise turn juice to spoilage, which is the original reason cider exists rather than apple juice.
- Acts as the solvent for aroma. Volatile esters and phenols partition between liquid and headspace differently as alcohol rises, so the same aroma compounds smell stronger in a weaker drink.
- Raises perceived body and viscosity, and above about 10% starts to read as heat rather than sweetness.
- Feeds the acetic acid bacteria that make vinegar, so the thing that protects the cider is also the substrate for the commonest fault in it.
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.
- warming
- faintly sweet
- full
- spirituous at high strength
Ethanol has no single perception threshold: it contributes at every concentration a cider reaches, and its effect shifts from sweetness and body at ordinary cider strengths to warmth and burn only in fortified and ice-concentrated products.
Descriptors it is responsible for
Sensory records that name Ethanol as a cause. Each states the perception and the mechanism behind it.
- Nail varnish — The sharp solvent lift of ethyl acetate above threshold, the commonest volatile fault-adjacent note in cider.
- Vinegar — Acetic acid from acetic acid bacteria oxidising ethanol in the presence of air — the classic cider spoilage.
- Drains — A heavy, stagnant, sewer-like note from mercaptans formed when hydrogen sulphide is left to react.
- Glue — Ethyl acetate at fault concentration, past the solvent stage and into adhesive.
- Mousy — A retronasal-only taint of mouse cage and stale grain, from tetrahydropyridines produced by lactic bacteria and Brettanomyces.
- Flat and lifeless — The absence of aroma and lift where both were intended — a fault defined by what is missing rather than present.
- Overripe apple — Heavy, faintly alcoholic fruit aroma from apples past the climacteric, where the fruit has begun fermenting on its own account.
- Spirit cask — Whisky, rum or brandy character carried into cider by a previously filled barrel, from residual spirit held in the staves.
- Toffee apple — Dense Maillard character — butter, brown sugar, slight roast — over concentrated apple, characteristic of ice cider and pommeau.
- Bletted pear — Deep, faintly winey overripe pear character from fruit softened past ripeness, met in traditional perry and in medlar-like notes.
- Fruit store — The close, sweet, faintly fermenting smell of a loft of apples held before milling, met in ciders made from sweated fruit.
- Ginger — Hot, citrus-edged spice from added ginger, distinguishable from alcohol warmth by its aromatic component.
- Plastic — A synthetic, hot-plastic or crayon note from packaging materials, hose or liner contact.
The structure it moves
| Dimension | What it is |
|---|---|
| Alcohol | The warming, slightly sweet presence of ethanol. |
| Body | How much weight and viscosity the drink has in the mouth. |
| Sweetness | How sweet the drink tastes, which is not the same as how much sugar it contains. |
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.
3 separate analyses of alcohol by volume. They are shown as they were measured, in their own contexts, and are not averaged — the same fruit grown somewhere else can genuinely give a different number.
Alcohol by volume1.2–8.5 % ABV
context not recorded · HM Revenue & Customs
A duty band, not a description of how cider tastes. UK excise treats a product above this strength as wine rather than cider, and the lower bound is the point at which a drink becomes dutiable at all. Plenty of cider made outside the UK sits above it.
Alcohol by volume4.0–8.5 % ABV
context not recorded · Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739
The range a fully fermented single-pressing juice reaches without addition, set by how much sugar the fruit carried. Ice ciders, fortified products and chaptalised ciders exceed it by design; low-alcohol products fall below it by removal or by arrested fermentation.
Alcohol by volume6.3–6.6 % ABV
Villaviciosa, Asturias, Spain, 2001–2002 · 4 samples · Analysis of finished sidra natural after spontaneous fermentation to dryness · Suárez Valles, Pando Bedriñana, Fernández Tascón, Querol Simón and Rodríguez Madrera, Food Microbiology 24(1):25–31
What Asturian musts of under 110 g/L sugar actually reach when fermented out with nothing added. The narrowness of the band across two harvests and two pressing technologies is the point: the strength of a sidra natural is set by the fruit, and there is no addition permitted that could move it.
Ethanol content of the finished drink. Measured in percent alcohol by volume.
Specific gravity1.040–1.065 SG
context not recorded · Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739
Juice density before fermentation, the practical proxy for how much alcohol the juice can make. Density falls below 1.000 at dryness because ethanol is lighter than water, which is why a dry cider reads around 0.995 rather than 1.000.
Juice density, the practical proxy for sugar before fermentation. Measured in specific gravity.
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.
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.
Sugar addition
Adding sugar or apple juice concentrate to raise potential alcohol before fermentation, and the regulatory and compositional consequences of doing so.
Fortification
Adding distilled spirit to juice or cider so that fermentation cannot proceed, the classic route to pommeau and a step that generally takes the product outside the legal category of cider.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
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.
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.
Acetification
The active conversion of a cider’s ethanol into acetic acid by acetic acid bacteria at an air interface — the process, running in the vessel, that produces volatile acidity.
Volatile acidity
The measurable fraction of acidity that can be steam-distilled off, dominated by acetic acid and read as vinegar sharpness in the nose and a hard, hot finish.
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.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
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.
Ethyl acetate taint
A solvent, nail-varnish or pear-drop aroma from ethyl acetate, the most abundant ester in cider and the one that turns from lift to fault over a narrow range.
Film yeast growth
A pale, powdery or wrinkled film of aerobic yeast growing on the surface of a standing cider, consuming alcohol and acid and producing acetaldehyde.
Mousiness
A retronasal taint of mouse cage, stale popcorn or crackers that appears only after swallowing — and that a substantial fraction of people cannot detect at all.
Vinegar fly contamination
Small flies carrying acetic acid bacteria and spoilage yeasts directly into juice and cider, and depositing them wherever they land.
Geranium taint
A sharp, unmistakable crushed-geranium-leaf smell produced when lactic acid bacteria metabolise sorbic acid added as a preservative.
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.
Thin body
A cider with no weight or texture in the mouth, most often from over-watered pomace, low-gravity juice or a blend with nothing to give it substance.
Framboise
A raspberry-and-rotten-fruit character with sulphurous overtones, produced by *Zymomonas mobilis* in sweet ciders that still contain sugar.
Sorbate off-flavour
A faint plastic, candle-wax or celery-like note from sorbic acid used as a preservative, distinct from the geranium taint that bacteria produce from it.
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 uvarum
A cold-tolerant relative of *S. cerevisiae* recovered from spontaneous cider and wine ferments, associated with low-temperature fermentation and higher glycerol.
Acetobacter aceti
An acetic acid bacterium that oxidises ethanol to acetic acid wherever cider meets air, and the organism behind most volatile acidity in cider.
Zygosaccharomyces bailii
A preservative-resistant spoilage yeast that refements sweetened cider and juice, and one of very few organisms able to grow through sorbate and benzoate at cider strength.
About Ethanol
Yeast converts one molecule of glucose or fructose into two of ethanol and two of carbon dioxide, extracting the energy it needs along the way. The arithmetic that follows from this is the most useful piece of cider mathematics there is: ethanol is lighter than water, so as sugar disappears the liquid gets less dense, and the fall in density tracks the alcohol produced. A hydrometer reading before and after fermentation therefore measures alcohol indirectly, using a conventional multiplier of roughly 131 applied to the drop in specific gravity. That multiplier is an approximation rather than a constant — it drifts with the starting gravity and with how much unfermentable material the juice carried — which is why careful producers treat a calculated ABV as a good estimate and a laboratory figure as the answer.
How much alcohol a cider ends at is decided almost entirely at the press, because apple juice is a fixed sugar solution and yeast will normally take all of it. Juice at 1.050 finishes near 7%; juice at 1.045 near 6.5%. This is why cider strength clusters where it does, and why the traditional ways of making a stronger or weaker drink are all ways of changing the sugar rather than the ferment: concentrating juice by freezing for ice cider, adding sugar where the law and the style allow it, or stopping the ferment early and keeping the sugar in the glass.
Ethanol does far more in the finished drink than register as strength. It changes how volatile everything else is: an ester sitting in 8% alcohol partitions into the headspace less readily than the same ester in 4%, so a low-alcohol cider can smell more strongly of fruit while tasting thinner. It contributes genuine mouthfeel — the fullness of a strong dry cider is largely ethanol, since there is no sugar left to provide it. And it is mildly sweet on the tongue in its own right, enough that a bone-dry cider at 8% reads less austere than a bone-dry cider at 4%.
The same molecule creates the risk. Acetic acid bacteria oxidise ethanol to acetic acid whenever they have air, so every cider is one bad seal away from the vinegar fault; and yeast under stress diverts part of the pathway, leaving acetaldehyde behind rather than reducing it fully to ethanol. Alcohol protects a cider against most bacteria and gives no protection at all against the two groups that use it as food. That is why keeping air away from a finished cider matters more, not less, once fermentation is complete.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Sugars
Glucose
The sugar yeast takes first and the smallest of the three in apple juice, which is why the last sugar left in a slow ferment is almost never glucose.
Sugars
Fructose
The dominant sugar of apple juice and the sweetest of the common sugars, which is why apple juice tastes sweeter than its total sugar figure implies and why a stuck ferment leaves sweetness behind.
Gases
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.
Alcohols
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.
Acids
Acetic acid
The vinegar acid, made by bacteria oxidising ethanol whenever air reaches a cider, and the one fault in cider that no later processing can undo.
Aldehydes
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.
Esters
Ethyl acetate
The most abundant ester in cider, giving lift and pear-drop at low concentration and nail varnish at high, and the earliest audible warning that acetic bacteria are at work.
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.
- 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.
- Why does my cider taste like vinegar — Acetic acid bacteria have reached the cider and, given air, are converting its alcohol into acetic acid. The cause is almost always oxygen — an unfilled vessel, a leaking bung, or a slow transfer.
- 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.
- Can you fix a cider that has gone vinegary — Not really. Volatile acidity cannot be removed at small scale, and blending it away only dilutes it. The realistic options are to accept it, to blend a lightly affected batch into a much larger sound one, or to let it finish becoming vinegar.
- How much acetic acid is normal in cider — A small amount is present in every cider and contributes lift. Sound Asturian sidra natural has been measured at 0.2 to 0.3 g/L, and a clean modern cider much above about 0.7 g/L is generally showing a fault rather than a style.
- Where does the fizz in cider come from — Either from fermentation trapped in a sealed container, or from carbon dioxide dissolved into the cider under pressure before filling. The French cider appellations permit only the first, and require at least 1.0 to 1.5 bar at 20 °C depending on the name.
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.
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.
Alcoholic Products Technical Guide, section 2 — alcoholic products (formerly Excise Notice 162)
HM Revenue & Customs · regulator · passage verified 2026-08-24
What may be called cider or perry for UK duty purposes. The substantive text now lives in section 2 of the Alcoholic Products Technical Guide rather than in the notice itself, and the passages below were read there. The widely repeated "35% juice" figure checks out — but note two things the figure alone hides: it is a tax threshold rather than a quality standard, and concentrate and dilution both count towards it.
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.