Compound
Isoamyl acetate
The banana and pear-drop ester, made by yeast from isoamyl alcohol, and one of the clearest chemical signatures of a warm fermentation.
Also called 3-methylbutyl acetate, Banana ester.
- Class
- Esters
- Formula
- C7H14O2
- How often it matters
- Regularly encountered
What it does in cider
- Is assembled by yeast alcohol acetyltransferase from isoamyl alcohol and acetyl-CoA during active fermentation.
- Rises sharply with fermentation temperature and falls with must aeration, making it a direct readout of how the ferment was run.
- Is perceptible at concentrations roughly a thousand times lower than its parent alcohol, so small changes in production have large sensory effects.
- Hydrolyses steadily in the bottle, so the banana note of a young cider fades within the first year or two.
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.
- banana
- pear drop
- boiled sweets
- juicy fruit
Detected in the region of a few tens of micrograms per litre — low enough that it is present above threshold in most ciders and dominant in warm-fermented ones.
Descriptors it is responsible for
Sensory records that name Isoamyl acetate as a cause. Each states the perception and the mechanism behind it.
- Pear drop — The sweet-shop confectionery note of isoamyl acetate with ethyl acetate behind it — a fermentation product, not a pear one.
- Ripe apple — Full orchard-apple aroma from the acetate esters an apple accumulates through ripening and carries into the finished drink.
- Banana — Isoamyl acetate at high concentration — the same molecule as pear drop, in different company and at a different level.
- Sweet apple — An impression of sweet fruit produced by aroma rather than by sugar, common in dry ciders with a high ester load and low acidity.
- Bubblegum — A confected tropical note from acetate esters at high concentration with 2-phenylethanol behind them.
- Nectar — A light, sweet, floral-sugary impression from phenylethyl acetate and residual sugar together.
The structure it moves
| Dimension | What it is |
|---|---|
| Fruit character | How strongly the drink smells of apple or pear, and of fruit generally. |
| Fermentation character | Aromas made by the ferment rather than carried in from the fruit. |
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
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.
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.
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.
What removes or limits it
Processes that reduce it, hold it below a threshold, or stop it forming in the first place.
Bottle maturation
What happens to a cider after it is sealed in glass — which for most ciders is slow decline rather than improvement, and saying so is more useful than implying otherwise.
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.
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.
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.
Hanseniaspora valbyensis
The apiculate yeast most consistently reported as dominating the first days of a spontaneous cider fermentation, and a major contributor to its aroma.
Torulaspora delbrueckii
A non-Saccharomyces yeast that ferments further than most of its early-succession neighbours while producing notably little acetic acid.
About Isoamyl acetate
The banana note in a cider is one molecule, and it is not in the fruit. Yeast makes isoamyl acetate by joining isoamyl alcohol to an acetyl group, using an enzyme whose activity is strongly affected by temperature and by the presence of oxygen and unsaturated fatty acids. A ferment run warm, in a juice with little oxygen exposure, makes a lot of it; the same juice fermented cool with the same yeast makes markedly less.
Because the ester is perceptible at roughly a thousandth of the concentration its parent alcohol needs, the practical consequence of moving a fermentation from 12 °C to 20 °C is out of proportion to the chemistry involved. This is the single most reliable lever a cidermaker has over fruit-estery character, and it is available to anyone who can control tank temperature.
It is also transient. Ester formation and ester hydrolysis are the same reaction run in opposite directions, and in a finished cider the equilibrium favours hydrolysis. A cider that smelled emphatically of banana at bottling will not smell of it three years later, and this is a normal part of ageing rather than a failure of the bottle.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Alcohols
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.
Alcohols
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.
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.
Esters
Hexyl acetate
The apple-skin and pear ester that is genuinely carried in from the fruit rather than made by the yeast, and one of the few fresh-fruit aromas that survives fermentation.
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.
- 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.
- Why does my cider smell of nail varnish or solvent — Almost always ethyl acetate, the ester of acetic acid and ethanol. It is made by stressed yeast and by acetic acid bacteria, and it is perceptible at a small fraction of the concentration the acid itself needs, so it usually announces a problem before the vinegar does.
- 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.
- 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.
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.
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.
Washington State University cider research programme
Washington State University Northwestern Washington Research and Extension Center · university · passage verified 2026-08-24
The single most useful open cider dataset CiderHQ has found. The programme’s cultivar performance database gives juice chemistry, orchard behaviour, bloom and harvest timing and cider-maker tasting notes for 73 cultivars grown at one maritime site over fifteen years, and — unusually — publishes its classification thresholds alongside its figures, so the classification can be checked rather than taken on trust. It also states outright that its results diverge from the English ones. Read in full on 2026-08-24 and transcribed into `data/trials/wsu-mount-vernon.ts`; four published figures were found to be impossible and are withheld there with their reasons.