Compound
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.
Also called Phenylethyl alcohol, Rose alcohol.
- Class
- Alcohols
- Formula
- C8H10O
- How often it matters
- Occasional
What it does in cider
- Arises when yeast deaminates phenylalanine and reduces the remainder, so it appears in ferments rather than in juice.
- Supplies a rose-and-honey aroma that persists through maturation better than most fruit esters, because it is an alcohol rather than an ester and is not lost to hydrolysis.
- Converts in part to 2-phenylethyl acetate, which shifts the same character towards rose petal and honey.
- Rises with certain non-Saccharomyces yeasts, which is one reason spontaneous ferments often carry more floral character than inoculated ones.
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.
- rose
- honey
- blossom
- lilac
Among the higher alcohols it is one of the few whose own aroma is clearly identifiable in finished cider rather than merging into a general fusel impression.
Descriptors it is responsible for
Sensory records that name 2-Phenylethanol as a cause. Each states the perception and the mechanism behind it.
- Apple blossom — A light, sweet floral note from terpene alcohols and 2-phenylethanol, distinct from the fruit character of the same tree.
- Honey — A sweet, waxy floral note from phenylacetaldehyde, formed by mild oxidation of 2-phenylethanol as cider ages.
- Bubblegum — A confected tropical note from acetate esters at high concentration with 2-phenylethanol behind them.
- Fusel — A hot, heavy, spirituous impression from elevated higher alcohols, felt as warmth as much as smelled.
- Rose — The rose-petal note of 2-phenylethanol, a higher alcohol produced by yeast from phenylalanine.
- Hawthorn — A heavy, faintly fishy hedgerow-blossom note from trimethylamine and phenylacetaldehyde in ageing cider.
- Honeycomb — Honey with a caramelised, slightly burnt-sugar edge, met where oxidative honey notes coincide with Maillard character.
- Nectar — A light, sweet, floral-sugary impression from phenylethyl acetate and residual sugar together.
The structure it moves
| Dimension | What it is |
|---|---|
| Fermentation character | Aromas made by the ferment rather than carried in from the fruit. |
| Fruit character | How strongly the drink smells of apple or pear, and of fruit generally. |
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.
2-Phenylethanol45.0–121.0 mg/L
Villaviciosa, Asturias, Spain, 2001–2002 · 4 samples · Gas chromatography with flame ionisation detection · Suárez Valles, Pando Bedriñana, Fernández Tascón, Querol Simón and Rodríguez Madrera, Food Microbiology 24(1):25–31
The spread inside one cellar across two harvests is nearly threefold, which is a useful warning about single figures for aroma compounds. Pneumatic pressing gave the higher values in both years.
The rose-scented higher alcohol, made from phenylalanine and one of the few aroma compounds in cider present far above its own threshold. Measured in milligrams per litre.
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.
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.
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.
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.
Torulaspora delbrueckii
A non-Saccharomyces yeast that ferments further than most of its early-succession neighbours while producing notably little acetic acid.
Metschnikowia pulcherrima
An early-succession yeast that suppresses competitors by locking up iron, and is used commercially as a controlled non-Saccharomyces partner rather than as a fermenter.
Wickerhamomyces anomalus
A tolerant, ester-heavy yeast common in fruit and juice, notable both as a producer of ethyl acetate and as a source of antimicrobial killer toxins.
About 2-Phenylethanol
Floral aroma in cider is often assumed to come from the blossom or the fruit, and mostly it does not. The rose note is 2-phenylethanol, and it is made during fermentation from phenylalanine by the same Ehrlich route that gives every other fusel alcohol. It can also be built from scratch by the yeast when phenylalanine runs short, which is why it appears even in juices with a thin amino acid profile.
It is unusually durable. Fruit esters hydrolyse steadily in the bottle and a cider’s fresh-apple aroma fades within a year or two; 2-phenylethanol does not, so the floral and honeyed impression of an older cider often becomes more prominent simply because everything around it has receded. Some of it esterifies to 2-phenylethyl acetate during and after fermentation, moving the note towards honey and rose petal.
Strain choice moves it a long way. Several non-Saccharomyces yeasts common in spontaneous cider ferments — Torulaspora delbrueckii and Metschnikowia pulcherrima among them — are notably better producers than most cultured Saccharomyces, which is part of why wild-fermented ciders are so often described as more floral, and part of the argument for co-inoculation in ciders that are otherwise clean.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
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.
Nitrogen compounds
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.
Phenolics
Terpenes
The floral and citrus aroma compounds that apples carry only in traces and that hops, spices and botanicals bring in quantity, which is why a hopped cider smells so different from an unhopped one.
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.
- 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 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.
- What are fusel alcohols in cider — They are the higher alcohols yeast makes from amino acids rather than from sugar, mostly amyl alcohols. They carry weight and warmth of aroma, and in Asturian cider they run to a couple of hundred milligrams per litre.
- What does metschnikowia do in a cider ferment — It locks iron out of solution as the red pigment pulcherrimin, which inhibits organisms that need iron. That is a defined antimicrobial mechanism rather than simple competition, and it is why the species is sold for sequential inoculation.
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.