Organism
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.
Also called Pichia anomala, Hansenula anomala, Candida pelliculosa.
- Kind
- Yeast
- Binomial
- Wickerhamomyces anomalus
- Role
- Primary fermentation, Surface film, Spoilage
What it does
- Synthesises ethyl acetate in quantities high even by non-Saccharomyces standards, making it a frequent contributor to solvent character in juice and in the early ferment.
- Secretes killer toxins — glucanase-type proteins that damage the cell walls of sensitive yeasts — giving it a direct antagonistic mechanism against competitors and a research interest as a biocontrol agent.
- Grows across an unusually wide range of pH, temperature, oxygen availability and water activity, which is why it turns up in juice, on fruit, in silage and in stored grain alike.
- Forms films on the surface of stored juice and of ullaged cider, oxidising ethanol like other film yeasts.
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 | Very broad, roughly 5–37 °C. |
| pH | Grows from around pH 2 to pH 12 in laboratory conditions — a range no other yeast in this file approaches — and is entirely untroubled by cider acidity. |
| Oxygen | Facultative, and unusual in growing well at very low oxygen tension as well as at the surface. |
| Alcohol tolerance | High for a non-Saccharomyces yeast, generally reported to around 10–13% ABV. |
| Sulphite tolerance | Moderate; suppressed by sulphiting but more resistant than apiculate yeasts. |
What it produces
Compounds this organism makes. Which organism made a compound usually decides whether it reads as a feature or as a symptom.
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.
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.
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.
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
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.
Microbial haze
Cloudiness caused by a growing population of spoilage organisms, and therefore a symptom of something worse rather than a clarity problem in itself.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Where in the process it appears
Juice storage
Holding unfermented juice sound between pressing and fermentation, by chilling, sulphiting, gas blanketing, freezing or aseptic filling.
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.
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.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
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.
About Wickerhamomyces anomalus
This yeast has been renamed more than most, and the aliases are worth carrying: Hansenula anomala, then Pichia anomala, and in its anamorphic guise Candida pelliculosa, before molecular work placed it in Wickerhamomyces. A cider maker reading across sources from different decades will meet all four names for one organism.
Its cider relevance is double-edged in an interesting way. On the debit side it is among the most prolific producers of ethyl acetate in the yeast world, so where it is abundant in stored juice or in a slow-starting ferment, solvent character follows. On the credit side it secretes killer toxins that lyse other yeasts, and has been investigated as a biological control agent against post-harvest fruit moulds — including the Penicillium and Botrytis rots that concern any cidery storing fruit before milling.
It also demonstrates something worth stating about tolerance generally. The pH range over which this species will grow in the laboratory is extraordinarily wide, and that is a reminder that acidity alone protects a cider far less than makers sometimes assume. What actually keeps most organisms out of cider is the combination of low pH, ethanol, absence of oxygen and sulphite — no single one of them.
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.
- How do i sterilise cider bottles — Wash them clean first, then sanitise with a no-rinse sanitiser or a sulphite solution, and fill while still wet with it. Bottles that look clean but have dried deposits inside are the usual source of bottle spoilage.
- Why did my sweetened cider start fermenting again — Live yeast met the sugar that was added back. Sweetening is only stable if the yeast has been removed by sterile filtration, killed by pasteurisation, or held in check by sorbate together with sufficient sulphite.
- Why does my cider smell like nail varnish — That is ethyl acetate, formed when acetic acid combines with ethanol. In small amounts it reads as pear drops; above threshold it smells of solvent or nail varnish remover and usually accompanies rising volatile acidity.
- Why is sulphite added to cider — Sulphur dioxide suppresses spoilage bacteria and wild yeast before fermentation and protects the finished cider from oxidation. How much of it is active depends strongly on pH, which is why low-acid juice is harder to protect.
- How many calories are in cider — Roughly 40 to 60 kcal per 100 ml for most ciders, so a UK pint falls somewhere around 200 to 250 kcal. Alcohol contributes about 7 kcal per gram and residual sugar about 4, so both strength and sweetness matter.
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.
Hochschule Geisenheim University — beverage technology
Hochschule Geisenheim · university · retrieved 2026-08-24
German beverage-technology research covering apple wine and fruit juice processing, including the enzymology of clarification.