Organism
Schizosaccharomyces pombe
A fission yeast that degrades malic acid to ethanol rather than to lactic acid, offering deacidification without bacteria at the cost of a real risk of off-flavours.
Also called fission yeast.
- Kind
- Yeast
- Binomial
- Schizosaccharomyces pombe
- Role
- Primary fermentation, Spoilage
What it does
- Transports malic acid actively into the cell and decarboxylates it through the malic enzyme to pyruvate, which then goes to ethanol and carbon dioxide — maloalcoholic fermentation, as against the malolactic conversion carried out by bacteria.
- Removes malic acid essentially completely rather than converting it to a weaker acid, so the deacidification it achieves is larger than malolactic fermentation delivers.
- Ferments sugar to ethanol as well, so it can conduct a primary fermentation, though it is not usually asked to.
- Produces elevated acetaldehyde, hydrogen sulphide and higher alcohols in many reported trials, which is the standing objection to its use.
- Divides by binary fission rather than budding, producing distinctive rod-shaped cells.
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 | Prefers warmer conditions than most cider yeasts, growing well from roughly 20 °C to 32 °C. |
| pH | Tolerates low pH and remains active through the cider range. |
| Oxygen | Facultative; ferments anaerobically. |
| Alcohol tolerance | Moderate, commonly reported around 9–12% ABV. |
| Sulphite tolerance | Relatively tolerant, comparable with *Saccharomyces*. |
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.
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.
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.
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.
Low acidity
A cider without enough acid to give it definition, tasting soft, heavy and dull — and sitting at a pH that leaves it exposed to spoilage organisms.
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.
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.
Where in the process it appears
Acid adjustment
Correcting the acidity of low-acid juice before fermentation, usually with malic acid, and the difference between the pH question and the titratable acidity question.
Malolactic fermentation
A bacterial conversion of sharp malic acid into softer lactic acid, which lowers acidity, changes aroma, and in most traditional cider happens whether it was planned or not.
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.
Fermentation monitoring
Watching a running ferment through gravity, temperature, smell and surface behaviour, and reading the rate of change rather than any single figure.
About Schizosaccharomyces pombe
Schizosaccharomyces pombe is the answer to a specific question: how to lower the acidity of a very sharp juice without inviting lactic acid bacteria into the cellar. Where Oenococcus converts malic acid to lactic acid — trading a stronger diprotic acid for a weaker monoprotic one — S. pombe decarboxylates malate to pyruvate and takes it on to ethanol and carbon dioxide. The acid is not softened; it is removed.
For juice from a cold, wet season in a high-acid orchard that is genuinely attractive, and the species has been trialled for it in both wine and cider. The persistent difficulty is sensory. Reported trials frequently show raised acetaldehyde, hydrogen sulphide and higher alcohols, and a cider deacidified this way can arrive smelling of the treatment. Encapsulated and sequential-inoculation approaches exist to limit contact time for exactly this reason.
It is also a spoilage organism in the ordinary sense. A fission yeast growing uninvited in a low-acid cider will strip malic acid, flattening the drink and raising the pH into a range where bacterial spoilage becomes easier — the same chemistry, in a cider that did not want it.
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 long does cider take to ferment — A warm ferment with cultured yeast can finish in one to two weeks; a cool wild ferment in a cellar may take three months or more. Slow is not the same as stuck — the test is whether gravity is still falling.
- 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.
- 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.
- What is malolactic fermentation — Malolactic fermentation is a bacterial conversion of sharp malic acid into softer lactic acid, releasing carbon dioxide. It lowers total acidity and raises pH, and in cider it is often the source of a farmyard or buttery note as well.
- 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.
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.