Organism
Clostridium species
Spore-forming anaerobic bacteria of soil and windfall fruit that cause butyric spoilage in low-acid products, and are essentially excluded from cider by its acidity.
- Kind
- Bacteria
- Binomial
- Clostridium spp.
- Role
- Spoilage
What it does
- Ferments sugars and organic acids anaerobically to butyric acid, hydrogen and carbon dioxide, producing the rancid, cheesy, vomit-like odour that characterises butyric spoilage.
- Forms heat-resistant endospores that survive pasteurisation regimes designed for vegetative organisms, so thermal processing is not by itself a control.
- Requires a comparatively high pH to germinate and grow, generally above pH 4.5 for the species of food-spoilage concern, which places cider well outside its range.
- Enters production on soil, on windfall fruit and on unwashed equipment, so its relevance to a cidery is a fruit-handling and hygiene matter rather than a fermentation one.
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 | Species of concern grow from roughly 10 °C to 50 °C depending on the organism; mesophilic species grow at ambient. |
| pH | The decisive constraint: growth generally requires above about pH 4.5, and cider at pH 3.2–3.9 is outside it. |
| Oxygen | Obligately anaerobic; oxygen is toxic to the vegetative cells. |
| Alcohol tolerance | Low; ethanol at cider strength is inhibitory. |
| Sulphite tolerance | Not the relevant control, since acidity already excludes the organisms. |
What it produces
Compounds this organism makes. Which organism made a compound usually decides whether it reads as a feature or as a symptom.
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.
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.
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.
Lactic off-flavours
Sauerkraut, sour milk, silage or cheesy notes from lactic acid bacteria working on sugars and other substrates rather than on malic acid alone.
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.
Where in the process it appears
Fruit washing
Removing soil, grass, stones and surface contamination from gathered fruit, usually in a water flume, before it reaches the mill.
Fruit sorting
Taking rotten, mouldy and damaged fruit and foreign material out of the crop before it reaches the mill, which is the primary control on patulin in cider.
Windfall management
Deciding which fruit that has reached the orchard floor can be used, and getting the rest out of the crop before it becomes a patulin problem.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Juice pasteurisation
Heat treatment of juice before fermentation, which inactivates enzymes and microorganisms, and in doing so removes the wild flora that would otherwise ferment it.
About Clostridium species
This record exists mainly to say clearly what Clostridium does not do in cider. The genus is a serious concern in low-acid canned and preserved foods, and it has a place in the general food-safety literature that makes people ask about it. In cider it is effectively excluded by pH: the species of food-spoilage and food-safety concern require an environment above roughly pH 4.5, and cider is typically between pH 3.2 and 3.9.
Where it becomes worth thinking about is at the fruit end. Windfall apples collected from wet ground carry soil, and soil is where clostridial spores live. That matters not because the spores will grow in the cider, but because fruit dirty enough to carry them is fruit dirty enough to carry rot organisms, patulin-producing moulds and Gluconobacter. The washing and sorting that keeps those out keeps this out too.
It is also worth naming a piece of folklore this record is positioned against: the occasional suggestion that home-fermented cider poses a botulism risk. The acidity that defines cider is precisely what makes that implausible, and CiderHQ states the mechanism — a pH limit on growth — rather than either amplifying or waving away the concern.
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 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.
- 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.
- Can you use windfall apples for cider — Traditional cider making relies on fruit gathered from the ground, and there is nothing wrong with it if it is sound. Rotten fruit is a different matter: brown rot carries patulin into the juice and should be discarded, not pressed.
- Will pasteurised apple juice ferment — Not on its own — pasteurisation kills the wild yeast — but it ferments readily once a cultured yeast is pitched.
- Are apples washed before making cider
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.
European Food Safety Authority scientific opinions
EFSA · regulator · retrieved 2026-08-24
Registered for the food-safety questions cider genuinely raises: patulin in juice from rotten fruit, sulphite sensitivity, and the toxicology behind additive limits.