Organism
Leuconostoc mesenteroides
A heterofermentative lactic acid bacterium common on fruit and early in fermentation, and a classic producer of the dextran that causes ropiness.
- Kind
- Bacteria
- Binomial
- Leuconostoc mesenteroides
- Role
- Malolactic conversion, Spoilage
What it does
- Synthesises dextran from sucrose using extracellular dextransucrase, producing the slimy, viscous texture known in cider as ropiness or oiliness.
- Ferments heterofermentatively, yielding lactic acid, acetic acid, ethanol, mannitol and carbon dioxide, so it raises volatile acidity wherever it grows on sugar.
- Converts malic acid to lactic acid, and is often part of the early lactic population in juice and young cider before more acid-tolerant species take over.
- Colonises early: it is common on fruit surfaces and in fresh juice, and is one of the first bacteria to grow if juice is held warm before fermentation.
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 | Grows across roughly 10 °C to 30 °C, with a preference for the middle of that range. |
| pH | Less acid-tolerant than *Oenococcus*, generally growing above about pH 3.5. |
| Oxygen | Facultatively anaerobic. |
| Alcohol tolerance | Low to moderate; it is displaced as ethanol rises and is largely an early-stage organism. |
| Sulphite tolerance | Sensitive; juice sulphiting suppresses it effectively. |
What it produces
Compounds this organism makes. Which organism made a compound usually decides whether it reads as a feature or as a symptom.
Lactic acid
The softer acid that replaces malic when malolactic fermentation runs, halving the acid a cider carries and changing its texture as much as its sharpness.
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.
Beta-glucan
The bacterial exopolysaccharide behind ropiness, which turns a cider oily and thread-like without changing how it smells or tastes.
Sorbitol
The unfermentable sugar alcohol that pears carry in quantity and apples carry only in trace, and the single reason a fully fermented perry keeps a sweetness a fully fermented cider cannot.
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
Ropiness
Cider that pours thick and pulls into an oily thread, caused by lactic acid bacteria secreting long-chain glucan polymers into the drink.
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.
Volatile acidity
The measurable fraction of acidity that can be steam-distilled off, dominated by acetic acid and read as vinegar sharpness in the nose and a hard, hot finish.
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
Juice storage
Holding unfermented juice sound between pressing and fermentation, by chilling, sulphiting, gas blanketing, freezing or aseptic filling.
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.
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
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.
Juice settling
Letting freshly pressed juice stand cold and undisturbed so that gross solids fall, then racking the cleaner juice off the deposit before pitching.
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.
About Leuconostoc mesenteroides
Leuconostoc mesenteroides is the lactic acid bacterium of the pre-ferment and the early ferment. It is abundant on plant surfaces, grows quickly, and is one of the organisms that gets going if juice is left standing warm between the press and the start of fermentation. As ethanol rises and pH falls it gives way to more tolerant species, so its window is short — but the damage it does in that window can be permanent.
Ropiness is the reason it is remembered. Given sucrose, the species produces dextran, a high-molecular-weight glucose polymer, and a cider carrying it pours in a viscous, oily stream rather than freely. The condition is disconcerting to look at and is a real quality defect, though it is worth saying plainly that it is a texture problem and not a safety one. Vigorous agitation, sulphiting and filtration can break the polymer up and remove the organism, with mixed success depending on how far it has gone.
Sucrose is the key. Apple juice contains relatively little of it compared with glucose and fructose, so the classic ropiness risk arrives with sugar addition — chaptalisation, priming, back-sweetening with sucrose — rather than from the fruit alone. That makes it a process risk a maker controls by choosing when and how sugar enters the cider, and by ensuring the cider is protected when it does.
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.
- Can you fix a cider that has gone vinegary — Not really. Volatile acidity cannot be removed at small scale, and blending it away only dilutes it. The realistic options are to accept it, to blend a lightly affected batch into a much larger sound one, or to let it finish becoming vinegar.
- 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.
- 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.
- 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 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.
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.