Organism
Komagataeibacter species
Highly acetic-acid-tolerant bacteria that build the cellulose pellicle known as mother of vinegar, and the organisms of industrial vinegar fermentation.
Also called Gluconacetobacter (in part), Acetobacter xylinum.
- Kind
- Bacteria
- Binomial
- Komagataeibacter spp.
- Role
- Spoilage, Surface film
What it does
- Synthesises extracellular bacterial cellulose, extruding glucose polymer chains that assemble into the tough, gelatinous mat called mother of vinegar — a structure that holds the population at the air-liquid interface where oxygen is.
- Oxidises ethanol to acetic acid like other acetic acid bacteria, but tolerates far higher acetic acid concentrations, which is why it dominates the late stages of vinegar fermentation.
- Persists in vinegar plants, in wooden vessels and in any cidery that also makes vinegar, and can be carried back into cider production on shared equipment.
- Forms a physical barrier as the pellicle thickens, complicating cleaning and protecting the population beneath from sanitisers.
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 20 °C to 35 °C, warmer than most cider cellars. |
| pH | Extremely acid-tolerant, remaining active at acetic acid concentrations that stop most organisms. |
| Oxygen | Obligately aerobic, and structurally organised around reaching air. |
| Alcohol tolerance | Tolerates cider strength and beyond. |
| Sulphite tolerance | Not reliably controlled by sulphite once an established pellicle is present. |
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.
Beta-glucan
The bacterial exopolysaccharide behind ropiness, which turns a cider oily and thread-like without changing how it smells or tastes.
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.
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
Acetification
The active conversion of a cider’s ethanol into acetic acid by acetic acid bacteria at an air interface — the process, running in the vessel, that produces volatile acidity.
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.
Excessive sediment
More deposit in the bottle or vessel than the presentation intends, ranging from a normal conditioning yeast layer to a loose sludge that clouds every pour.
Vinegar fly contamination
Small flies carrying acetic acid bacteria and spoilage yeasts directly into juice and cider, and depositing them wherever they land.
Where in the process it appears
Sanitation
The cleaning and sanitising discipline that underlies every other process, and why removing soil must come before any attempt to kill organisms.
Fermentation vessels
The container a cider ferments in — wood, stainless, plastic, glass or concrete — and how its permeability, thermal mass and resident microflora shape the result.
Barrel ageing
Holding cider in wood — which may mean an old neutral vat used simply as a vessel, or fresh or spirit-seasoned oak used as a source of flavour, and the two are not the same operation.
Topping up
Refilling a maturing vessel as evaporation and racking losses lower the level, so that no significant surface of cider is ever left in contact with air.
Cellar storage
Holding packaged cider in conditions that let it change slowly and predictably, where stability of temperature matters more than the temperature itself.
About Komagataeibacter species
The genus name is recent and the reclassification is worth stating. Cellulose-producing acetic acid bacteria were long placed in Acetobacter — Acetobacter xylinum is the name in most older writing — then moved to Gluconacetobacter, then split again in 2012 with the acetic-acid-tolerant, vinegar-associated species placed in the new genus Komagataeibacter. Three names, one group of organisms, and all three still in circulation.
What sets them apart functionally is cellulose. The pellicle is not incidental: it is a structure that keeps an obligately aerobic organism at the surface where oxygen is, and it is the physical basis of the mother of vinegar that anyone who has kept a vinegar crock has seen. Their tolerance of high acetic acid concentration means they take over the late stages of a vinegar fermentation that Acetobacter began.
For a cider maker, the significance is largely one of cross-contamination and cleaning. A cidery that also makes vinegar has a reservoir of highly acid-tolerant acetic acid bacteria on the premises, and a cellulose mat in a vessel or a line is difficult to remove and shelters the organisms underneath it from sanitiser contact. Separating vinegar production from cider production in space and in equipment is the standard response.
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.
- Why does my cider taste like vinegar — Acetic acid bacteria have reached the cider and, given air, are converting its alcohol into acetic acid. The cause is almost always oxygen — an unfilled vessel, a leaking bung, or a slow transfer.
- 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.
- How should i store cider — Cool, dark and at a steady temperature. Light causes light-strike in clear glass, warmth accelerates oxidation, and temperature swings push cider past the closure of a bottle that is not tightly sealed.
- What should i ferment cider in — Anything inert, cleanable and closable: glass demijohns, food-grade plastic, stainless steel, or a wooden cask if you can keep it sound. Vessel shape and material change how much oxygen the cider sees and how fast it clears.
- Why is there sediment in the bottom of my cider bottle — In a bottle-conditioned cider the sediment is yeast and is expected — pour carefully and leave the last centimetre. In a filtered cider it means something has grown since bottling.
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.