Compound
Potassium sorbate
The soluble salt in which sorbic acid is actually added, used to hold sweetness in a bottled cider, and dangerous to use without sulphite because of what lactic bacteria do to it.
- Class
- Additives and processing aids
- Formula
- C6H7KO2
- How often it matters
- Regularly encountered
What it does in cider
- Dissolves readily where sorbic acid itself does not, which is why it is the practical form for addition.
- Dissociates in the cider to give sorbic acid, of which only the undissociated fraction inhibits yeast.
- Prevents renewed yeast growth in a back-sweetened cider but does not stop a fermentation already under way.
- Requires adequate free sulphur dioxide alongside, because lactic acid bacteria convert sorbic acid to the compound responsible for the geranium fault.
How it is perceived
What the compound registers as, and at roughly what concentration. Perception is not a property of the molecule alone: sugar, tannin and carbonation all change where a threshold falls.
- neutral at working concentrations
- crushed geranium leaf where bacterial conversion has occurred
The geranium compound is perceptible at extremely low concentration and is not removable, so the failure mode of a sorbate addition is far more damaging than the addition is beneficial.
Descriptors it is responsible for
Sensory records that name Potassium sorbate as a cause. Each states the perception and the mechanism behind it.
- Geranium — The crushed-geranium-leaf note produced when lactic bacteria metabolise added sorbate — a fault with one cause and no remedy.
The structure it moves
| Dimension | What it is |
|---|---|
| Fermentation character | Aromas made by the ferment rather than carried in from the fruit. |
What forms it
Processes that put this compound into the drink, or increase how much of it is there.
Sorbate stabilisation
Adding potassium sorbate to prevent yeast from restarting a fermentation in the package — an inhibitor rather than a killer, and one that must never be used without sulphite.
Back-sweetening
Adding sugar, juice or concentrate to a cider that has fermented dry — a straightforward adjustment that leaves the drink microbiologically unstable until something is done about it.
Bottling
Transferring finished cider into glass, where the dominant variable is how much oxygen the liquid picks up in the few seconds it takes to fill and close each bottle.
Faults it is implicated in
Being implicated is not the same as being a fault. Several of the compounds on this site are ordinary constituents of a sound cider and define a named fault only above a concentration.
Geranium taint
A sharp, unmistakable crushed-geranium-leaf smell produced when lactic acid bacteria metabolise sorbic acid added as a preservative.
Sorbate off-flavour
A faint plastic, candle-wax or celery-like note from sorbic acid used as a preservative, distinct from the geranium taint that bacteria produce from it.
Unwanted refermentation
Fermentation restarting in a sealed container, generating carbon dioxide that was not planned for and pressure that a bottle may not withstand.
Bottle over-carbonation
More dissolved carbon dioxide in the bottle than intended or than the glass is rated for — a presentation problem at the mild end and a physical hazard at the severe one.
Excess sulphur dioxide
A struck-match or burnt-match aroma and a prickle at the back of the nose from too much free sulphur dioxide, with a real health consideration for sulphite-sensitive people.
Organisms that produce it
Which organism is responsible usually decides whether the compound is a feature or a symptom.
Saccharomyces cerevisiae
The yeast that finishes essentially every cider, whether it arrives in a sachet or from the fruit, the press and the vessel.
Zygosaccharomyces bailii
A preservative-resistant spoilage yeast that refements sweetened cider and juice, and one of very few organisms able to grow through sorbate and benzoate at cider strength.
Lactiplantibacillus plantarum
A versatile lactic acid bacterium, renamed out of *Lactobacillus* in 2020, capable of malolactic conversion and of a range of faults depending on conditions.
Oenococcus oeni
The acid-tolerant lactic acid bacterium that carries out most deliberate malolactic fermentation, converting malic acid to lactic acid after the yeast has finished.
About Potassium sorbate
Sorbic acid is barely soluble in water, so it is added as its potassium salt, which is very soluble. Once in the cider the salt dissociates and an equilibrium establishes between sorbate ion and sorbic acid, with only the undissociated acid able to enter a yeast cell and interfere with it. Everything about dosing therefore depends on pH, in the same way it does for sulphur dioxide, though sorbic acid’s higher dissociation constant makes it more forgiving across the range cider occupies.
What it is for is narrow and worth stating precisely: it prevents yeast from growing again in a cider that has been sweetened and packaged. It will not stop an active fermentation, it will not kill an established population, and it does nothing about bacteria. A producer using it must first have a cider that is genuinely finished, and must remove or reduce the yeast population by racking, fining or filtration before adding it.
The reason it is never used alone is the geranium fault. Lactic acid bacteria reduce sorbic acid to sorbyl alcohol, which rearranges under acid conditions to 2-ethoxyhexa-3,5-diene — a compound that smells of crushed geranium leaf, is detectable at vanishingly small concentrations, and cannot be removed. Adequate free sulphur dioxide suppresses the bacteria and prevents the sequence, which is why sorbate and sulphite are always discussed as a pair. Permitted maximum concentrations are set by food additive law in each jurisdiction.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Additives and processing aids
Sorbic acid
A preservative that stops yeast but not bacteria, and whose effectiveness — like that of sulphur dioxide — depends on pH, because only the undissociated molecule works.
Additives and processing aids
Sulphur dioxide
The antimicrobial and antioxidant on which most modern cidermaking depends, and whose effectiveness collapses as pH rises — which makes every sulphiting decision a pH decision first.
Additives and processing aids
Benzoic acid
A weak-acid preservative added as sodium benzoate, more useful the lower the pH, and encountered in cider mainly in low-alcohol and soft products rather than in traditional ones.
Sugars
Fructose
The dominant sugar of apple juice and the sweetest of the common sugars, which is why apple juice tastes sweeter than its total sugar figure implies and why a stuck ferment leaves sweetness behind.
Acids
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.
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.
- Does cider contain sulphites — Most does. Sulphur dioxide is added to protect juice and finished cider, and fermentation itself produces a small amount even when none is added. European labels must declare it above 10 mg per litre.
- Why did my cider bottles explode — Because fermentable sugar was still present, or too much priming sugar was used, and the pressure exceeded what the bottle could hold. Never bottle a cider whose gravity is still falling, and never use bottles not designed for pressure.
- Which yeast ferments cider — Saccharomyces cerevisiae finishes almost every cider fermentation, whether it was pitched or arrived from the press house. In a spontaneous ferment it is not the first organism present, only the one that survives the alcohol it makes.
- Which sugar is most of the sugar in apple juice — Fructose, by a long way. Apple juice carries roughly twice as much fructose as glucose, with a smaller amount of sucrose, and fructose is the sweetest of the three on the tongue.
- 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 cider contain lactic acid — Because malolactic bacteria converted the malic acid into it. Malic acid has two acid groups and lactic acid has one, so roughly half the titratable acidity disappears and the cider tastes softer.
Where to go next
- All compounds — Grouped by what the fruit brings and what the ferment makes of it.
- Sensory — Every descriptor, with the compound or process that causes it.
- Microbiology — The organisms whose metabolism most of this chemistry belongs to.
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.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
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.
Codex Alimentarius food standards
FAO / WHO · standards body · retrieved 2026-08-24