Compound
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.
Also called Hexa-2,4-dienoic acid.
- Class
- Additives and processing aids
- Formula
- C6H8O2
- How often it matters
- Regularly encountered
What it does in cider
- Inhibits yeast growth and reproduction, which is what makes it useful for holding residual sugar in a sweetened cider.
- Acts only in its undissociated form, so its potency falls as pH rises; with a pKa near 4.8, a substantial fraction is active across the pH range cider occupies, but a high-pH cider still gets less benefit than a low-pH one.
- Does not kill yeast already fermenting, so it is a preventive for a stabilised cider rather than a way of stopping an active ferment.
- Has essentially no effect on lactic acid bacteria, which is why it must never be used without adequate sulphur dioxide alongside it.
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
- faint plastic or waxy note at high addition
Sorbic acid itself is largely tasteless in cider at permitted levels. What is tasted is the geranium compound formed when lactic bacteria metabolise it, which is perceptible at extremely low concentration.
Descriptors it is responsible for
Sensory records that name Sorbic acid 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.
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.
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.
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.
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.
About Sorbic acid
Sorbic acid belongs to the same family of weak-acid preservatives as sulphur dioxide and benzoic acid, and it works the same way. The undissociated molecule is uncharged and lipid-soluble, so it crosses the cell membrane freely; inside, at the higher internal pH, it dissociates and acidifies the cytoplasm, and the cell spends its energy pumping protons back out instead of growing. Charged sorbate ions cannot cross the membrane and do nothing. This is why every weak-acid preservative is a pH-dependent preservative.
Sorbic acid’s dissociation constant is high enough — a pKa around 4.8 — that a useful fraction remains undissociated at any pH a cider reaches, which makes it more forgiving than sulphur dioxide in a high-pH cider. Its limitation is a different one: it acts on yeasts and moulds and barely troubles lactic acid bacteria at all.
That gap is not merely a shortfall in protection; it is an active hazard. Lactic acid bacteria can reduce sorbic acid and the product rearranges to 2-ethoxyhexa-3,5-diene, which smells intensely of crushed geranium leaf and is detectable at concentrations so low that the affected cider is unsaleable. Sorbate is therefore only ever used alongside enough free sulphur dioxide to suppress the bacteria, and permitted concentrations are set by food additive law in each jurisdiction rather than by the maker.
Related compounds
Compounds it is formed from, converted into, confused with, or routinely met alongside.
Additives and processing aids
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.
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.
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.
- 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.
- 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.
- Which bacterium carries out malolactic fermentation in cider — Oenococcus oeni, in cider as in wine. Genome studies find that the cider strains are genetically distinguishable from the wine ones and that the strain most basal to the whole species was isolated from cider.
- How do i sweeten cider without it fermenting again — Either remove or kill the yeast — sterile filtration or pasteurisation — or use a non-fermentable sweetener. Sorbate alone is not enough: it prevents yeast multiplying but does not kill what is already there, and needs sulphite alongside it.
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.
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.
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.
Codex Alimentarius food standards
FAO / WHO · standards body · retrieved 2026-08-24