Fault
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.
Also called over-sulphited, burnt match character.
Sulphites cause genuine reactions in a minority of people, particularly some people with asthma, and this is why the presence of sulphites above a defined threshold must be declared on labels in the UK and EU. Anyone giving cider to other people should assume some of them are sensitive and should say whether sulphite has been used. Handle the powder itself with care: potassium metabisulphite releases sulphur dioxide gas, which is an irritant to eyes and airways, so weigh and dissolve it in a ventilated space and not with your face over the container. Legal maxima for sulphur dioxide in cider are set nationally; work from the limit that applies where the cider is made rather than from any figure quoted in a book.
- Severity
- Serious — the batch may not be salvageable
- Where it starts
- Stabilisation, Juice treatment, Packaging
- Can it be fixed?
- Partly — it can be reduced, not removed
- When you notice it
- Juice treatment, Stabilisation, Packaging
- Signs
- 5 recorded
What it is
Sulphur dioxide is the principal preservative used in cider, valued because it inhibits spoilage organisms, inhibits polyphenol oxidase and scavenges oxygen. At normal working concentrations it is not perceptible. Above them it announces itself: a burnt-match smell, a sharp prickle high in the nose, a suppressed and slightly stripped flavour, and in some people a genuine physiological reaction. It is one of very few faults that comes entirely from something the maker chose to add.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
On the nose
- A burnt or struck match smell as the glass is raised
- A sharp prickle or sting high in the nose, felt rather than smelled — This is a trigeminal irritant response, which is why it feels physical rather than aromatic.
- Fruit aroma that seems suppressed or flattened rather than absent
On the palate
- A hard, slightly chemical bitterness in the finish
How the batch behaves
- A cough or tightness in the chest on smelling the glass, in a susceptible person
The words for it: Struck match. Each links to what produces it.
When it appears. Immediately after an addition, and it does diminish with time as the sulphite binds and dissipates. A struck-match note in a cider that has not been sulphited recently is more likely to be reduction.
Individual sensitivity varies widely, and a proportion of the population reacts to sulphites at ordinary levels for reasons unconnected to smell. Sulphur dioxide above the labelling threshold must be declared as an allergen on anything sold, which is a regulatory fact rather than a sensory one.
What it is mistaken for, and how to tell
One observation per rival, chosen because it separates them rather than because it describes either. Several of these are not faults at all — a style feature, a normal outcome, or the fruit behaving as it does.
- Reduction — Both read as struck match. Sulphur dioxide prickles the back of the nose and makes the eyes water at strength; reduction is flinty and lifts on aeration. Ask what was added and when.
- Hydrogen sulphide — Sharp and prickling rather than putrid. Rotten egg is not sulphur dioxide.
- Acetaldehyde excess — The two mask each other, because sulphur dioxide binds acetaldehyde. A cider that smells of both often has neither free: the sulphite has been spent.
What is actually happening
The chemistry or microbiology behind it. Understanding the mechanism is what makes the prevention make sense rather than being a list of rules.
In solution, sulphur dioxide exists in equilibrium between molecular sulphur dioxide, bisulphite and sulphite ions, and the proportion in each form is set by pH. Only the molecular form is meaningfully antimicrobial and only it is volatile enough to be smelled, and its share rises sharply as pH falls. The consequence is that the same addition to two ciders of different pH produces very different effects, both in preservation and in perceptibility.
Free sulphur dioxide is what is available to work. Bound sulphur dioxide is what has already reacted with carbonyl compounds — above all acetaldehyde, but also pyruvate, ketoglutarate and residual sugars — to form stable hydroxysulphonate adducts. Bound sulphite neither preserves nor smells. A cider that has been oxidised binds a large proportion of any addition almost at once.
This creates the classic route to over-sulphiting. A maker adds sulphite, measures free sulphur dioxide, finds it low because it has bound, adds more, and repeats. Total sulphur dioxide climbs while free sulphur dioxide appears stubborn, and the cider ends up carrying far more than intended.
The health question is real and specific. A minority of people, notably some with asthma, react to sulphites, and this is why declaration of sulphites above a defined threshold is a labelling requirement in the EU and UK under the food information regulation. That is a labelling rule about the presence of sulphites, not a statement that ordinary levels are hazardous to the general population.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Repeated additions chasing a free sulphur dioxide reading that keeps falling because the cider is oxidised | Stabilisation | common |
| Dosing by volume of vessel rather than by measured pHThe effective concentration depends on pH, so a single remembered rate is wrong for most juices. | Juice treatment | common |
| Weighing error at small scale, where a domestic batch needs quantities smaller than kitchen scales resolve | Stabilisation | common |
| Adding sulphite at bottling on top of an addition made at racking, without accounting for what is already present | Packaging | occasional |
| Using campden tablets of unknown age and strength as if they were a fixed unit | Stabilisation | occasional |
Can it be put right?
Most cider faults cannot be reversed. Where that is the answer it is given plainly — an honest 'this batch is what it is' is more useful than a procedure that will not work.
| Option | Effectiveness | What it involves |
|---|---|---|
| Let the cider rest so that free sulphur dioxide falls naturally | Partial | Free sulphur dioxide does decline over weeks and months as it binds and is consumed. This is the usual answer for a moderately over-sulphited batch, and it costs only time. |
| Aerate the cider to drive sulphur dioxide off | Partial | It works, and it oxidises the cider while doing so. The two effects partly cancel, since the oxidation generates acetaldehyde which then binds the remaining sulphite. A judgement call rather than a clean fix. |
| Blend with an unsulphited or lightly sulphited batch | Partial | Straightforward arithmetic and often the most practical route, if a suitable batch is available. |
| Add hydrogen peroxide to destroy the excess | Unlikely to work | Used in some commercial settings under analytical control. Not a home procedure: the calculation depends on an accurate free sulphur dioxide measurement, and an overdose oxidises the cider outright. CiderHQ publishes no dose. |
| Remove sulphite from a heavily over-sulphited cider so it is fit to label | Not possible | Where a batch is over a legal maximum, there is no domestic route back under it. The cider cannot be sold, and the answer is process discipline next time. |
CiderHQ gives no additive dosage figures. An addition is a food-safety decision that depends on legal limits, on the juice in front of you and on what you are protecting against, and the right figure comes from your supplier’s or regulator’s own guidance rather than from a general reference.
Preventing it
- Measure the pH before deciding on any addition, because pH governs how much of the addition does anything at all.
- Take the rate from the supplier’s guidance for the specific product and from the applicable legal maximum in the country of production, not from a figure remembered from a book.
- Use scales that can actually resolve the quantity involved; where they cannot, make up a stock solution and measure that.
- Keep a written record of every addition to every vessel, so a second addition is made in knowledge of the first.
- Reduce oxygen pick-up, which reduces the acetaldehyde that binds sulphite and therefore reduces the amount needed.
- Where cider will carry a label, check the declaration threshold that applies to it.
Sulphiting is the most consequential decision a small cidermaker makes, and it is made harder by the fact that the correct amount is not a single number. It depends on pH, on what the cider is for, on how long it must keep, and on what has already been added. A recipe that says to add a fixed quantity per gallon is giving an answer to a question that has not been asked properly.
The commonest route to excess is not carelessness but a measurement trap. Free sulphur dioxide binds fast in a cider carrying acetaldehyde, so the reading after an addition looks disappointing, and the natural response is to add more. Understanding the free-and-bound distinction is what stops that loop.
It is worth being clear about what is and is not a hazard. Cider at ordinary sulphite levels is not dangerous to the general population, and the compound has been used in fermented drinks for a very long time. Sulphite sensitivity in a minority is nonetheless real, is the reason for the labelling rule, and is a good enough reason to tell people what is in a drink you have handed them.
There is also a quality cost that has nothing to do with health. Sulphur dioxide bleaches colour and suppresses aroma, so an over-sulphited cider is not only prickly on the nose but noticeably duller in the glass than the same cider would have been.
The compounds involved
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.
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.
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.
Where in the process it arises
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.
Sulphite stabilisation
Managing free sulphur dioxide through maturation and at packaging so that a useful antimicrobial and antioxidant fraction survives into the bottle.
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.
Labelling
Assembling the declarations a container must legally carry, and confirming that the word cider may lawfully be used at all in the market the product is going to.
Faults it is confused with
These present similarly. What separates them is set out on each page.
Acetaldehyde excess
A bruised-apple, green-nut or sherry aroma from acetaldehyde, produced by oxidation, by film yeast, or left behind by a ferment that was interrupted.
Colour loss
A cider left noticeably paler than it should be, usually because fining, filtration or sulphite has removed the phenolic material that gave it colour.
Oxidation
The cumulative effect of oxygen on finished cider: fruit aroma flattens, colour deepens towards amber, and a bruised-apple or sherry-like character replaces the fresh one.
Where this comes up in a guide
The link lands on the step where the fault arises rather than at the top of the pathway, because that is where the decision that causes it is taken.
How cider is made, start to finish
How is cider actually made?
What to measure, and what each number tells you
What should I be measuring, and what do the numbers mean?
When the fermentation is not doing what it should
My fermentation is doing something strange. What is going on?
Structured sensory assessment
How is cider assessed when the answer has to hold up?
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.
- What is oxidation in cider
- 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 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.
- Why does my cider taste like sherry — Acetaldehyde, the compound that sits between alcohol and acetic acid, gives a bruised-apple and sherry-like character. It rises when cider is exposed to air or when a ferment is interrupted.
- Are cider labels regulated
- How is cider bottled
Where to go next
- The fault finder — Describe what you can smell and see, and narrow it down from the signs.
- All faults — Grouped by where they come from and how serious they are.
- Cider science — The chemistry and microbiology these faults come out of.
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.
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.
Regulation (EU) No 1169/2011 on the provision of food information to consumers
European Union · legislation · passage verified 2026-08-24
The instrument behind the "contains sulphites" declaration and the alcoholic-strength labelling rule. Read on 2026-08-24 in the assimilated text maintained on legislation.gov.uk, which is the version in force for Great Britain and keeps the EU numbering. Two provisions matter to cider and both are widely misquoted: the sulphite threshold is 10 mg/L rather than a percentage, and a labelled cider strength carries a tolerance of a full percentage point either way — twice what still grape wine is allowed.
Food labelling and packaging guidance
Food Standards Agency / Department for Business and Trade · regulator · retrieved 2026-08-24