Fault
Light strike
A skunky, cooked-cabbage or drain-like aroma produced when light acting on riboflavin generates sulphur compounds in a bottle.
Also called lightstruck cider, sunstruck.
- Severity
- Quality — the drink is worse for it
- Where it starts
- Packaging, Storage
- Can it be fixed?
- Yes, if caught in time
- When you notice it
- Packaging, Storage
- Signs
- 5 recorded
What it is
Light strike is photochemical damage. Light in the blue and near-ultraviolet range excites riboflavin dissolved in the cider, which then drives reactions on sulphur-containing amino acids and produces volatile thiols with extremely low odour thresholds. The result smells skunky, cabbagey or drain-like. It happens fast — a bottle in direct sun can be affected in an afternoon — and it happens only after packaging, which makes bottle colour and storage the entire control.
What you notice
Grouped by sense, because that is how the fault presents itself rather than how it works.
On the nose
- A skunky or drain-like smell in a bottle that was clean at packaging
- Cooked cabbage or boiled vegetable notes
How the batch behaves
- Bottles from the front of a shelf or a window display being worse than those behind — The most useful diagnostic pattern.
- Clear or green glass affected while brown glass from the same batch is not
- A rapid deterioration over days rather than the slow change of oxidation
The words for it: Lightstruck. Each links to what produces it.
When it appears. In clear or green glass under light, over days to weeks. Brown glass admits far less of the relevant wavelengths and a cider in it is much slower to develop the fault.
The diagnostic question is about the shelf rather than the cellar: a fault present in bottles from the front of a lit display and absent in bottles from the same batch stored dark is light strike and nothing else.
Andrew Lea, Peter Mitchell / Cider and Perry Academy
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 give sulphury notes. Reduction lifts on a hard pour; light strike does not. Ask also where the bottles were kept.
- Mercaptan taint — Origin. Light strike arrives after packaging in bright storage; mercaptans arrive during maturation from an untreated sulphide.
- Colour loss — Both are light-driven. Colour loss without an aroma fault is the milder outcome of the same storage problem.
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.
Riboflavin is present in cider, derived from the fruit and from yeast. It absorbs strongly in the blue and near-ultraviolet, and in its excited state it acts as a photosensitiser, generating reactive species and abstracting hydrogen from other molecules.
The excited riboflavin degrades sulphur-containing amino acids, principally methionine and cysteine, and the fragments produced go on to form volatile thiols including methanethiol and, in beer, the notorious 3-methyl-2-butene-1-thiol. The thresholds are extremely low, so a tiny extent of reaction is enough to be obvious.
The wavelength dependence explains everything practical about the fault. Brown glass absorbs most of the damaging range and gives good protection; green glass gives partial protection; clear glass gives essentially none. A can or a bag-in-box excludes light entirely.
The compounds produced overlap with those of reduction and mercaptan taint, which is why lightstruck cider can be mistaken for a sulphur fault of fermentation origin. The distinguishing evidence is circumstantial rather than sensory: which bottles were where, and in what glass.
How it happens
| Cause | Stage | How often |
|---|---|---|
| Clear glass bottles exposed to daylight or shop lighting | Packaging | common |
| Bottles stored on a windowsill, in a conservatory or in a sunlit room | Storage | common |
| Display under strong artificial light for extended periods | Storage | occasional |
| Green glass used for a cider expected to have a long shelf life | Packaging | occasional |
| Cider transported or left in bright conditions before sale | Storage | 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 |
|---|---|---|
| Move the remaining stock into the dark | Reliable | Stops any further damage to bottles not yet affected. The single most useful immediate action. |
| Change bottle colour for the next batch | Reliable | Brown glass largely solves the problem, and this is the correction that matters. |
| Blend affected cider away | Unlikely to work | The thresholds involved are too low for practical dilution. |
| Reverse light strike in an affected bottle | Not possible | The reactions are not reversible and the thiols are stable enough to remain. |
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
- Bottle in brown glass where the cider will be exposed to light at any point.
- Store and transport bottles in closed cases rather than loose.
- Keep cider out of windows, conservatories and sunlit rooms, at home as well as in trade.
- Consider cans or bag-in-box for products where light exposure cannot be controlled.
- Where clear glass is used for appearance, accept that the cider needs to be kept covered and sold quickly.
Light strike is unusual among cider faults in being entirely a packaging and storage matter. Nothing about the fermentation, the fruit or the cellar affects it; what matters is what colour the glass is and where the bottle has been.
It is also the fastest-acting fault in this file. Oxidation takes months and refermentation takes weeks; a clear bottle left in summer sun can be noticeably lightstruck within hours. That speed is worth knowing because it makes a plausible explanation for a bottle that was fine last week.
The commercial tension is real and worth stating plainly. Clear glass shows a cider off, and a bright, pale cider looks well in it, which is why so much is sold that way. The cost is that the product has no photochemical protection at all, and a bottle standing in a shop window is being damaged while it waits.
Diagnosis relies on pattern rather than on the aroma itself, since the compounds overlap with reductive faults. If the bottles at the front of the shelf are wrong and the ones behind them are not, or if the clear-glass fill is affected and the brown-glass fill from the same tank is not, the answer is light.
The compounds involved
Mercaptans
What hydrogen sulphide becomes if it is left alone: onion, garlic and rubber notes that are far harder to remove than the gas they came from.
Dimethyl sulphide
A sulphur compound that reads as cooked vegetable in quantity and adds an indefinable savoury depth in trace, and which builds slowly during storage rather than during fermentation.
Amino acids
The largest usable nitrogen fraction in apple juice, and the raw material from which yeast builds both its own protein and most of the aroma compounds a cider carries.
Hydrogen sulphide
The rotten-egg gas a nitrogen-starved yeast produces, detectable at concentrations too small to measure easily, and removable only if it is caught before it becomes something worse.
Where in the process it arises
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.
Closure selection
Choosing between cork, crown, screwcap, cage and swing-top, a decision that fixes how much oxygen reaches the cider, whether it can hold pressure, and which faults it is exposed to.
Cellar storage
Holding packaged cider in conditions that let it change slowly and predictably, where stability of temperature matters more than the temperature itself.
Cold chain
Keeping an unpasteurised, unfiltered or back-sweetened cider refrigerated from the packaging hall to the point of sale, because refrigeration is the only thing holding it stable.
Shelf-life management
Establishing how long a cider stays acceptable in its package and setting a durability date that reflects evidence rather than convention.
Faults it is confused with
These present similarly. What separates them is set out on each page.
Mercaptan taint
Onion, garlic, burnt rubber and cooked-cabbage aromas from thiols and disulphides formed when hydrogen sulphide is left in cider long enough to react onwards.
Hydrogen sulphide
A rotten-egg or drain smell from hydrogen sulphide produced by stressed yeast, usually the first visible consequence of a nitrogen-short juice.
Reduction
A closed, stale, slightly sulphurous character in cider held under strongly oxygen-free conditions, sometimes clearing with air and sometimes not.
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.
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.
- How long does cider last — An unopened commercial cider is usually at its finest within a year of packaging, and filtered, pasteurised products carry a stated date. Strong, tannic, bottle-conditioned ciders can improve for several years.
- How do i get rid of the sulphur smell in my cider — Racking with a little splashing usually blows off free hydrogen sulphide while it is still fresh. Once it has reacted into mercaptans the smell becomes rubbery and no longer responds to aeration.
- Does cider need to be refrigerated — Unopened, no — cool and dark is enough for most cider. Unpasteurised, unfiltered cider keeps far better cold, and anything opened should go in the fridge.
- 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.
- Can i use screw top bottles for cider — For still cider, yes. For anything carbonated, a reused screw-top wine or juice bottle is not designed to hold pressure and should not be used.
- 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.
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.
BJCP Beer Style Guidelines — cider and perry categories
Beer Judge Certification Program · classification framework · retrieved 2026-08-24
Opened on 2026-08-24, and the edition matters. CiderHQ registered the 2015 cider guidelines; BJCP has since published a 2025 cider edition, and the old URL now redirects into the current guidelines index. A competition style guide is a dated framework rather than a standing definition, and citing the wrong edition of one is the same class of error as citing a superseded specification. CiderHQ treats BJCP as one competition framework among several and never as the universal cider taxonomy.