Glossary
Lightstrike
The skunky aroma produced when light breaks down hop-derived iso-alpha-acids into a thiol closely related to a component of skunk spray.
Also called skunked, skunky, lightstruck, sunstruck.
The full record
Lightstrike has its own catalogue entry with the detail this page summarises — causes, thresholds, related styles and evidence.
Lightstrike — Light breaks down hop compounds into a thiol chemically close to skunk spray — the fastest fault in beer, and entirely preventable.
It happens in minutes of direct sunlight and over days under fluorescent light, and it is entirely independent of the beer’s age. A brand-new bottle left in a shop window will skunk; a five-year-old can never will.
Brown glass absorbs most of the responsible wavelengths, green and clear glass do not, and aluminium blocks light entirely. Some breweries use chemically modified hop extracts whose isomerised acids cannot form the compound, which is how a few well-known lagers ship in clear glass without skunking.
Commonly misunderstood
Skunkiness is routinely described as beer having "gone off". It is a photochemical reaction, not spoilage, and says nothing about the beer’s age.
Related
- Lightstrike — The fault record.
- Green glass bottle — The packaging most associated with it.
More vocabulary
Acetaldehyde · Autolysis · Bottle bomb · Diacetyl · DMS · Gushing · Oxidation · Staling
See every term on the glossary index.
Last reviewed 2026-08-16.