compound
Acetaldehyde
A green-apple compound produced as an intermediate on the way to ethanol, usually indicating beer served too young.
The full record
Acetaldehyde has its own catalogue entry with the detail this page summarises — mechanism, temperatures and what goes wrong.
Acetaldehyde — A green-apple note indicating beer served before fermentation finished — the classic sign of a rushed product.
Acetaldehyde is a normal step in fermentation — yeast converts it to ethanol given time. Its presence in finished beer typically means the beer was packaged before fermentation completed, or the yeast was removed too early.