Bitterness in beer - Compositional changes in various bitter acids upon storage of beer
3 important questions on Bitterness in beer - Compositional changes in various bitter acids upon storage of beer
What happens to the beer flavour during storage?
- The contents of iso-alpha acids and alpha-acids generally decrease even though the beer is stored in dark bottles. Similar to reactions occurring under the influence of light (the bottles do not block the UV-light completely), but at a lower rate.
- Trans/cis ratio decreases
- Alpha-acids concentration decreases more than the iso-alpha-acids
- Concentrations of prenyl flavonoids (isoxanthohumol and xanthohumol) and B-acids increase (no explanation)
By what is the 'light-struck' flavour of beer caused?
- The hop bitter acids, especially the iso-alpha-acids are very sensitive towards UV-light. This light sensitivity determines the type of packaging used. Beer is usually packed metal cans or brown bottles.
- Under UV-light the acids decompose, thereby generating the offending 'skunky' flavour. One of the prenyl chains of the iso-alpha-acid is cleaved off and the highly reactive prenyl radical formed reacts with sulfur-containing compounds (e.g. Derived from cysteine), resulting in the formation of prenyl mercaptan, which gives the off-flavour.
Which is one of the most flavory-active substances in beer?
Prenyl mercaptan.
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