Acetylaldehyde

This is a common flavour chemical in spirits. It is also the chemical that ethanol is converted to, in the body, and one that causes the majority of a hangover.

Acetaldehyde as Key Compound for the Authenticity of Sherry Wines: A Study Covering 5 Decades
https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12159