ACETALDEHYDE
CHARACTERISTICS: Acetaldehyde has the flavor and
aroma of green apples. It can also taste and smell
acetic/cidery.
CHEMISTRY: Formed as a precursor to alcohol by the
yeast, or as a product of the oxidation of alcohol to acetic
acid.
CAUSES: Acetaldehyde from yeast metabolism as a step
in the production of alcohol from glucose has a crisp
green apple flavor. If produced from the oxidation of
alcohol to acetic acid, whether by oxidation or by
acetobacter, this flavor will be more vinegary and less
pleasant.
PROCESS: As a product of yeast metabolism, it can be
caused by the strain itself or by premature termination of
the yeast's fermentation. The reaction from glucose to
alcohol may be stopped at the acetaldehyde stage by
factors such as oxygen depletion, premature flocculation,
etc. It may also be produced by contamination by acetic
acid bacteria.
REMOVAL: Use a good yeast strain that will attenuate
the wort properly. Oxygenate the wort at yeast-pitching
time. DO NOT splash or oxygenate the wort when
racking or bottling. Long lagering periods will also reduce
acetaldehyde.