I’ve noticed an off flavor in my beer, trying to determine what it might be and someone I know mentioned Acetaldehyde, what is that?
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: Yeast metabolism (fresh-cut apples) uses acetaldehyde as a step in the production of alcohol from glucose. This is a fresh, fruity flavor. The second cause is the oxidation of alcohol to acetic acid, whether by oxidation or by acetobacter (gram-negative). 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, such as oxygen depletion, premature flocculation, etc. such that the reaction from glucose to alcohol is stopped at the acetaldehyde stage.
The other causes are oxidation and contamination by acetic acid bacteria. This will occur during splashing when racking quiet beer (non-kraeusened) and bottling.
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.
EXAMPLES: Budweiser deliberately manipulates their yeast and process to give 6-8 ppm acetaldehyde in the beer.