How does acetaldehyde impurity arise in the fermentation?

Acetaldehyde is a compound that has a chemical formula which can be written as CH₃CHO. This can be oftentimes abbreviated as MeCHO, signifying the presence of methyl (Me). This is a colorless and flammable liquid.

This finds its way to the fermented products because in the process of fermentation, this is naturally produced in one of the intermediate step that would convert the sugars to carbon dioxide and ethanol. Depending on the strain of the bacteria that acts on the substrate then, this may be formed in large quantities. Acetic acid bacteria (AAB) has a high tendency of producing large quantity or favor the production of acetaldehyde.