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. 

Explanation:

Acetaldehyde is a colorless, volatile liquid with a pungent and suffocating smell. It is produced as a result of the oxidation of ethyl alcohol to acid or acetic fermentation. Its formula is: CH3CHO formula.

Acetaldehyde occurs naturally in alcoholic beverages. In excess, however, it resembles the smell and taste of an immature green apple.

Fermentation is a process that degrades molecules to transform them into other simpler molecules.

The most frequent causes for which the impurity of acetaldehyde can be generated in fermentation:

It can be caused by the strain of yeast used. To avoid this, a suitable yeast strain should be chosen for the fermentation process. Due to the premature termination of fermentation: In this case it can occur in two different ways: Due to the depletion of must oxygen due to temperature changes and premature flocculation: Acetaldehyde is an intermediate compound in the formation of alcohol, if fermentation stops at the time of the transformation of glucose into alcohol at the stage of acetaldehyde, it produces a fruity flavor and aroma (green apple). For the exposure of alcohol to oxygen: Causing its oxidation and giving immature green apple flavors. Contamination by infection of the bacterium (acetobacter): It is produced as a byproduct of the end of fermentation when part of ethyl alcohol is transformed due to the action of Acetobacter, a genus of aerobic bacteria. For this reason it is convenient that the oxygen level is low at this stage of the fermentation so that the bacteria do not act.

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