What happens to diacetyl when beer is fermented?

During beer fermentation, the yeast metabolizes itself to produce diacetyl.

Diacetyl is a process term in the brewing industry, and when its content in beer exceeds a certain concentration, beer will develop an unpleasant odor that seriously affects the flavor and taste quality of beer, so it needs to be controlled in the beer production process.

Diacetyl (CH3Cococh3) is an indispensable flavor component in dairy products, but it is not popular in beer, and it is considered to be a rancid flavor, and its taste threshold is about 0·2ppm. If it exceeds 0·2ppm, it is considered that the ripeness of the wine is not enough, or it may be contaminated by miscellaneous bacteria.

Due to the lack of necessary testing equipment in the production of micro-brewed beer, the diacetyl content in beer is above in most cases, which seriously affects the quality of home-brewed beer. In order to solve the problem of high diacetyl content, the production and transformation of diacetyl are as follows. 1. The formation pathway of diacetyl 1. It is formed by non-enzymatic combustion of -acetyl lactic acid by decarboxylation.

The precursor of diacetyl -acetyl lactic acid is an intermediate product of yeast synthesis of valine, -acetyl lactic acid is formed in yeast cells, and then penetrates into the cell through non-enzymatic oxidative decarboxylation to form diacetyl, which is then reduced to 2,3-butanediol under the action of reductase in yeast. 2. Some anaerobic bacteria (mainly syncoccus and lactobacillus, etc.), they can multiply rapidly under post-fermentation anaerobic conditions and produce -acetyl lactic acid and diacetyl at the same time. 3. It is directly formed by the condensation of acetyl-CoA and pyrophosphate (also known as active acetaldehyde) of hydroxyethiamine.

4. After the yeast cells are autolyzed, the -acetaldehyde lactic acid in their body is dissolved in the liquor, and diacetyl will be formed after oxidation.

Diacetyl reduction pathway.

1.Diacetyl is absorbed by yeast and reduced to acetopoly under the action of enzymes in yeast2Acetyl continues to be reduced to 2,3 butylene glycol in yeast, so we can see that although diacetyl is produced by yeast in the process of sugar metabolism during fermentation, yeast can also reduce diacetyl in the later stage of fermentation, and the reduction of diacetyl in the whole beer brewing process can only be reduced by an enzyme in yeast.

Therefore, to reduce the content of diacetyl in beer, it can also be controlled by accelerating diacetyl reduction.