Biochemistry in Beer Brewing

Alcoholic fermentation is concerned primarily with the production of ethanol by the action of the fermenting yeasts. The biochemical process involved in fermentation is glycolysis mediated through the Embden-Meyerhoff- Parnas pathway outlined in the figure below.

Flavor Compounds

1. Alcohols

• Produced from wort carbohydrates via oxo-acids of from transamination and deamination of amino acids in wort.
• Include both the aromatic alcohol 2-phenylethanol as well as such aliphatic alcohols as butanol, propanol, and hexanol.

2. Esters

• Most important group of beer volatiles providing strong fruity flavors.
• Formed via lipid metabolism by yeast in which acetyl-CoA reacts enzymatically with different alcohols, as shown here for ethyl acetate:

• amount of esters formed during fermentation depends on the yeast strain, fermentation temperature, and aeration of wort.

3. Carbonyl Compounds

• Attribute to the "buttery, honey-or toffee-like, or butterscotch" flavor in beer.
• Most important formed during fermentation are diketones such as diacetyl and pentane-2,3-dione.
• Formed from oxidative decarboxylation of oxaloacetate and acetohydroxybutyrate.

Beer Brewing

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