Beer flavor and implications of oxidation during brewing.

Van Gheluwe, G.E.A. and Valyi, Z.

Abstract
A review. It is shown that an expert panel can rank both ales and lagers according to their age group up to 4 months in 1 month increments. Copper catalysed oxidase and peroxidase activity during mashing are both important factors contributing to polymerisation of polyphenols. Oxidised polyphenols impart an aged note to beer and fatty acids play an important role in the staling of beer. Promoting haze formation by oxidation during mashing may solve the haze problem but results in a harsh lingering after taste in the beer and the formation of precursors of stale flavour. Fermentations, both ale and lager, should be conducted at temperatures as low as possible. High air levels should be avoided at all costs from the end of fermentation on. The 'spring analogy' is invoked to explain why large variations in oxido - reduced potential between wort and end fermented beer are deleterious. Results of a series of experimental brews show that, by inhibiting oxidase activity during mashing, the resulting beer contains less anthocyanogens and catechins.
Keywords: aging beer brewing fatty acid flavour mashing oxidation polyphenol volatile compound wort