Some polyphenols give astringent and enhanced mouthfeel characteristics. 7 Others, for example catechin, may function as antioxidants, protecting beer from becoming 'stale' in the presence of oxygen. This can be prevented by removing as much protein as possible through hot and cold precipitation and by using reagents such as silica hydrogels and the proteolytic enzyme papain. Alternatively, they can remove polyphenols altogether by adsorbing them on polyvinylpolypyrolidone. Once fermentation is complete, the main products of S. cerevisiae are ethanol and carbon dioxide.
Ethanol acts directly as a flavour compound, providing beer with warming and vinous notes.
It can also substantially alter the impact of other flavour components, by influencing their partitioning and volatility. In addition, ethanol lowers the surface tension of beer, therefore promoting the ability of beer to foam, though in high concentrations ethanol destabilises foams. 14 Carbon dioxide also has a direct effect on the palate, by triggering the trigeminal pain receptors, albeit in a way that many of us find pleasurable. 17 Adding nitrogen also 'softens' the beer, by suppressing hop aroma and taste. Some polyphenols in beer Countless factors influence the flavour and appearance of beers.