Phenolic materials

In just the same way that the chemistry of the essential oil fraction of hops is enormously complex, so too is that of the phenolic materials contributed to beer by both barley and
hops (Verzele 1986).
We encountered ferulic acid above. Other monomeric phenolic species present in beer include catechin and quercetin. Catechin is rmly accepted as an antioxidant, through its ability both to scavenge oxygen radicals and to inhibit the enzyme lipoxygenase, which promotes the initial breakdown of unsaturated fatty acids to staling carbonyls.

Low molecular-weight contributors to beer aroma

Many people misguidedly believe that most of the avour of beer is derived from its taste. In fact they are detecting the avoursome materials by the nose, there being only four true characters detected on the tongue: bitterness, sweetness, sourness and saltiness
(Bamforth & Hughes 1998).
The confusion about what is detected by tongue and what by nose arises because there is a continuum between the back of the throat and the nasal passages. A beer's smell is the net effect of a complex contribution of many individual molecules. No beer is that simple as to have its aroma determined by one or even a very few substances. The perceived 'nose' is a balance between positive and negative avour notes, each of which may be due to more than a single compound from different chemical classes. Some of these volatile substances come from the malt and hops. A great many, though, are side products of the metabolism of yeast.