phenols
The mechanism of stale flavour development in beer and ways to inhibit staling have long been of interest for the brewer. It is well known, that levels of oxygen in packed beer and shelf storage conditions are important factors in stale flavor development. It is also generally agreed that oxygen pickup and overall reducing potential through out the brewing process, including those Steps prior fermentation, may have a cumulative effect on flavor stability. There are naturally several substances in beer, that have a high reducing potential, to contribute to a better taste stability by reducing the occurrence of stale flavor. They can act by decreasing molecular oxygen levels, scavenging chain-initiating and chainpropagating
free radicals, chelating metals, decomposing peroxides, or changing of volatile aldehyds into non volatile substances. Sulphite, ascorbic acid, superoxiddismutase, phenols and many other compounds will contribute to a good flavor stability.
Phenolic compounds are of considerable significance in brewing. Its most important
aspect is in relation to haze formation. Simple acids are part of the numerous
substances and more highly condensed phenols with protein precipitating and reducing effect. These substances influence colour, foam, stability, flavour and taste. The main part with nearly 80% of these substances comes from the malt, the rest from the hops. The water can also contain such connections but only in very small quantities. Hop extract contains no phenolic compounds; therefore none of these substances can reach into the wort. The use of phenol reduced barley like proanthocyanidin-free barley also leads to a clear reduction of these connections. The effects of these substances on the beer quality are known but there are discrepancies about its meaning in the positive and negative meaning. The low molecular compounds are very strong antioxidants and being able to offer protection against oxidation through it. This has to be judged to be positive. Other groups are directly or indirectly involved in the taste behaviour. This can also be positive and negative. The most important property is their ability to build hydrogen bridges with proteins or with other phenols what can be lead to haze formations.