Reducing activity and flavor stability of beer.

Abstract
The reagent 1,1-diphenyl-2-picryl hydrazyl (DPPH) has a free radical form with an intense purple colour, which is stable unless it comes into contact with reducing agents, in which case it is rapidly changed to a colourless reduced form. A number of beer constituents can reduce the DPPH radical, including various polyphenols which are oxidized during the reactions that lead to staling. Experiments are described in which the rate of reduction of the DPPH radical (as determined by the spectrophotometric measurement of the loss of colour) following the addition of degassed fresh beer was found to be negatively correlated with the intensity of staleness of the same beer when tasted after forced aging for 5 days at 37 degrees C. Although the addition of either polyphenols or sulphite to a beer increased its capacity to reduce the DPPH radical, no positive correlation between the sulphite content of beer and its DPPH reducing capacity was found. However, a positive correlation between DPPH reduction and the total polyphenol or anthocyanogen content of beer was observed. The polyphenols involved in this reaction are mainly derived from malt, and their concentration in beer is largely determined by the materials, methods and conditions of wort production.
Keywords : beer flavour off flavour oxidation prospect reduction stability staling