Changes in polyphenols from raw materials to finished beer.

Moll, M., Fonknechten, G., Carnielo, M. and Flayeux, R.

Abstract
The authors describe the extraction, identification and measurement of certain polyphenolic compounds present in beer and brewing raw materials, which are considered to be involved in the formation of non-biological haze. Such compounds include catechin, espicatechin, prodelphinidin and the proanthocyanidins B3, B4, C1 and C2. A reverse phase HPLC method using a C18 column was developed for the purposes of analytical quantitation, detection of the eluted phenols being by means of ultraviolet absorption at 280 nm. The malting process was found to reduce the concentration of catechin in barley whilst the concentration of proanthocyanidin B3 remained essentially unchanged. Experiments with model systems showed that this effect might well be due to differences in oxidation rate. Different barley varieties were shown to markedly influence the initial concentrations of polyphenols solubilised in the mash. However, whilst mash filtration and wort boiling led to the breakdown of the dimeric polyphenols, prodelphinidin and proanthocyanidin B3, and to the formation of epicatechin and additional catechin, every subsequent stage of wort and beer processing resulted in a continued loss and depletion of all the free polyphenols. Consequently their total concentration in the finished beer product was invariably very low (about 10 ppm) irrespective of barley variety. Different varieties of hops and different forms of these bittering agents (pellets, extracts etc.) were however shown to have an effect on the composition of this residual polyphenol fraction. Apart from PVPP, neither absorptive stabilising agents nor enzymes used in the treatment of beer had any effect of the concentration of the free polyphenolic substances. During storage however, their levels in finished beer were seen to diminish still further eventually becoming extremely low (1-2 ppm of proanthocyanidin or catechin). The authors consider that the haze which forms in old beers and contains relatively large amounts of polyphenol cannot be due solely to free proanthocyanidin or catechin in solution at the time of bottling. They support the hypothesis that complex polyphenols formed during mashing are involved in permanent haze formation.
Keywords: S1 analysis barley beer brewing haze hops malt polyphenol raw material