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Phenolic acids in beer are important because they can be decarboxyiated to phenols, which usually impart off-flavours. An improved high performance liquid chromatographic system was used to monitor phenolic acids and phenols during the brewing process. Ferulic acid was the most significant phenolic acid found in beers prepared from malted barley. Extraction of ferulic acid from malt involved an enzymatic release mechanism with an optimum temperature about 45°C. Mashing-in at 65°C significantly decreased the release of free ferulic acid into the wort. Wort boiling produced 4-vinyl guaiacol by thermal decarboxylation, in amounts (0.3 mg/L) close to its taste threshold, from worts that contained high contents of free ferulic acid (> 6 mg/L). The capacity of yeasts to decarboxylate phenolic acids (Pof* phenotype) was strong in wild strains of Saccharomycoa and absent in all lager brewing yeast and most ale brewing yeasts. Some top-fermenting strains, especially those used in wheat beer production, possessed a weak decarboxylating activity (i.e. Pof1). During storage of beers there were appreciable temperature-dependent losses of 4-vinyl guaiacol. These results indicated that the production of 4-vinyl guaiacol is amenable to close technological control.

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A semipreparative chromatographic method for the isolation of small amounts (10−20 μg) of dimeric and trimeric proanthocyanidins from barley is described. Concentrated extracts of barley were injected onto a high-performance gel filtration column (Superdex 75 HR), and were eluted with methanol. This procedure resolved the dimeric proanthocyanidins (prodelphinidin B3 and procyanidin B3), as well as the trimeric procyanidin C2 and three other trimeric prodelphinidins. The separated flavanoid peaks were collected and their contents were estimated by UV spectrophotometry, reaction with p-dimethylaminocinnamadehyde, and reversed phase HPLC with electrochemical detection. This method produced proanthocyanidins in sufficient amounts to calibrate a system for direct injection chromatographic analysis of beers and barley extracts. The method described may be optimized for the isolation of dimeric proanthocyanidins only, in which case the preparation can take as little as 3 h; alternatively, by extending the chromatographic separation to 9 h, the four major trimeric proanthocyanidins of barley can be recovered also in a chromatographically pure state. Keywords: Analysis; barley; beer; calibration standard; high-performance liquid chromatography; proanthocyanidin

A method was developed to determine the flavanols prodelphinidin B3, procyanidin B3, (+)-catechin, and (-)-epicatechin by high-performance liquid chromatography, using dual-channel electrochemical detection. This method was especially suited to the direct analysis of beer samples and to analysis of acetone extracts of barley samples, and was capable of determining proanthocyanidins and catechins at levels of 0.1-5.0 mg l-1. The use of dual-channel electrochemical detection also enabled unambiguous peak identification by measurement of collection efficiencies. This method offered improved sensitivity and selectivity compared with ultraviolet detection, and sample preparation procedures were greatly simplified. The method was applied to the comparison of stabilized and unstabilized lagers, and to the analysis of different barley varieties grown in Ireland.