The Effect of Hydroxycinnamic Acids and Volatile Phenols on Beer Quality

Abstract

To the consumer, beer should be an agreeable beverage of attractive colour, clarity, pleasing flavour and should carry no toxic substances. One of the major constituents of barley is phenolic acids and their direct effect on the quality of beer is still a mystery. The aim of the study therefore was to investigate the relationship between phenolic acids during mashing at different temperatures and the quality of the beer. The mash regime and liquor to malt ratios were optimised and the carbohydrates obtained were analysed at 3.5 L of water per kg of malt and a total mash time of 105 min. Carbohydrate and phenolic acid analyses were performed by HPLC coupled with a UV-vis detector. The three different malts used had a phenolic acid content of 33.25 μg/mL, 25.44 μg/mL and 19.98 μg/mL for malt A, B and C, respectively. The plot of 1/T versus Ln(t) gave a negative slope with activation energy (Ea) = 209 KJ/mol, rate constant (k) = 4.6 × 10−4 mg/L min, which are comparable to similar data reported in the literature. The kinetics studies showed that the optimised mashing temperature of 90°C was adequate to form 4-vinylguaiacol by thermal decarboxylation from the hydroxycinnamic acids. This study has shown that there is no direct correlation between phenolic acids and oxidative flavour stability of beer while the corresponding volatile phenols may affect beer flavour.