Enhancing the levels of 4-vinylguaiacol and 4-vinylphenol in pilot-scale top-fermented wheat beers by response surface methodology

Top-fermented wheat beers are desired by consumers because of their distinctive clove-like and phenolic aroma, in which two characteristic flavour substances, 4-vinylguaiacol (4VG) and 4-vinylphenol (4VP), are of vital importance. In this paper, the levels of 4VG and 4VP were the subject of an intensive and detailed investigation. The influence of wheat malt proportion, mashing-in temperature, boiling time and fermentation temperature on 4VG and 4VP was studied by pilot-scale brewing experiments using a 10 hL mashing vessel and 20 hL fermentation tanks. Response surface methodology (RSM) was used to explore the possibilities for enhancing the concentration of 4VG and 4VP in top-fermented wheat beers. Statistical analysis of the results showed that for the ranges of wheat malt proportion studied, mashing-in temperature, boiling time and fermentation temperature all had a significant influence (p <0.05) on 4VG and 4VP production. Based on the response surface plots, the optimal brewing parameters that maximized 4VG and 4VP levels were as follows: (a) wheat malt proportion 40%; (b) mashing-in temperature 44°C; (c) boiling time 88 min; and (d) fermentation temperature 19.5°C, resulting in significantly increased levels of 4VG and 4VP (2.418 mg/L and 1.402 mg/L, respectively). These brewing and fermentation parameters were concluded to be the optimal conditions to highlight the typical flavour and aroma of top-fermented wheat beers.