Improvement of beer flavour with extruded rice as adjunct

Abstract

Extruded rice used as adjunct for beer fermentation was prepared using a single-screw extruder. Extrusion pretreatment facilitated the saccharification and gelatinization of the rice starch as well as the formation of a glassy cellular structure, which was evaluated through scanning electron microscopy analysis. The effects of different parameters, including barrel temperature, water content, nozzle diameter and screw speed, as well as their interactions with rice expansion rate, were evaluated by response surface methodology to determine the optimum extrusion conditions. Extruded rice was acquired using the optimum extrusion parameters (water content, barrel temperature, screw speed and nozzle diameter of 22.4%, 103°C, 8 mm and 191.6 rpm, respectively), and the expansion rate reached 275.1%. The effect of the extruded rice adjunct on beer flavour compounds was investigated by comparing flavour compounds with those of traditional rice-adjunct beer through sensitive static headspace–capillary gas chromatography spectrometry. The contents of esters, a highly important flavour group, in extruded-rice-adjunct beer (ethyl acetate, isoamyl acetate, ethyl hexanoate and ethyl caprylate at 11.6, 2.4, 0.2 and 0.3 mg L−1, respectively) were higher than those of the traditional rice-adjunct beer. The contents of high alcohols were lower in the traditional rice-adjunct beer than those in the extruded-rice-adjunct beer, but both levels satisfied the national standard for beer. Gas chromatography–mass spectrometry was employed to identify the flavour compounds of both beer samples through headspace–solid-phase microextraction. Copyright © 2017 The Institute of Brewing & Distilling