| Summary: | Roasted malts are used in the brewing industry to impart colour and flavour to beers. The diversity of colours and flavours roasted products can provide are dependent upon a variety of factors: roasting time and temperature, initial moisture content, roasting substrate type (i.e. green malt, pale malt, or unmalted barley), and roasting sequence (i.e. stewing, kilning, and/or roasting). The aim of this research was to improve understanding of thermal flavour generation in roasted malt and barley, and thereby improve understanding of roasting process control. In this research, instrumental analysis was employed to positively identify and quantify thermally generated volatile compounds in roasted products, while sensory analysis evaluated the odour activity of identified volatiles, and quantitatively described aroma qualities of roasted products.
Gas Chromatography-Olfactometry (GC-O) identified 45 odour active compounds across a range of six commercially available roasted malts. Of these, formation of 20 key compounds were monitored as a function of roasting time and temperature across the three roasting substrate types, using a custom-built laboratory-scale roaster for precise time/temperature control. 3D response surface models were produced showing compound concentrations as a function of roasting time and temperature in each roasted substrate. The roasted product ‘flavour space’ (depicted via principal component analysis (PCA)) visualised formation of 20 compounds over the course of roasting conditions for each roasted substrate, in addition to the six previously examined commercially roasted products. The identification of volatile sulphur compounds (VSCs) by GC-PFPD (Pulsed Flame Photometric Detection) in roasted products presented novel detail of VSCs in roasted products, showing the highest numbers of VSCs in products roasted between 200 °C and 230 °C, however, prolonged roasting times reduced concentrations. Quantitative Descriptive Analysis (QDA) of the aroma of selected roasted products identified roasting temperature as the major significant factor in the aroma characteristics of roasted products. This research provides comprehensive understanding of thermal flavour generation in roasted malts and barley by the interdisciplinary approach of combining instrumental and sensorial analysis. Awareness of volatile formation as a function of process conditions has potential to improve process control and product quality for commercial roasting.
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