Modelling flavour formation in roasted malt substrates under controlled conditions of time and temperature

Drum roasted products are used to impart colour, flavour and mouthfeel to beers. Here we designed a laboratory-scale roaster (100 g batch size) capable of precise time-temperature control and investigated the impacts of time, temperature and roasting substrate (barley, pale malt or germinated green malt) on formation of 20 key odour active aroma volatiles. Principal Components Analysis (PCA) of flavour volatile data across 37 laboratory roasted and 6 commercial roasted products generated a product flavour space depicting the relationship between roasting conditions and concentrations of these 20 compounds. Response surface models were produced for aroma compound concentrations across the design space of roasting times and temperatures for each substrate. These clearly illustrate the impacts of substrate moisture content and prior history (e.g. whether germinated or germinated and kilned) on flavour formation. In low moisture substrates a steep increase in associated heterocyclic aroma compound production was noted at process temperatures >180 °C.