Flavour control in small-scale beer fermentations

Fermentation productivity can be improved by the use of high temperatures, high yeast pitching rates and high wort specific gravities. However these approaches can lead to altered beer flavour and detrimental effects on yeast viability and vitality. Our investigations have sought to help us understand how process variables affect beer flavour profiles with the aim of developing intensified processes which produce beers with normal flavour characteristics. In order to assess the interactive effects of process variables on beer flavour production, statistically designed fermentation trials were performed using a range of process conditions. Empirical correlations were derived for predicting the average yields of some flavour volatiles and for predicting fermentation time. Higher temperatures and higher yeast pitching rates yielded faster fermentations. Ester yield was reduced under conditions of high wort aeration, lower temperature, lower wort gravity and higher pitching rates. The yield of higher alcohol was generally reduced under conditions of lower temperature, lower initial aeration levels and higher gravity. The effect of pitching rate on the yield of higher alcohol was strongly dependent on the wort gravity used. Comparison of the predicted flavour volatile yield and process time 'maps' indicate operating zones where process intensification occurs, without changes to flavour volatile concentration.