Control of selected fermentation indices by statistically designed experiments in industrial scale beer fermentation

Fermentation indices of a bottom-fermented lager brew from high gravity wort (15.5 degrees P) were analysed using the response surface methodology (RSM, Box-Behnken design). Fermentation parameters like pitching rates (6-10 min cells mL(-1)), wort aeration (8-12 mg O-2 mL(-1)), different times (4.5-13.5 h) of filling CCTs (cylindroconical fermentation tanks; 3 850 hL) and fermentation temperatures (8.5-11.5 degrees C) were modulated to assess their impact on the fermentation indices. Within the studied ranges of fermentation parameters the experimental factors had a significant influence (R-2 for the model 73%) on alcohol content, pH (83%), extract drop (86%), FAN consumption (70%), bitterness loss (73%) and sensory analysis (71%). Based on the multiple response optimisation analysis, the values of independent factors that optimised alcohol content at the level of 6.94% (v/v), extract drop at 1.77 degrees P per day with maximization of FAN consumption (ca. 128 mg L-1) and pH drop to the level of 4.69 with minimized bitter substances losses (6.2 BU) were as follows: pitching rate 6 min cells mL(-1); fermentation temperature 11.2 degrees C; aeration level 10.5 mg L-1; and CCTs filling time 13.5 h.