Biochemical changes occurring during the application of high gravity fermentation technology to the brewing of Zimbabwean traditional opaque beer

Three types of opaque beer were produced, differentiated according to the varieties and ratios of raw materials used in the initial stage of beer preparation. Beer 1 contained sorghum meal and sorghum malt in the ratio 2:1, beer 2 contained sorghum meal and finger millet malt in the ratio 2:1 and beer 3 contained sorghum meal, maize meal and finger millet malt in the ratio 1:2:2. Beers 1, 2 and 3 were prepared under normal and high gravity (HG) fermentation conditions. The time taken to attain the desired sourness and final products varied according to the raw materials used for beer preparation. The pH values of the brews and dissolved solid contents decreased during the preparation process for all the beers. Higher ethanol levels were obtained for the HG beers compared with the normal beers, the maximum ethanol level recorded being 4.74% (v/v) for HG beer 3. Generally, higher free amino nitrogen (FAN) and organic acid levels were obtained in the HG beers as compared with the corresponding normal beers. A sensory evaluation carried out to assess the overall acceptability of the beers revealed HG beers 2 and 3 as having the highest overall acceptability of 82% while HG beer I had the lowest overall acceptability of 27%. (C) 2001 Elsevier Science Ltd. All rights reserved.