Screening of six local sorghum varieties for their malting and brewing qualities

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Six locally available sorghum varieties were assessed for their malting and brewing qualities. With the exception of Chere, all varieties had suitable 1000 corn weights (>25 g). The differences in corn weights were also significant (p<0.05). Analysis of Germination energy (GE) and Germinative capacity (GC) gave results of >90 % for each variety, signifying their viability. Nitrogen content ranging from1.67 %-2.03 % was obtained for the varieties studied in their unmalted state. Results obtained for malted samples ranged between 1.38 %-1.89 %. With the exception of Dorado (fat 0.96 %), other varieties studied gave high fat contents (i.e. >1.0 %) for the malts. Significant differences were obtained for the malting losses. This ranged between 15.75 % (for Kapaala) and 28.06 %( for Chere). Strong correlation existed between malting loss and Diastatic power (DP) (r=0.803). DP levels for varieties studied indicated that Kapaala (40.07 oWk) was the least modified whiles Chere (60.3 oWk) was the most modified. Differences in DP between varieties studied were significant (p<0.05). The mashing regime and results obtained for Cold water extract (CWE), hot water extract (HWE) and filtration rates showed that all the varieties studied need to be pre-gelatinised before being added to barley malt mash as none gelatinised within malt enzyme temperature range (i.e. 60 OC-70 OC). Results further showed that Kapaala had the highest potential extract (77.94 %) while Sample1 (71.01 %) had the least. In all, the HWE for all the varieties studied ranged between 71.01 % and 77.94 %. Response of mashes to starch check level showed that none of the varieties gelatinises at a temperature suitable for the endogenous amylases. Thus, use of exogenous enzymes or barley malt part mash is required to hydrolyse the sorghum malt starch during the brewing process.
A thesis Submitted as a partial fulfilment of the requirement for the award of Master of Science Degree in Food Science and Technology.