ROLE OF ALPHA-GLUCOSIDASE IN THE FERMENTABLE SUGAR COMPOSITION OF SORGHUM MALT MASHES

The cause of the high glucose to maltose ratio in sorghum malt worts w as studied. Mashing temperature and pH strongly affected both the amou nt of glucose and the proportion of glucose relative to total fermenta ble sugars. The relative proportion of glucose was higher when mashing was performed. at pH 4.0, close to the pH optimum for sorghum alpha-g lucosidase, than at the natural pH of the mash (pH 5.0-5.5). Mashing a ccording to the EBC procedure using an enzymic malt extract with pre-c ooked malt insoluble solids producing a wort containing maltose and gl ucose in an approximately 4:1 ratio, whereas mashing with a malt extra ct without pre-cooking the malt insoluble solids resulted in a wort wi th approximately equal amounts of maltose and glucose. Both treatments gave the same quantity of total fermentable sugars and amount of wort extract. Sorghum alpha-glucosidase was confirmed to be highly insolub le in water. All or virtually all activity was associated with the ins oluble solids. Hence, it appears that the high amount of glucose forme d when sorghum malt is mashed conventionally is due to alpha-glucosida se activity. Pre-cooking the malt insoluble solids inactivates the alp ha-glucosidase, preventing the hydrolysis of maltose to glucose.