WAEC Chemistry 2015 Theory — Question 29

Model answer

The starchy material is first ground and hot water is added to liberate the starch; the temperature is maintained around 57.5°C. Malt (partially germinated barley), which contains the enzyme diastase, is added, converting the starch to maltose. The temperature is then lowered to around 20°C and yeast is added; the enzyme maltase in the yeast converts maltose to glucose (via hydrolysis), and the enzyme zymase converts the glucose to ethanol, carbon (IV) oxide, and energy.