that the temperature of 30oC is the optimum temperature for fermentation of whey by Kluyveromyces marxianus. It occurs because the increase in temperature may be due to the reduction in the activity or inactivation of the enzyme β-galactosidase [13]. While the ethanol yield at a temperature of 300C (0.21 g ethanol/g substrate) is greater than the temperature of 350C (0.19 g ethanol/g substrate).