A new thermotolerant UV- mutant strain Saccharomyces cerevisiae UV4 based on its invertase activity was selected and found to possess higher temperature (40ºC) tolerance, higher growth rate and fermenting ability than the parent strain Saccharomyces cerevisiae 101. At 40°C, the final ethanol concentration was increased by more than 45% by the mutant on fermentation of sweet sorghum medium supplemented with total yeast nutrients. A 2.0 gl^-1 addition of nitrogen sources namely urea, ammonium sulphate, yeast extract and skim milk solids has increased the ethanol yield by 29%, 27%, 37% and 33%, respectively. Batch yeast cell recycle has contributed to the formation of 17% more ethanol in the presence of skim milk supplement than the control, as it saved 5-6% of sugars required in the build up of the initial yeast inoculum.