In the production of ethanol the process of fermentation is carried out at a low temperature (30⁰-40⁰).

Above 40⁰ the enzymes would permanently lose their structure (denature).

At a temperature lower than 30⁰ the process would be too slow.

 

Fermentation is conducted in the absence of air. In the presence of air (aerobic conditions), enzymes in the yeast produce carbon dioxide and water instead of ethanol.