Explanation

Yeast is a facultative aerobe. When yeast is grown in a well aerated (Aerobic) nutrient medium, the sugar is completely oxidized in normal respiration. $C_{6}H_{12}O_{6} + 6O_{2} \rightarrow 6CO_{2} + 6H_{2}O + Energy$ But in anaerobic condition, sugar is converted into carbon dioxide and ethyl alcohol $(C_{2}H_{5}OH)$ within the cytoplasm. $\ _{\ \ \ Glucose\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Ethyl\ alcohol\ \ }^{C_{6}H_{12}O_{6}\ + \ Yeast \rightarrow 2C_{2}H_{5}OH\ + \ CO_{2}\ + \ Energy}$