# Which by product of fermentation has been utilized in the production of bread?

$C {O}_{2}$.
Yeasts use sugars in the same way that we do. They convert the sugar to carbon dioxide gas in the fermentation process. If you brew wine or beer at home, you wait until the fermenter stops bubbling $C {O}_{2}$, and the sugars are mostly converted to alcohol (retained) and carbon dioxide (which leaves the fermenter).