Here's how it works:

* Yeast cells consume sugar (glucose) as their food source.

* Through a series of metabolic reactions, they break down the glucose into simpler molecules, releasing energy.

* The energy produced is used by the yeast cells for growth and reproduction.

* As a byproduct of this process, they release ethanol and CO2.

This process is crucial in various industries:

* Brewing: Fermentation by yeast in beer creates the alcoholic content and CO2 that creates the fizz.

* Winemaking: Fermentation in wine production creates the alcohol content and flavors.

* Baking: Yeast fermentation in bread production produces CO2, creating the air pockets that make the bread rise.

It's important to note that some yeast strains can produce other byproducts, such as small amounts of other alcohols or acids, but ethanol and CO2 are the primary products.