Summary: The process by which yeast converts sugar into Ethanol, heat and CO2.
The aim of of fermentation is to turn a sugary liquid into an alcoholic one.
Yeast and sugar are needed for alcoholic fermentation to take place. Yeast are microorganisms that are added to the sugary liquid. When they eat sugar they create ethanol and carbon dioxide gas (as a waste product). After fermentation the alcoholic liquid is usually between 8%-10% ABV.
Fermentation also creates extra aromas, in particular, fruity aromas created by the yeast.