History

• Egyptians and Babylonians used yeast 5,000 years ago to make sourdough bread and beer although they didn't exactly understand the process. Louis Pasteur was the first person to realize yeast is a single-celled organism and required sugars to ferment. Yeasts are now classified as fungi.

Function

• Yeast is kept dry until needed. In the presence of water and a sugar, yeast feeds and ferments. The by-product of the yeast feeding is carbon dioxide and ethyl alcohol.

Chemistry

• A yeast enzyme called invertase breaks sucrose down into the simple sugars fructose and glucose. Glucose's chemical formula is C6H12O6. The fermentation process breaks apart glucose but conserves its elements resulting in two ethanol molecules (C2H5OH) and two carbon dioxide molecules (CO2)