Yeast is a fungus. It is an essential ingredient in bread making. If you mix it with sugar and water it produces carbon dioxide. It gives the baked products soft and spongy texture. Most yeast is used in baking but some of them can be used in alcoholic fermentation. The fresh yeast is only available at bakers. Dried active yeast is used for hand baking. Easy bake yeast can be used in bread machines. It can be kept in a cool dry place.