Yeast

Yeast, on the other hand, is a live, single-celled fungus.

There are about 160 species of yeast, and many of them live all around us.

However, most people are familiar with yeast in its mass-produced form:
the beige granules that come in little paper packets.

This organism lies dormant until it comes into contact with warm water.

Once reactivated, yeast begins feeding on the sugars in flour, and releases the carbon dioxide that makes bread rise (although at a much slower rate than baking powder or soda).

Yeast also adds many of the distinctive flavors and aromas we associate with bread.