James Lucarell, age 9, of Youngstown, Ohio, for his question.

WHAT IS YEAST?

Yeast is used in baking breads and rolls because gas from it helps to cause dough to expand, and it is also used in brewing some beverages. It is actually a microscopic plant that can ferment sugars and starches to make alcohol and carbon dioxide gas.

Yeast plants are single oval cells. They reproduce by a process called budding. New cell buds may be formed every 20 to 30 minutes by yeast growing in sugary or starchy foods that are warm and moist.

Before yeast was commercially grown, each home kept either a pot of potato water or a pan of sourdough as a ferment starter. These home gardens were drawn upon for baking or brewing.