Question

Why is yeast used in root beer and bread?

Answer 1

I don't know why it's used in root beer. However, bread uses yeast because the yeast allows the dough to rise and give it the soft and expanded size, shape, and texture it contains.

Answer 2

Yeast in beer makes it bubble. I don't make beer or anything, but I know my microorganisms. It's due to the yeast respiring, which produces CO2 (which bubbles up to the surface).