Question:

Why is it permitted to drink wine on Passover when it is fermented with yeast? Isn't yeast forbidden on Passover?

Answer:

Of the hundreds of species of yeast, the Passover prohibition only applies to yeast which is a product of one of the following five grains: wheat, barley, oat, spelt, or rye. Yeast which is the product of grapes, or its sugars, is not considered chametz (leavened food).

Click here for more about chametz.

Have a Kosher and happy Passover!

Rabbi Dovid Zaklikowski
Chabad.org