Is Baker’s Yeast Chametz?

The se’or prohibited by the Torah does not refer to baker’s yeast. Se’or is sourdough, which is made by allowing raw dough to become moldy and capable of leavening future dough. Baker’s yeast, however, is a microorganism propagated on various media, typically, in its final production stage, on molasses. It can be sold before Pesach even by people who are careful to avoid selling chametz gamor. Baker’s yeast should not, however, be consumed on Pesach. Even if a manufacturer claims that the medium for producing yeast is molasses, it should not be used. The production process for yeast involves multiple stages, and it is possible that the manufacturer is referring only to the final production stage.

The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt”l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.