Is Baker’s yeast chometz?
A. 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.
This column comes from OU Kosher’s Halacha Yomis dedicated in memory of Rav Chaim Yisroel ben Reb Dov HaLevy Belsky, zt’l, Senior OU Kosher Halachic Consultant (1987-2016). Subscribers can also ask their own questions on Kashrus issues and send them to firstname.lastname@example.org. These questions and their answers may be selected to become one of the Q and A’s on OU Kosher Halacha Yomis.