Who Can Join to Form a Zimun?

If two men ate bread and a third joined them for dessert can they join together to form a zimun?

Yes, the third member may join to form a zimun, provided that he ate enough cake, fruit, or any other food, such that he became obligated in a bracha acharona. This means he needs to eat a kezayis (half the volume of an egg) of food, within a time span of k’dei achilas pras (approximately 3 minutes). Even if the men who ate bread already finished their dessert, so long as they potentially could still eat more, (e.g. they did not yet wash their hands for bentching [mayim acharonim]), a third man may eat a kezayis and join them to form a zimun. Moreover, it is considered meritorious for the two who ate bread to offer food to a third person so that they can create a zimun even though they themselves finished eating.

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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.