In a previous edition of Daily Halacha, we saw that if two people ate bread together, and a third person joined them after they had completed their meal, the three of them can make a Zimun if several conditions are met. Specifically, the first two must not have washed Mayim Aharonim or said, “Hab Lan Nibrich”; they must be willing to delay Birkat Hamazon until the third person finishes eating; and they must have enough room for some more food if it were served.
What must the third person eat to allow for a Zimun? Must he eat bread, or does it suffice for him to eat other foods?
In general, there is a debate among the Rishonim (Medieval Halachic scholars) as to which foods the third person must have eaten to require a Zimun if the other two ate bread. Some Rishonim maintain that the third person must have eaten either bread or Mezonot food, which resembles bread. (If a person eats a very large quantity of Mezonot food, he is required to recite Birkat Hamazon, and it thus resembles bread.) Others, however, maintain that he may eat even other foods. As for the final Halacha, Rabbi Moshe Halevi (Israel, 1961-2001) writes in Birkat Hashem that it is preferable for all three people to eat bread, but if the third person ate other foods, or even drank something other than water, they have an obligation of Zimun. However, he adds, this applies only if the three ate together and they must now determine whether they must recite a Zimun. But in the case described earlier, where two people ate together and were joined by a third person after they finished eating, they should not allow the third person to join them unless he will be eating bread or Mezonot. If he eats other foods, they are putting themselves in a situation of Safek (Halachic uncertainty), and they should therefore avoid this situation by insisting that the third person join them only if he will eat bread or Mezonot food. This is different from a case where three people happened to eat together and must now determine whether to recite a Zimun, as there they did not from the outset knowingly create a situation of Halachic doubt. In the case of a third person who joins two people, he should be allowed to join only if he will eat foods that will require them to recite a Zimun according to all opinions. Rabbi Moshe Halevi notes that this is the view of the Hida (Rav Haim Yosef David Azulai, 1724-1806), in his Haim Sha’al, and of the Kaf Ha’haim (197:21).
Hacham Ovadia Yosef, however, disagrees. In his work Yehaveh Da’at (4:13, p. 66), he writes that this situation is not actually one of Safek, and therefore the third person may join the first two even if he will not be eating bread or Mezonot food. As long as the aforementioned conditions are met, the third person may join the first two and eat something, and they then recite a Zimun before Birkat Hamazon.
Summary: If three people ate together, two of whom ate bread while the third ate other foods, they must recite a Zimun, though it is preferable for the third to also eat bread or Mezonot food so they may recite a Zimun according to all views. If two people ate together and before they washed Mayim Aharonim or expressed their intent to recite Birkat Hamazon they were joined by a third, the third may join them and make a Zimun even if he eats foods other than bread or Mezonot food.