310. Overhearing a Zimmun

45:20 If one who didn’t eat hears others making a zimmun, when he hears the leader say '”Let us bless the One of Whose bounty we have partaken,” he should answer “Baruch u’mevorach Shmo tamid l’olam vo’ed” (“Blessed is He and blessed be His Name, continuously until eternity”). If they are bentching with a minyan, when they say “Let us bless our God…,” he should respond with “Baruch Elokeinu u’mevorach Shmo tamid l’olam vo’ed,” (“Blessed is our God and blessed be His Name, continuously until eternity”). [See Mishnah Brurah 198:6 for the text should this occur at a wedding feast.] If he arrived after the leader said “Let us bless…,” but he hears the other diners replying to the leader, he should simply reply “Amen” after them (and “Amen” again after the leader’s reply – MB 198:4).

45:21 If three ate together, each of his own food, and one of them was eating the bread of a non-Jew, while the other two are stringent not to eat such bread, nevertheless they combine to form a zimmun. The one who ate the non-Jewish bread should lead because he could eat their food while they couldn’t eat his. The same is true if one person ate dairy and the others ate meat; they join together to form a zimmun and the one who ate dairy should lead. This is because he could rinse his mouth out and have their meat but they can’t eat his dairy. If the one who ate dairy doesn't drink wine, or if wine is unavailable and they have to use beer that is chadash (new crop) and he is stringent not to use chadash, then one of the diners who ate meat should lead. This is preferable to having the first-choice person bentch but not to use a cup. (Also, if one of the diners who ate meat is a kohein, that takes precedence over the whole meat-and-cheese issue – Shaar Hatziyon 196:12.) If two diners ate meat and the third ate hard cheese (after which one must wait before eating meat), some authorities maintain that they may not join together to form a zimmun. Others say that they do since they may all eat from a common loaf of bread. One may act leniently in this matter. (The Mishnah Brurah appears to rule stringently in this matter unless the diners actually shared bread – see MB 196:9.)