The Ge’onim (Babylonian scholars in the post-Talmudic era) were of the opinion that when a person recites Kiddush on Shabbat, he does not fulfill the obligation unless he personally drinks the minimum required Shiur (quantity) of wine from the Kiddush cup. Even if somebody else at the table heard the Kiddush and then drank the Shiur, nobody fulfills the obligation if the Mekadesh (person who recited Kiddush) did not drink the minimum required amount.
The Shulhan Aruch (Orah Haim 271:14), however, does not follow this opinion. He rules that although it is certainly preferable for the Mekadesh to drink the required Shiur, if this is not possible, then he may give the cup to somebody else to drink. Assuming that this individual had heard the Kiddush, and the Mekadesh had intended for his Kiddush recitation to fulfill the obligation for this person, that person may drink the Shiur of wine, and then everyone who heard Kiddush fulfills their obligation.
How can a group fulfill the obligation of Kiddush if no one is able to drink the minimum required amount of wine?
The Shulhan Aruch cites an opinion that a group can fulfill the obligation even if the Shiur is drunk collectively, meaning, if several people each drink a small amount, such that altogether they drink the minimum required amount. According to the accepted Halacha, however, this opinion may be relied upon only Be’di’abad (after the fact), meaning, if the Mekadesh recited Kiddush and no single individual drank a complete Shiur. In such a case, they do not need to repeat Kiddush, and may instead rely on the view that the collective consumption of the Shiur suffices to fulfill the Misva. However, they may not plan from the outset to have each person drink a small sip, without any individual drinking a complete Shiur.
What, then, should a group of people do if they know from the outset that no member of the group is able to drink a complete Shiur of wine?
Rav Moshe Halevi (Israel, 1961-2001), in his work Menuhat Ahaba, writes that in such a case, the group should recite Kiddush on bread, and not on wine. This option is Halachically preferable to having each person drink only a small sip of wine.
Summary: When a person recites Kiddush on Shabbat for a group of people, he should preferably drink the Shiur (minimum required amount) of wine from the Kiddush cup. If he is unable to drink the Shiur, then he may have somebody else at the table drink the Shiur. If nobody at the table is able to drink the Shiur of wine, then they should recite Kiddush over bread, and not over wine. However, if they mistakenly recited Kiddush over wine, and each person drank a small sip of wine, such that they collectively drank the minimum required amount, they have fulfilled their obligation. Preferably, however, in such a case they should recite Kiddush over bread.
