Drinking from the Kiddush Cup
Only the one who recited the kiddush is actually required to drink any of the wine or grape juice. Furthermore, only a cheekful of wine or grape juice need be consumed. All others who were present and included in the leader's recitation of kiddush are permitted to begin eating once the leader has drank this amount. There is no obligation for others to drink from the kiddush wine before eating. In fact, even the leader is not truly obligated to drink the wine following kiddush, and he may delegate the actual drinking to someone else present should the need arise.[1]
Nevertheless, there is a widespread custom for everyone who was included in the kiddush to drink from the wine, as well. In fact, doing so is considered to be a mitzva.[2] When drinking from the kiddush cup or even from other wine following the recitation of kiddush, one is not required to recite a blessing. This is because the blessing recited by the leader as part of the kiddush serves to cover any other wine one will drink following the kiddush, as well.[3] However, there are those who have the custom to recite their own blessing over the wine even in this instance.[4] Those who intend to drink from the kiddush wine should be careful not to speak or otherwise interrupt before doing so. If necessary, the minimum amount of kiddush wine that must be drunk may be divided up among a number of people, though it is best if one person alone drinks it.[5]
It is probably better from both a halachic and hygienic perspective to distribute the kiddush wine by pouring it into individual cups before the leader drinks from the kiddush cup itself. The individual cups can then be passed around to all participants.[6] One should wait for the leader to drink the kiddush wine first before doing so oneself. If, however, one had been given wine before kiddush was recited, there would be no obligation to wait for the leader to drink first.[7]
[1] Rosh, Pesachim 10:18; OC 271:14; Rivevot Ephraim 1:194.
[2] OC 271:14; Mishna Berura 272:83; Rivevot Ephraim 6:149.
[3] Mishna Berura 271:63.
[4] Piskei Teshuvot 271:10.
[5] Mishna Berura 271:15.
[6] Mishna Berura 271:83; Sha'ar Hatziun 271:89; Shulchan Shlomo 271 note 27; Rivevot Ephraim 1:194, 6:419, 8:506:4.
[7] OC 271:16.