Below are some of the reasons the poskim bring down for the widespread minhag of not drinking from the cup of wine:
1) One Shouldn’t Drink from a Cup and then Give It to A Friend to Drink
The Sdei Chemed (Ma’areches Berachos, siman 31) quotes a letter from the Aderes who writes that it is a clear Gemara in Tamid 27b.
The Gemara in Tamid teaches: “One shouldn’t drink water from a cup and then give it to his talmid to drink, unless he first pours some of the drink over the area that was drunken from.”
The Gemara brings a story with someone who drank from a cup and never poured out from it to clean it, and then gave it to his talmid, and the talmid was an istanis [delicate person] and didn’t want to drink, and he ended up dying from thirst. The Gemara then relates: “At that time, they enacted that one shouldn’t drink water and then give it to his talmid, unless he first washes out the area where he drank from.”
The Aderes says, that although the Gemara is talking about water, there is no reason to differentiate between water and wine. Moreover, the Maseches Derech Eretz Rabbah (Perek 9) says: “One shouldn’t drink from a kois and give it to his friend, as it is a danger”, and normally kois refers to a cup of wine.
This din is brought down l’halachah (Shulchan Aruch, Orach Chaim 170:16 and 22): “Don’t drink from a kois and then give it to a friend, as it is sakonas nefoshos [dangerous]”. “After drinking from a cup of wine, if there is some left and one plans to give it to a friend, one should wipe off the area he drank from, as not doing so is disgusting.”
The Aderes is ma’arich [speaks at length] to prove that there is no difference between a cup of wine being drunk for leisure, or a cup of wine being drunk for a mitzvah.
This approach is slightly difficult, as why can’t the mesader kiddushin drink from the cup of wine and then wipe it clean, like the Shulchan Aruch says to do.
[See the Shemiras Shabbos Kehilchasah (Perek 48, he’orah 69) who asks on the minhag of those who pour kiddush from their cup of wine after drinking from it for others, as seemingly it should be forbidden due to sakonas nefoshos.]
However, the above concern wouldn’t apply in the case of R’ Chaim Brisker and R’ Yosef Chaim Sonnenfeld, as they didn’t drink from cup. However, as we mentioned, there is another reason not to do like this, as doing so is not derech eretz.
2) A Prominent Rav Shouldn’t Drink in Public
The Aderes (there) brings another approach, that since the job of being mesader kiddushin is normally given to a choshuvah rav normally in charge of a large tzibbur [community], it is forbidden for such a rav to drink in public as is clear in Shulchan Aruch (Choshen Mishpat 8:4).
Because of this, the minhag of those who are mesader kiddushin is that they don’t drink from the wine.
3) It Is Not Fitting for a Talmud Chocham to Drink in the Marketplace
R’ Shlomah Zalman Auerbach zt”l in Minchas Shlomah (Vol. 1, siman 18, he’orah 4) brings an additional reason from R’ Zalman Sorotskin zt”l (Shu”t Me’oznayim Lemishpot, siman 9) that since generally speaking chuppah’s are held on the streets, and it is not fitting for a talmud chocham to eat on the street, therefore, the mesader kiddushin doesn’t drink.
However, R’ Shlomah Zalman asks on this, as if it is considered drinking in the marketplace, then the kiddushin should also be considered to be taking place in the marketplace, and Rav would give malkus [lashes] for one who performs kiddushin in the marketplace.
4) A Chosson Is Like a King (חתן דומה למלך ) and It Is Not Fitting to Drink Before the King Does
An additional reason R’ Shlomah Zalman brings down, is that the mesader kiddushin doesn’t drink as a chosson is comparable to a king and it is not fitting for anyone else to drink before him. And for the mesader kiddushin to drink after the chosson is also not respectful, as the mesader kiddushin is a choshuvah rav, and it’s not fitting that he doesn’t drink first, therefore, to save issues he doesn’t drink altogether.
[R’ Shlomah Zalman adds: According to the above, if the chosson and kallah don’t taste from the wine, then the one making the berachah needs to taste from it, and he can’t rely on the fact that other people are going to drink].
The Kovetz Mevakshei Torah (27) brings: Practically, R’ Shlomah Zalman Auerbach and R’ Shach wouldn’t drink from the cup of wine. However, when being mesader kiddushin at a Sephardi wedding R’ Shlomah Zalman would drink from the wine as the Shulchan Aruch (Even HaEzer 34:1) says that the rav who is mesader kiddushin is a shliach [agent] of the chosson.
Machlokes [Dispute] Between R’ Chaim Brisker and the Brisker Rav, If We Say Yotza Moitzi by a Minhag
R’ Berel Soloveitchik zt”l (הגרי''ד), the previous rosh yeshiva of Brisk, would say that he originally thought that it can’t be true that R’ Chaim would make sure to taste some of the wine, and even if he did, it was an old minhag that he did when he was young, however, later on in life he retracted. The reason being, that he never saw his father the Brisker Rav doing it, and if R’ Chaim would have done it, then his son the Brisker Rav would have certainly copied.
However, subsequently he decided that it is actually a machlokes between R’ Chaim and the Brisker Rav, if there is a din of yotza moitzi by hagofen on a cup of a wine only required based on a minhag, and the cup of wine used for birchas erusin is only a minhag.
[R’ Zalman Sorotzkin, in Shu”t MeOznayim Lemishpot (Vol. 1, siman 12) writes in a Teshuvah to the Afikei Yam, that the Brisker Rav told him clearly: שלא ידוע לו הנהגה זו דהגר''ח – “That I don’t know of such a code of conduct by R’ Chaim.”]
However, the sefer Shalmei Sarah (siman 73) brings in the name of R’ Moshe Mordechai Shulzinger zt”l in the name of a chocham eched, that perhaps what the Brisker Rav means is: לא שמיע לי, i.e. I don’t hold of it, but not that he never heard of it.]
The Chosson Who Doesn’t Have Intention to be Yoitza the Berachah
The Afikei Yam points out another issue, which is that even if yotza moitzi does work, however, many times the chosson and kallah don’t have intention to be yoitza with the berachah of the mesader kiddushin, and if the mesader kiddushin doesn’t drink from the wine, then it will end up being a berachah levatolah.
R’ Berel Soloveitchik would say that the Brisker Rav was always upset about the fact that there are unlearned chassanim who don’t have kavonah for this berachah. And because of this, R’ Berel would make up with his gabbah [attendant] beforehand, that he should have intention to be yoitza with the berachah, and he would give him to drink. (This is the Brisker Rav in accordance with his own opinion, that he wasn’t worried about the question of the Pnei Yehoshua, that if one isn’t drinking, he can’t make a berachah for someone else.)
(Based on a Teshuvah written by R’ Avraham Sanger, cited in Madanay Yom Tov, Vol. 9, siman 32)
