Gemara

(The elders of Pumbedisa): One who makes Kidush must taste Malei Lugmav. If he did not, he was not Yotzei.

40b - Question: How can one bless Shehecheyanu [over wine] on Yom Kipur?

Answer: He blesses, and gives the wine to a child to drink.

Pesachim 101a (Rav): People are Yotzei Kidush in the Beis ha'Keneses [even if they did not taste the wine];

(Shmuel): They are Yotzei only if they eat there.

106a: Rav Ashi visited Mechuza. [During the day] they asked him to make 'Kidusha Raba' (the great Kidush. He was unsure if they wanted him to say the entire Kidush of Shabbos night). He said 'Borei Peri ha'Gafen', and saw an elder bend down and drink. (Rav Ash then knew that the Kidush finished.)

107a (Beraisa): It suffices to taste any amount of the wine [of Kidush];

R. Yosi b'Rebbi Yehudah says, [one must taste] Malei Lugmav.

(Rav Huna, and Rav Gidal of Narash's Beraisa): One who makes Kidush is Yotzei only if he drinks Malei Lugmav.

108b (Rav Nachman bar Yitzchak): If one gave from the cup to his household to drink, he was Yotzei. This is only if he drank the majority.

Yoma 80a: One who drinks [on Yom Kipur] Malei Lugmav [is liable].

(Shmuel): 'Malei Lugmav' does not literally mean his full mouth. Rather, it is enough that if he would tilt his head to one side, his cheek would appear full.

Rishonim

Rosh (Pesachim 10:18): 'Malei Lugmav' is like it says in Yoma, that if he would move it to one side, his cheek would appear full. This is less than a Revi'is, like it says there. Also below (108b) we say that one must drink the majority of the cup. [Full] Malei Lugmav is more than a Revi'is, like it says there. Rav Amram and Rav Tzemach Gaon say that if one was Mekadesh and did not taste a Revi'is, he was not Yotzei. I disagree, for we learned that if one who was Mekadesh tasted [Malei Lugmav, he was Yotzei]. If the Mekadesh did not taste, and someone else tasted Malei Lugmav, he was Yotzei, like it says in Eruvin [40b]. One of the others must drink Malei Lugmav. Drinking of two people does not join to Malei Lugmav, for less than this is not considered drinking of Hana'ah. One must benefit from the Kos Shel Berachah!

Rosh (16): Even though everyone need not taste the wine, [we learn from the episode with Rav Ashi that] l'Chatchilah, they should taste.

Ran (Yoma 3a DH veha'Shoseh): The Gemara says that Malei Lugmav in an average person is less than a Revi'is. It is not clear how much less it is.

Tosfos (107a DH Im): Malei Lugmav is for an average person. A giant needs more, like it says in Yoma.

Poskim

Shulchan Aruch (OC 271:13): One must drink from the cup of Kidush Malei Lugmav.

Mishnah Berurah (65): We require a significant Shi'ur that settles a person's mind.

Bi'ur Halachah (DH Tzarich): Malei Lugmav is Me'akev. The Shulchan Aruch uses an expression of l'Chatchilah to teach that l'Chatchilah he need not drink the entire cup.

Kaf ha'Chayim (82): The Beis Yosef says that if he drank less, he was not Yotzei the Mitzvah properly. The Levush says that his Berachah was l'Vatalah. This is wrong. One must make a Berachah Rishonah for any amount!

Note: Presumably, the Levush means that the Berachah "Mekadesh ha'Shabbos" is l'Vatalah!

Shulchan Aruch (ibid.): This is so much that if he would put it in one side of his mouth it looks like his mouth is full.

Question: The Gemara explains that the Shi'ur for Yom Kipur is only k'Malei Lugmav (to fill one cheek). Why didn't it explain this regarding Kidush?

Answer (Drishah 3): It was obvious that a full Malei Lugmav is not required for Kidush, for this is more than a Revi'is in an average person, and the cup requires only a Revi'is.

Mishnah Berurah (67): This is enough, even if the cup holds many Revi'iyos.

Shulchan Aruch (ibid.): This is Rov (the majority of a) Revi'is.

Magen Avraham (29): Malei Lugmav is for an average person. It is more for a big person. In any case he need not drink more than a Revi'is even if this is less than Malei Lugmav (e.g. for a giant).

Kaf ha'Chayim (83): The ideal Mitzvah is to drink at entire Revi'is. This is letter of the law for a big person. Rov Revi'is suffices only for an average person.

Mishnah Berurah (68): Some are very stringent, and proved that our eggs are half the size they were in the days of the Gemara. Therefore, a Revi'is is three eggs of today. One should be concerned for this at night [when Kidush is mid'Oraisa]. In any case the cup should hold at least two eggs. It suffices to drink his Malei Lugmav. One should drink Malei Lugmav in the normal time to drink a Revi'is, without pausing much. Certainly one must not delay Kdei Achilas Pras (the time to eat half a loaf. Some say that this is only two minutes - PF). If he did, b'Di'eved he was not Yotzei. People who make Kidush on whiskey are prone to transgress this.

Bi'ur Halachah (DH v'Hu): In 621:9, the Shulchan Aruch brought the Ran's opinion that Malei Lugmav is less than a Revi'is (not a mere majority). Why did the Shulchan Aruch omit his opinion here? Perhaps there, he teaches an amount for which all agree that he is liable. (The Torah forbids any amount.) The amount one must taste for Kidush is mid'Rabanan. The Shulchan Aruch relied on Tosfos and other Poskim who say that Rov Revi'is is enough for an average person. His words connote that a small person's Malei Lugmav suffices for him, even if he is 13 years old. It need not be Rov Revi'is. Derech ha'Chayim says so. Surely this is so for Yom Kipur, since it settles his mind. This requires investigation. The Gemara says that he must drink the majority of the cup. I.e. if not, he was not Yotzei. Perhaps the Gemara mentioned Malei Lugmav to teach that a big person must drink more than Rov Revi'is. We cannot learn from Yom Kipur, which depends on settling the mind. Perhaps for Kidush, Chachamim obligate drinking majority of the cup of Kidush! Surely according to the Ran, who says that Malei Lugmav of an average person is less than a Revi'is, we can say that Malei Lugmav of a small person is at least Rov Revi'is. However, there is not a solid proof from the Gemara. Perhaps most of the cup even for a small person is Me'akev only for the four cups, but not for a regular Kidush. This requires investigation. When a minor makes Kidush for Chinuch, surely one may be lenient that his Malei Lugmav, which is less than a Revi'is, suffices.

Shulchan Aruch (14): If the Mekadesh did not taste, but one of the others tasted Malei Lugmav (his full mouth), he was Yotzei.

Gra (DH Im): We find that people are Yotzei Kidush in the Beis ha'Keneses even though the Mekadesh does not taste the wine (269:2).

Mishnah Berurah (69): Another's drinking helps only if he was Yotzei the Berachah through the Mekadesh.

Beis Yosef (DH Matzasi): Mordechai Yashan (Sof Yoma) brings from Avi ha'Ezri (Ta'anis 891) 'I received that it suffices to taste a small amount and swirl it around, so his entire mouth tastes it. It says that he must taste Malei Lugmav. Regarding Yom Kipur, it discusses drinking Malei Lugmav.' This is not enough to override the other Poskim.

Kaf ha'Chayim (86): Even though the Halachah does not follow Avi ha'Ezri, if one who hates wine must be Mekadesh, e.g. he is the Ba'al ha'Bayis, he should do like Avi ha'Ezri, and give to someone else to drink Malei Lugmav.

Shulchan Aruch (ibid.): Drinking of two people does not join to Malei Lugmav.

Gra (DH v'Ein): Even if one gave from the cup to his household to drink, he was Yotzei only if he drank the majority (108b). The latter opinion [below] explains 'he was Yotzei only if together, they drank the majority.'

Shulchan Aruch (ibid.): In any case the ideal Mitzvah is for everyone to taste from the wine.

Magen Avraham (30): If one has little wine, just one person drinks a Shi'ur, and he saves the rest for the day Kidush or Havdalah.

Ashrei ha'Ish (2:7:69): Ha'Gaon R. Y.S. Elyashiv Ztz"l says that all should be particular to taste the wine in the morning Kidush, but one is Yotzei even without tasting. The Brisker Rav holds that he was Yotzei only if he tasted [for if not, he was not Yotzei any Berachah].

Shulchan Aruch (ibid.): Some say that since between all of them they tasted Malei Lugmav, they were Yotzei. Their drinking joins to the Shi'ur.

Beis Yosef (DH va'Adoni): The Tur brings from the Rosh that it suffices for others to taste. The Ritva (79b DH Ha) brings from Tosfos that if between all of them they tasted Malei Lugmav, they join.

Mishnah Berurah (72): All agree that l'Chatchilah, the Mekadesh must drink a Shi'ur.

Bi'ur Halachah (DH v'Yesh): We do not protest against those who are lenient, but l'Chatchilah one may not rely on others joining. Derech ha'Chayim says that even if the Mekadesh did not taste at all, he was Yotzei through others.

Mishnah Berurah (73): Many Acharonim agree that b'Di'eved, what everyone drank joins to the Shi'ur, as long as they drink with Kdei Achilas Pras.

Shulchan Aruch (ibid.): The Ge'onim say that if the Mekadesh did not taste, he was not Yotzei. One should be concerned for their opinion.

Gra (DH veha'Ge'onim): The Ge'onim explain that one of the guests [who eats in the Beis ha'Keneses] said Kidush in the Beis ha'Keneses.

Shulchan Aruch (ibid.): This is only regarding Kidush. They agree that for other matters that require a cup, it suffices for another to taste.

Taz (18): This is because there is an Asmachta from the Torah to say Kidush over wine [at night].