Gemara

Version #1 (Rashi): If one ate (a quarter loaf of) Tamei food, drank (a Revi'is of) Tamei liquids, if the delay was bi'Chdei Achilas Pras, (he became Tamei);

If one drank a Revi'is of wine within this time and entered the Mikdash, he is liable.

Version #2 (in Shitah Mekubetzes 12): If one ate (a quarter loaf of) Tamei food, drank (a Revi'is of) Tamei liquids, or drank a Revi'is of wine and entered the Mikdash:

If the delay was bi'Chdei Achilas Pras, he is liable (mid'Oraisa for wine, and mid'Rabanan if he consumed Tamei food or drink).

R. Eliezer says, if he paused while drinking the wine, or added any water to it, he is exempt.

Question: Is R. Meir more lenient than Chachamim, or more stringent?

Does he mean that he can delay all day, like one who eats crumbs, even if the total time (delay) exceeds Kedei Achilas Pras? This is a stringency;

Chachamim reply that he is not liable unless he ate bi'Chdei Achilas Pras.

Or does he mean that he must eat without pausing, like one who eats crumbs, but if he paused he is exempt, even though he ate a Shi'ur within Kedei Achilas Pras. This is a leniency;

Chachamim reply that since he delayed at most Kedei Achilas Pras from beginning to end, he is liable.

13a (Beraisa): All (Tamei) drinks join to the Shi'ur of a Revi'is to be Metamei one who drinks them bi'Chdei Achilas Pras (within the time needed to eat half a standard loaf, i.e. the volume of three or four eggs). If one drank intermittently, he becomes Tamei only if he finished bi'Chdei Achilas Pras of when he began.

Chachamim permitted a woman who touched one who is Tamei Mes (she is a Rishon l'Tum'ah) to nurse a baby, and the baby remains Tahor.

Question: Why is the baby Tahor? He ingested Tamei milk. This should be Metamei him!

Answer (Rava): The baby is Tahor because of a Sfek Sefeika (two doubts). Perhaps he did not ingest a Shi'ur of milk. Even if he did, perhaps this was not bi'Chdei Achilas Pras!

(Mishnah): If one drank Tamei liquids, or drank a Revi'is of wine, and entered the Mikdash, if the delay was...

Question: One is liable for entering (while Tamei or drunk) even without any delay!

Answer (Rava): It means that if he drank bi'Chdei Achilas Pras, and then entered the Mikdash, he is liable.

Rishonim

Rambam (Hilchos Shevisas Asor 2:4): If one drank a little, and drank again, they join to a Shi'ur (to be liable) only if from the beginning of the first drinking to the end of the last was (at most) the time to drink a Revi'is.

Magid Mishneh: This is from the Tosefta (Yoma 4:4). The same applies to all Isurim, like the Rambam says in Hilchos Ma'achalos Asuros. Some learn from Kerisus that the Shi'ur is Kdei Achilas Pras. Chachamim strengthened their enactment to be Metamei one who drinks Tamei liquids (therefore, they used the larger Shi'ur of time). In Kerisus, we find that Shmuel is more stringent about the Shi'ur of (time to eat) Tamei food and drink than regarding other Isurim. Therefore, we distinguish Tum'ah from other Isurim, and we need not reject the Tosefta in Terumos. The Ritz Gei'us wrote so in his Halachos.

Rambam (Hilchos Ma'achalos Asuros 14:9): If one drank bit by bit a Revi'is of blood or Stam wine of Nochrim, or melted Chelev or Chametz during Pesach and drank it slowly, if he delayed more than the time to drink a Revi'is, they do not join.

Rambam (Hilchos She'ar Avos ha'Tum'ah 8:11): All Tamei drinks join to the Shi'ur of a Revi'is to be Metamei one who drinks them bi'Chdei Achilas Pras.

Rambam (12): If a Rishon l'Tum'ah nursed a baby, the baby remains Tahor. Chachamim did not decree Tum'ah on him, for even if he nursed a Revi'is, for perhaps he paused from the beginning to the end more than Kdei Achilas Pras, since he does not nurse at once.

Rambam (Hilchos Terumos 10:3): If one drank and drank again, they join to a k'Zayis only if from the beginning of the first drinking to the end of the last was (at most) the time to drink a Revi'is.

Rebuttal (Ra'avad): Indeed, the Tosefta says so, but in Kerisus we say that the Shi'ur even for drinking is Kdei Achilas Pras. Also the Tosefta in Pesachim says so.

Radvaz: Why did the Rambam reject the Tosefta in Pesachim? Since the Shi'ur for eating and drinking (is the same), it is more reasonable to equate the Shi'urim of time for eating and drinking! Regarding Terumah, the Rambam favored the Tosefta in Terumos, which is in the Masechta teaching about Terumah, over the Tosefta in Pesachim, which discusses Chametz. The Rambam rules similarly regarding Yom Kipur, and in Hilchos Ma'achalos Asuros regarding wine of Nochrim, Chametz, Chelev and blood. He equates Chametz to other Isurim. Granted, when the Shi'ur for drinking is a k'Zayis, even if one pauses, he can drink it within the time to drink a Revi'is. However, when the Shi'ur is a Revi'is, if he pauses, how could he drink a Revi'is in the time to drink a Revi'is! With difficulty, we can say that he drank (part) quickly, like gluttons do, paused a little, and drank again quickly, and finished a Revi'is in the time that normal people drink a Revi'is. In Hilchos She'ar Avos ha'Tum'ah, the Rambam says that liquids join within Kdei Achilas Pras! They answered that Chachamim strengthened their enactment about drinking Tamei liquids. (The Radvaz cites the Magid Mishneh above verbatim.). The Ritz Gei'us says that since Chachamim were more stringent about drinking Terumah wine (the Shi'ur is a k'Zayis, and not a Revi'is), they were lenient about the time, and it joins only in the time to drink a Revi'is (and not Kdei Achilas Pras). I answer that other Isurim are forbidden because the throat enjoyed Isur. If one delayed longer than the time to drink a Revi'is, the throat did not enjoy a Revi'is at once. Disqualifying the body from Terumah does not depend on Hana'ah, rather, on liquid joining in the body. If he delayed at most Kdei Achilas Pras, it joins and disqualifies the body. In a longer time, the liquid disperses amidst the body and it is Batel, and does not disqualify the body.

Kesef Mishneh: Our text of the Tosefta in Pesachim says 'the time to drink a Revi'is.' The Ri Korkus says that Isurim are forbidden because the throat enjoyed Isur. The Hana'ah joins over the time to drink a Revi'is. The Hana'ah from food lasts longer, so it joins up to Kdei Achilas Pras. Tum'ah of the body does not depend on Hana'ah. Even if someone stuck Tamei food in Ploni's throat (and he swallowed it unwillingly), he becomes Tamei. Therefore, we do not distinguish between eating and drinking.

Poskim

Shulchan Aruch (OC 210:1): One who drinks less than a Revi'is of wine or other drinks blesses beforehand, but not afterwards.

Mishnah Berurah (1): If one paused in the middle of drinking, some say that the two times do not join. Some say that they join up to Kdei Achilas Pras. It is normal to drink hot tea or coffee, and it is hard to drink it like other drinks, without stopping. Opinions differ about whether one should say a Berachah Acharonah. The custom is not to bless. Meticulous people let a Revi'is cool off, so they can drink it without pausing. It is good to do so, to fulfill all opinions, especially since the Gra holds that up to Kdei Achilas Pras joins.

Yafeh l'Lev (9, cited in Yabi'a Omer 5 OC 18): My father (Kaf ha'Chayim (Palagi) 22:25) advises to drink a Revi'is of water before the coffee, and to say the Berachah Acharonah with intent for both of them. He discusses one who is thirsty for the water. If not, one does not bless before or after water. Also, one should bless first on what he prefers. I say that in any case it is better to bless on the coffee beforehand.

Kaf ha'Chayim (Sofer) (204:40): If one drank a Revi'is of coffee, many say not to bless, and many say to bless. Beis Yehudah (OC 7) concludes like those who say not to bless, and this is proper because Safek Berachos Lehakel (when in doubt, we do not bless). The Birkei Yosef (5) says that this is the custom is Turkey, Mitzrayim and Eretz Yisrael. Chayei Adam, Kitzur Shulchan Aruch and Ben Ish Chai also say so. Since there are two opinions, it is best to exempt it through something else. If one cannot, he should think the Berachah in his heart.

Ginas Veradim (OC 1:17): People drink a Revi'is of coffee and do not bless afterwards. Perhaps one must bless a Berachah Acharonah even on less than a Revi'is! Tosfos was unsure; the Tur (OC 205) brought this. Even if the Shi'ur is a Revi'is, perhaps it joins over Kdei Achilas Pras, like the Ra'avad holds! The Magid Mishneh (see the Radvaz above) struggled to explain how the Shi'ur for drinking a Revi'is can be the time to drink a Revi'is. Even though the Shi'ur for eating is much less (a k'Zayis), if one melted a food and made it a liquid, we are lenient to obligate only for a Revi'is. (According to the Rambam) we are further lenient not to join over Kdei Achilas Pras, rather, only in the time to drink a Revi'is. Since now it is a liquid, this is the normal way to benefit from it, even though initially it was a solid. Regarding Yom Kipur, if one ate salt with meat, it joins to the Shi'ur, for he benefited in the normal way. Similarly, if one melted Chelev and drank it slowly while it was warm, even if he delayed a long time, he is liable even according to the Rambam. The Seifa of the Rambam connotes like this. He exempts one who swallowed hot Chelev and burned his throat. It seems that he is exempt only because he burned his throat. If not he would be liable, even though he drank slowly, for this is the normal way of benefit. I bring a proof for this from Kerisus.

Note: The rest of the Teshuvah is missing from Ginas Veradim. The following is from Teshuvas Zera Avraham Yitzchaki, who cites it.

Ginas Veradim: The Rambam concludes 'the baby does not nurse at once.' Why did he need to say this? He teaches that if a baby would nurse normally, slowly without stopping, we would join it. However, babies do not nurse continuously. They nurse a little, stop, look around, and resume nursing. Therefore, it does not join.

Teshuvas Zera Avraham Yitzchaki (3, brought in Yabi'a Omer, ibid.): Early Meforshim brought a proper proof from Kerisus to exempt. Ginas Veradim wanted to prove oppositely. I disagree. We see that most babies do not interrupt in the middle. Even if they did, since this is normal, it joins. Why is stopping to look around different than interrupting drinking coffee to talk to someone? Who says that a baby delays more than the time to drink coffee?

Aruch l'Ner (Kerisus 13a DH Safek): The Ri Korkus rejected the proof from Kerisus. Chachamim were more stringent about Tum'ah. A Berachah Acharonah depends on how one benefits.

Hilchos Ketanos (1:9): I support those who say to bless after coffee, for some say that the Shi'ur of time for liquids is like that for food. Talmidei R. Yonah say to bless even without a Shi'ur. (Therefore, it is like a Sfek-Sefeka, i.e. two doubts - PF.) Some say that (we bless) because this is the normal way to drink it. This is wrong.

Mani'ach: My grandfather (Maharam Galanti) would say a Berachah Acharonah, even though the Rambam (regarding a baby) holds that we do not join swallows. The Shulchan Aruch (YD 81:7) says that an adult who nurses is lashed mid'Rabanan; we lash mid'Rabanan for Chetzi Shi'ur. Shirei Keneses ha'Gedolah says to bless, and this is the custom. We are not concerned lest the Rabim err, especially when they have whom to rely on. When the Halachah is unclear, follow what people do.

Yabi'a Omer (ibid.): Our custom is not to say a Berachah Acharonah on tea or coffee, since one does not drink a Revi'is at once. If one let a Revi'is cool off, and drank it at once, what is the law? The Ritz Gei'us and Me'iri (Chibur ha'Teshuvah p.461) rule like the Rambam, that liquids join the time to drink a Revi'is. The Mechaber (OC 612:10, regarding Yom Kipur) rules Stam like the Rambam, and adds that some hold like the Ra'avad's opinion. The Halachah follows what he wrote Stam. It is normal to drink hot coffee a little at a time, and often one delays more than Kdei Achilas Pras, therefore, one does not bless afterwards. However, since this is normal, one who drinks it normally blesses afterwards! Ginas Veradim supported this. The Pri Chodosh (Mayim Chayim 1) rejected it, for we are Metaher a baby that nursed a Revi'is in more than Kdei Achilas Pras, even though it is normal to nurse slowly. The Rambam rules like this. Tosefes Yom ha'Kipurim (80b DH uv'Yemei) and the Mishneh l'Melech (Hilchos Berachos 3:12) brought this proof.