Gemara

(Abaye): Even though attached Terumah really is Terumah, we never find that one is liable Misah bi'Ydei Shamayim or adds a fifth for eating it. If one eats it while it is attached, Batlah Daito Etzel Kol Adam (this is abnormal). It is not considered eating!

Krisus 12b (Mishnah) Question: How long can one delay while eating (Isur, and still be liable)?

Answer #1 (R. Meir): He can delay like one who eats crumbs (of parched grain);

Answer #2 (Chachamim): (He is liable) only if the delay from beginning to end was bi'Chdei Achilas Pras (within the time needed to eat half a standard loaf, i.e. the volume of three or four eggs).

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. If one drank intermittently, he becomes Tamei only if he finished bi'Chdei Achilas Pras of when he began.

Pesachim 44a (Rav Dimi): Chachamim (who hold that Heter does not join with Isur to a Shi'ur) exempt for eating Kutach (a dip made with bread crumbs), for one does not normally eat a k'Zayis of Chametz bi'Chdei Achilas Pras:

If he eats it straight, Batlah Daito Etzel Kol Adam.

If he eats it as a dip, he will not eat k'Zayis bi'Chdei Achilas Pras.

Rishonim

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 Krisus we say that the Shi'ur even for drinking is Kdei Achilas Pras. Also the Tosefta in Pesachim says so.

Rambam (Hilchos Berachos 3:12): One says a Berachah Acharonah on a liquid only if he drank a Revi'is.

Kesef Mishneh: The Rambam says so because we find that the Shi'ur for drinking Isurim is a k'Zayis. Regarding food, we find that the Shi'ur for Isurim and Berachah Acharonah is the same (a k'Zayis).

Rambam (Hilchos Ma'achalos Asuros 14:11): If one melted Chelev and drank it hot and burned his throat, or ate raw Chelev, or ate an Isur that rotted and was Batel from human consumption, he is exempt.

Rashi (Pesachim 44a DH Batlah): Eating Kutach straight is not considered (normal) eating to be liable.

Tosfos (Nazir 36b DH Hanach): If one ate it straight, he is liable. Chachamim discussed only what is normal.

Poskim

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

Tosefes Yom ha'Kipurim (80b DH v'Kivan): One may not rely on the Ra'avad to bless after coffee, for usually one does not drink a Revi'is within Kdei Achilas Pras. Even if one does, Gedolei ha'Poskim, i.e. the Rambam, Ritz Gei'us and Tur, all disagree. Shirei Keneses ha'Gedolah says that we cannot learn from Yom Kipur, for that depends on what settles one's mind. Had the law been taught only regarding Yom Kipur, I would agree. However, the Rambam writes it also regarding Isurim, which depend on Hana'ah of the throat and stomach. The Kesef Mishneh says that we learn Berachah Acharonah from Isurim.

Aruch l'Ner (Krisus 13a DH Safek): He also brought a proof from Sukah 42b, which says that we distance from excrement of a baby who can eat a k'Zayis of grain bi'Chdei Achilas Pras. If he eats slower than this it does not join, even though it is normal for him to eat slower. The Ri Korkus said that Chachamim were more stringent about Tum'ah. Berachah Acharonah depends on how one benefits. Also excrement of a baby does not depend on Hana'ah.

Note: I do not understand this proof from a baby at all. We are concerned for a baby old enough that eats at this pace. If he eats slower, this shows that he is too young!

Aruch l'Ner: There is no proof from Kutach. It is only a mixture of Chametz, therefore, if he delays more than the Shi'ur, he does not benefit from Chametz, even if he ate normally. I say that the Rambam agrees that when the Shi'ur for drinking is a Revi'is, it joins within Kdei Achilas Pras. I say that one may bless if he drank a Revi'is of coffee within this time.

Birkei Yosef (204:6, brought in Sha'arei Teshuvah 12): Yad Aharon says 'I saw Anshei Ma'aseh (people of great deeds) leave coffee to cool off, and then they drink it and bless Borei Nefashos.' Batei Kehunah commented that this is not the way to drink it. People do not do like this. Batlah Daito Etzel Kol Adam. This is like we say about Kutach. It is a mistake to distinguish these. See also Menachos 70a. The Anshei Ma'aseh did not fix anything. At least regarding a Berachah, Batlah Daito Etzel Kol Adam.

Sha'arei Teshuvah (12): It is not clear to say Batlah Daito Etzel Kol Adam for a Berachah Acharonah. Even one who drinks water for thirst blesses Borei Nefashos afterwards. Surely this is not a reason to exempt from a Berachah Rishonah. One blesses before any amount! Here people are not so particular to drink coffee that is very hot, so Batlah Daito Etzel Kol Adam does not apply. If so, one who lets a Revi'is cool off a bit and drinks it at once, may bless afterwards. If one is unsure whether he drank within the time to drink a Revi'is, even though Safek Berachos Lehakel (when in doubt, we do not bless), since one can evade the Safek through drinking a Revi'is (at once) or eating something for which the Berachah Acharonah is Borei Nefashos, he should do so, and exempt also the coffee.

Ha'arah on Birkei Yosef (204:7): There was no Hava Amina to exempt from a Berachah Acharonah because it is abnormal. One must bless, for he benefited! Derech Achilah or Shtiyah applies only to an extended eating, with a Shi'ur. This is why Tosfos (39a DH Batzar) was unsure whether Borei Nefashos requires a Shi'ur, because it is not an esteemed Berachah. The Rosh (6:15) was unsure. The Ri holds that since Borei Nefashos is not for an important eating, it is merely thanks. Even though the Halachah does not follow him, it is a proper reasoning.

Nishmas Adam (50:5): Krisus 12b connotes that if something is normally eaten (intermittently), it is not considered a Hefsek. R. Meir says that one can delay like one who eats Kelayos and be liable, and Chachamim say that the delay cannot exceed Kdei Achilas Pras. We conclude that R. Meir is stringent. One is liable even if he ate over a long period of time, like one who eats Kelayos. Why did he teach like one who eats Kelayos? (I.e. he should have given the time, e.g. to eat two loaves!) Rather, he means that it is as if he eats Kelayos; in that case, Chachamim agree. R. Meir holds that this larger Shi'ur of time applies to all foods. If so, if one drinks a hot drink over a long time (like is usual), it joins for a Berachah Acharonah. However, I did not find the Rambam or any Posek distinguish between Kelayos and other foods. Rather, they hold that Chachamim argue even about Kelayos, even though it is normal to eat them slowly. If so, also a hot drink does not join over a long time.

Yabi'a Omer (ibid.): Ginas Veradim brought this proof (from Kelayos); Zera Avraham Yitzchaki (3) rejected it. Ma'aseh Roke'ach says that most Acharonim agreed not to bless a Berachah Acharonah on coffee, and therefore, one who drinks soup with a spoon does not bless afterwards. The same applies to drinks with crushed ice that people drink in summer. One who drinks them must pause many times in the middle. One does not bless after them. I would add that Borei Nefashos is not an absolute full Chiyuv. The Gra (Hagahos on Yerushalmi Berachos 6:4) says that in the days of the Mishnah, they did not bless it. When Rav Ashi remembered, he would bless on everything (even water - Berachos 44b). Therefore, surely when there is an argument one should be passive and not bless.

Chasan Sofer (4): The Eshel Avraham (210:1) says that if one ate bread to satiation, the Torah obligates him to say Birkas ha'Mazon even if he did not eat a k'Zayis bi'Chdei Achilas Pras. Likewise, we exempt from a Berachah Acharonah one who drank a Revi'is in more than the Shi'ur of time, but if one drank until he was satiated with drinking and does not want to drink more, he blesses afterwards even if he delayed a long time. This is why my grandfather (the Chasam Sofer) would bless after coffee.

Rebuttal (Yabi'a Omer (ibid.): Many disagree with the Pri Megadim.

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.

Kaf ha'Chayim (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. 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. The Birkei Yosef says that it does not help to leave a Revi'is to cool off. I say that one should exempt it through something else, and all the more so if he drank it cold. However, some leave tea to cool off and drink it to quench their thirst, in place of water. All agree that one blesses afterwards if he drank a Revi'is at once.

Yabi'a Omer (5 OC 18): Many Acharonim say that if one drank a Revi'is of coffee (when it was lukewarm) at once, we do not say Batlah Daito Etzel Kol Adam. One who blesses has whom to rely on. In any case, if one asks, we tell him not to bless, for many Acharonim, especially Sefardim, say Batlah Daito Etzel Kol Adam. It is better to be passive, and Safek Berachos Lehakel.