What is one to do if he began drinking a liquid, and then remembered that he did not say a blessing?
One who forgot and entered a drink into his mouth without saying a blessing [and then remembered prior to swallowing it] some Poskim rule he is to swallow the liquid [and is not required to spit it out]. Amongst these Poskim, some rule that he is not to say the before blessing at all over the liquid, even after swallowing. Other Poskim, however, rule that after he swallows the liquid he is to say a blessing. Practically, the Poskim conclude that in order to avoid the disputes, if one has more liquid available, he is to spit it out and say a blessing on the new liquid. [If he does not have more liquid available, then if he needs the drink and does not want to spit it out, he is to think the blessing in his mind, swallow it and not recite a before blessing.] [Other Poskim, however, suggest that in all cases one is to think the blessing in his mind and then swallow the liquid. Practically, one is to follow the former conclusion.] In all cases, even if a before blessing was not said, an after blessing is to be recited [if one drank a Revius].
Food: One who forgot and entered food into his mouth without a blessing must spit it out and say the blessing, if it is a type of food which will not become repulsive to the person after it is spat out. If, however, the food will become repulsive after it is spat out, then one is not required to spit it out and is rather to place the food into one of the sides of his mouth and say the blessing.
Liquid: One who forgot and entered a drink into his mouth without saying a blessing is to spit it out. If, however, he does not have anything more to drink, and desires to drink it, he is to think the blessing in his mind and then swallow it.
 Tur and Michaber 172:1; Brachos 50b
 Michaber ibid; Rama ibid; Tur ibid; Brachos ibid “By liquids one is to swallow it”; Rabbeinu Chananel, brought in Tur ibid and Rosh Brachos 33; Rosh Brachos 33; Rashba Brachos ibid in name of Raavad, brought in Beis Yosef 172; Leaning way of learning Rambam Brachos 8:12
 The reason: As it is not possible to place the liquid on the side of his mouth to allow a blessing to be said, and if he spits it out it will become repulsive. [See Brachos ibid] Alternatively, as once liquid is placed in the mouth it loses its food status as it is no longer fit for drinking. Accordingly, one is not to be particular to recite a blessing even if he could. [M”A 172:1; Rabbeinu Chananel ibid, brought in Rosh ibid; Kaf Hachaim 172:1]
Other Opinions: The Yerushalmi Brachos 6:1 rules that the liquid is to be spat out and not drunk without a blessing. Many Poskim and Mefarshim explain that in truth there is no dispute between the Bavli and Yerushalmi, and while the Bavli refers to a case that one has no more liquid available, the Yerushalmi refers to a case that there are more liquids available. [Raavad, brought in Rashba ibid and Beis Yosef ibid; Maareh Hapanim on Yerushalmi ibid; Amudei Yerushalmi ibid; Bach 172; M”A 172:1; Elya Raba 172:1]
 Michaber ibid; 1st opinion in Tur ibid; Rabbeinu Chananel, brought in Tur ibid and Rosh Brachos 33, in his interpretation of Brachos ibid; Possible way of learning Rambam Brachos 8:12 [See Beis Yosef 172; Kaf Hachaim 172:3]
The reason: As we never say a before blessing after a food has been eaten. [Taz 172:1, as explained in 167:8] Alternatively, once the liquid is in one’s mouth it is no longer drinkable by most people and hence does not deserve a blessing. [M”A 172:1; Rabbeinu Chananel ibid, brought in Rosh ibid]
 Rama ibid “And so is the main opinion”; Darkei Moshe 172:1; 2nd opinion in Tur ibid; Rosh Brachos 33; Rashba Brachos ibid in name of Raavad, brought in Beis Yosef 172; Leaning way of learning Rambam Brachos 8:12 [So learns Darkei Moshe ibid; See Beis Yosef 172]
 The reason: Although we do not say a blessing after a food has already been eaten, since in this case one remembered prior to the swallowing, it is similar to saying the blessing beforehand, even though it is only said after the swallowing, as he has no choice. [Taz 172:1; M”A 172:3; Rosh ibid; See Beis Yosef ibid]
 M”A 172:2 and 3; Bach 172; Elya Raba 172:1; Raavad, brought in Rashba ibid and Beis Yosef ibid, in explanation of Yerushalmi Brachos 6:1 “Liquids are to be spat out”; Ohel Moed 1:12; Maareh Hapanim on Yerushalmi ibid; Amudei Yerushalmi ibid; P”M 172 M”Z 2 regarding wine; M”B 172:2 “And so should be done” however in Biur Halacha 172 :1 “Vieino” he writes “One who is lenient in this is not to be protested”; Ketzos Hashulchan 55:9
 The reason: This is done to avoid the dispute between the above Poskim [M”A ibid] and is also done to avoid the dispute between the Bavli and Yerushalmi. [See Poskim ibid] Rebbe Akiva Eiger on M”A ibid who questions as to what dispute one will enter if he has more liquid in front of him and he thus must spit it out, as he can simply swallow it as agree all Poskim and then say a blessing and drink from the more liquid. This avoids the dispute according to all, and hence it is not understood why the M”A ibid directs one to spit it out.
 Derech Hachaim; Ketzos Hashulchan ibid based on Admur 185:1; See Maareh HaPanim on Yerushalmi ibid that most Poskim, Geonim and Rishonim argue on Rama, and Safek Brachos Lihakel, and hence one is to wallow it without saying any blessing. The Poskim in previous footnote rule that even if one does not have more liquid available, one should only swallow the liquid if he is in need of it. Otherwise, it is best to spit it out in order to avoid the dispute and not benefit from the world without a blessing. [Kaf Hachaim 172:1 and 3]
 P”M 172 M”Z 2; Derech Hachaim; Shulchan Hatahos 172:1; Kaf Hachaim 172:1;
 The reason: As since whatever one does will be under a dispute, it is better in this case to rely on the Rambam Brachos 1:7 who rules one is Yotsei even if he thinks a blessing in his mind. [Poskim ibid]
 See Piskeiy Tehsuvos 172 footnote 18 who questions the above ruling of thinking the blessing, as by doing so one enters into a new dispute as to whether he may say a blessing on the remaining liquid. [See P”M 62 a”a 1; Chayeh Adam 5:16]
 If, however, one followed the Rama ibid and recited a before blessing after swallowing the liquid, then it is questionable if one should recite also an after blessing, as we do not find a before and after blessing said in approximation of each other. Practically, if one ate one of the foods of the 7 Minim an after blessing is to also be said, although if he drank water and other foods it is questionable. [M”A 172:3]
 M”A 172:2; Beis Yosef 172; Nanar Mordechai 172:1; P”M 172 A”A 1; Kaf Hachaim 172:2