Swallowing the food after the blessing prior to talking or switching rooms:
It is forbidden to make an interval between a blessing and the eating, even while one is still chewing, until he swallows the food. This applies even regarding speaking of matters that pertain to the meal. One likewise must beware not to switch areas while chewing, prior to swallowing. If he spoke of matters not relating to the meal while chewing, it is questionable whether he must repeat the blessing. [Practically, Safek Brachos Lihakel, and a blessing is not to be repeated. However, after swallowing the piece, one should say Shehakol over a piece of candy or bit of sugar and have in mind to exempt the bread with this blessing. Once one has swallowed any amount of the food after the blessing, an interval may be made.]
Bread: Some Poskim rule that one [who is eating a meal] is to eat a Kezayis of bread simultaneously after Hamotzi [without making an interval in-between]. Other Poskim rule this is not necessary and so is the custom. [Thus, according to Admur, as soon as one swallows any amount of bread he may speak. However, other Poskim rule it is proper to suspect for the first opinion.]
One may not talk or switch rooms after the blessing until he swallows the food. Nevertheless, if he did so, a blessing is not repeated. However, after swallowing the piece, one should say Shehakol over a piece of candy or bit of sugar and have in mind to exempt the bread with this blessing. Once one has swallowed any amount of the food after the blessing, an interval may be made.
May one who said a blessing spit out the food if he does not like it, or realized he should not be eating it?
May one answer Kaddish/Kedusha prior to swallowing the food?
If one is sucking a candy or chewing gum, when may he begin to talk?
 If he entered a Revius/Kezayis into his mouth: See Admur Seder 8/11 and Luach 8/12 that tasting a Revius or more requires a blessing even without swallowing. This implies that if he enters a Revius of food into his mouth and tastes it, then he may talk before swallowing. Vetzaruch Iyun!
 Admur 167/9; Kaf Hachaim 167/45; Shaar Hatziyon 167/28; Birchas Habayis 1/14 adds one should not walk even within the same room more than two Amos
The reason: As walking from one place to another is also considered an interval. [Admur ibid]
 Admur 167/9 “It is possible that he must repeat the blessing”; Seder, Luach, M”A, Shelah, Olas Tamid ibid; M”B 167/35
The reason: As the blessing is only on the swallowing and not on the chewing, as one who chews and does not swallow does not need to say a blessing. [Admur 167/9; See also Seder 8/11, Luach 8/12 that “Benefit is considered the benefit of one’s stomach [i.e. swallowing]; second opinion in Michaber 210/2; Tosafus Brachos 14a in name of Rabbeinu Chananel in interpretation of Braisa “Tasting does not need a blessing”; Rosh 2/6 [see Beis Yosef] M”A 211/7 and 10 that this is the main opinion] Thus, if one speaks before swallowing it is as if he spoke between the blessing and eating, and another blessing is required. On the other hand, perhaps the chewing is considered the beginning of the eating and hence it is not considered an interval. [See Shaar Hatziyon 167/30; Halachos Ketanos 2/33; Admur 432/7 regarding talking in middle of Bedikas Chameitz] Likewise, perhaps swallowing is only required when one intends to merely taste the food, while by one who desires to eat the food then swallowing is not required. [Halachos Ketanos brought next]
Other opinions: Some Poskim rule the blessing is not required to be repeated, as tasting the food in one’s mouth suffices, and the only reason why by taste we exempt one who does not swallow is because his intent is to taste. [Halachos Ketanos 2/33; Leket Yosher p 39; Meiri Brachos 40a; Erech Hashulchan 167/3; Tal Oros p. 4; Mor Uketzia 210; Kol Gadol of Maharam Chaviv 10; Bigdei Yesha; Magen Giborim; Chayeh Adam 49, brought in M”B 167/35; See Yabia Omer 5/16] Other Poskim rule one is required to repeat the blessing. [Elya Raba, brought in Shaar Hatziyon 167/30; Beis Menucha 2, brought in Kaf Hachaim ibid]
 Ben Ish Chaiy Emor 14; Shaar Hatziyon 167/30; Kaf Hachaim 167/45; Ketzos Hashulchan 37 footnote 24
 Ketzos Hashulchan 37 footnote 24
 M”B 167/35; See Admur in 168/7, Seder 8/10, Luach 2/11 that any amount of eating requires a blessing, and hence once any amount is swallowed there is no longer an interval involved.
 Admur 167/4; See Kaf hachaim 167/15; Piskeiy Teshuvos 167/14
 1st opinion in Admur ibid; 1st opinion in Yerushalmi Brachos 6/1; 1st opinion in Rokeiach 329; Implication of Rama 167/1 who says one must distribute a Kezayis to each eater; M”A 167/7 learns from Rama that it is an obligation to eat a Kezayis and M”A concludes that one is initially to be stringent like this opinion; Bach 475; Olas Tamid 167/11; Arizal in Shaar Hamitzvos Parshas Eikev; Yifei Laleiv 167/2; M”B 167/35 concludes it is proper to follow this opinion; Vetzaruch Iyun if Admur learns this opinion to require a Kezayis in all situations, or only when eating with others.
 See Degul Merivava 167 and Kaf Hachaim 167/15 brought in coming footnotes; However, see Piskeiy Teshuvos ibid for other reasons why one should eat a Kezayis without interval which would apply to any eater
 Olas Tamid 167/11; Machatzis Hashekel 167/16 learns from a combination of rulings in M”A 167/7 and 167/16 that one is not to talk until he swallows a full Kezayis; M”B 167/35 concludes it is proper to follow this opinion not to talk until one swallows a Kezayis unless in a time of need; Kaf Hachaim 167/15 and 45
 The reason: As less than a Kezayis is not considered eating. [Olas Tamid 167/11; Kaf Hachaim 167/15] This opinion implies that Hamotzi may only be said over a Kezayis of bread, in clear contradiction to the ruling elsewhere [Admur 168/7 and 167/4; Seder 8/10 and Luach 2/11 regarding Bracha Rishona; Michaber 168/9; 210/1; Yerushalmi Brachos 7/1; Rambam Brachos 3/12] that Hamotzi may be said on any amount. The Degul Merivava 167 addresses this question and states that the intent of this ruling is not to say that perhaps only a Kezayis requires a blessing of Hamotzi, but rather that perhaps in order for the blessing of Hamotzi to cover an entire meal, one must eat a Kezayis of bread. On this the Machatzis Hashekel ibid states that it must initially be eaten without interval. Thus, the above ruling of the stringent opinion is only relevant when eating a meal, and not if one simply wants to taste a piece of bread. [So concludes Degul Merivava ibid; Shulchan Hatahor 167/4 and 177/1; Kaf Hachaim 167/15] However, Admur ibid implies that a) the entire discussion of Rama 167/1 is only regarding laws of Derech Eretz and not Brachos, and hence one is to eat a Kezayis simultaneously due to Derech Eretz and b) This law only applies when eating with others. Vetzaruch Iyun! See Ashel Avraham Butchach 167 that the reason is in order to approximate the blessing of Netilas Yadayim to the Kezayis
 2nd opinion in Admur ibid; 2nd opinion in Yerushalmi Brachos 6/1; 2nd opinion in Rokeiach 329, brought in Beis Yosef 167; Opinion in M”A ibid and that so is the custom [however he personally concludes to be stringent]
 The reason: As Hamotzi may be said on any amount of bread. [Admur ibid]
 Ketzos Hashulchan 37 footnote 22 that so is implied from Admur. This is implied from Admur 176/4 who rules the custom is like the 2nd opinion and from Admur 167/9 who omits this ruling of the M”A
 Machatzis Hashekel 167/16; M”B 167/35 concludes it is proper to follow this opinion not to talk until one swallows a Kezayis unless in a time of need; Kaf Hachaim 167/15 and 45
 Admur 167/9; Seder 9/1; Luach 6/1; M”A 167/16; Shelah Shaar Haosiyos Kuf; Ketzos Hashulchan 37/7; If however he initially had in mind to simply taste the food and spit it out after saying the blessing then it is a blessing in vain according to all. [Seder 8/11, Luach 8/12; Michaber 210/2; M”A 211/7; Tosafus Brachos 14a in name of Rabbeinu Chananel in interpretation of Braisa “Tasting does not need a blessing”; Rosh 2/6]
If he entered a Revius/Kezayis into his mouth: See Admur Seder 8/11 and Luach 8/12 that tasting a Revius or more requires a blessing even without swallowing. This implies that if he entered a Revius of food into his mouth and tasted it, then he may talk before swallowing. Vetzaruch Iyun!
 See Kaf Hachaim Yoreh Deah 89/6 regarding if said blessing on milk within six hours of meat; Admur 299/3 regarding if said blessing
 As spoiled food that is inedible does not receive a blessing [Admur 204/2; Seder 7/22; Ketzos Hashulchan 50/2], and hence even if he were to swallow it, it would still be a blessing in vain.
 Levushei Mordechai Kama 29; See Piskeiy Teshuvos 167/13 footnote 94
The reason: As this may possibly cause the blessing to be in vain, as explained above.
Other opinions: Some Poskim rule one may stop to answer Kaddish/Kedusha prior to swallowing the food, as in such a case one may rely on the lenient opinions. [Birchas Habayis 1/15; Yabia Omer 5/16]
 Yabia Omer 5/16; Piskeiy Teshuvos 167/13 footnote 94