If a person who had been eating or drinking recites a Beracha Aharona, would he recite a new Beracha if he continues eating or drinking? For example, if a person drinks a large glass of water, and in the middle, for whatever reason, he recites "Boreh Nefashot," must he recite a new Beracha of "She’hakol" before he resumes drinking?
The Rashba (Rabbi Shlomo Ben Aderet of Barcelona, Spain, 1235-1310) addresses a specific case where this question arises, in the context of the Seder on Pesah. When a person recites the Beracha of "Boreh Peri Ha’adama" over the Karpas at the Seder, that Beracha applies as well to the Marror which he will eat later during the Seder. The Rashba discusses the case of a person who recited "Boreh Nefashot" after eating the Karpas, and rules that he would be required to recite "Ha’adamah" over the Marror. According to the Rashba, the Beracha Aharona in essence "stops" the Beracha recited over the Karpas, and does not allow it to cover foods eaten subsequently. Even though this individual certainly knew that he would eat Marror later in the Seder, and thus cannot be said to have diverted his attention from the Beracha, nevertheless, the recitation of the Beracha Aharona itself terminates the efficacy of the Beracha.
The Peri Hadash (Rabbi Hizkiya Da Silva, 1659-1698) extends the Rashba’s ruling to all cases where one recites a Beracha Aharona: if he wishes to continue eating, he must recite a new Beracha. For that matter, if one wishes to resume eating after reciting Birkat Ha’mazon, too, he would be required to recite a new Beracha before he eats. This is the ruling of numerous authorities, including Rabbi Moshe Halevi (Israel, 1961-2001), in his work Birkat Hashem (vol. 3, Siman 11).
The exception to this rule is a case where a person recited the Beracha either unwittingly, or without realizing that it ends the applicability of his Beracha. The Magen Abraham (commentary to the Shulhan Aruch by Rabbi Abraham Gombiner, Poland, 1637-1683) writes that such a case, where a person either did not intend to recite the Beracha at all, or recited the Beracha thinking that he could still rely on the original Beracha, the original Beracha remains in force. Other authorities dispute the Magen Abraham’s ruling, and Hacham Ovadia Yosef, in his work of responsa Hazon Ovadia, applies to this case the famous rule of "Safek Berachot Le’hakel" – meaning, one should not recite a Beracha in situations of doubt. Hence, in this situation one may resume eating without reciting a Beracha.
Interestingly, Rabbi Moshe Halevi writes that one may not resume eating in this case. While it is true that the person cannot recite a Beracha, in deference to the view of the Magen Abraham, he must also take into account the other view, according to which he may not eat without reciting a Beracha. According to Rabbi Moshe Halevi, then, a person cannot continue eating at that point. Hacham Ovadia, however, disagrees, and allows a person in this case to continue eating without reciting a new Beracha.
Summary: If a person recited a Beracha Aharona (or Birkat Ha’mazon) and then wishes to continue eating, he must recite a new Beracha, unless he had recited the Beracha Aharona unwittingly, or under the mistaken assumption that he would still be able to eat relying on the original Beracha.
