A Beracha Aharona is required after eating only if one ate the quantity of a "Ke’zayit" within a certain time-frame called "Kedeh Achilat Paress." (In other editions of Daily Halacha, we discussed the precise definitions of these terms.) The question arises as to whether a Beracha Aharona is required if one went outside after eating less than a "Ke’zayit," and then returned and ate some more, such that he ended up eating a "Ke’zayit" within the period of "Kedeh Achilat Paress." On the one hand, since he ate a "Ke’zayit" within this period, he should seemingly be required to recite a Beracha Aharona. On the other hand, one might argue that since he ate the amount of a "Ke’zayit" in two separate sittings, and did not eat a whole "Ke’zayit" in a single sitting, the Beracha is not required. Indeed, when he returns, he is required to recite a new Beracha before resuming his eating, since his departure effectively "ends" the original Beracha he recited. This would seem to suggest that in such a case, we view the two sittings as separate from one another, and so perhaps we might conclude that we do not combine the two stages of eating, and thus no Beracha Aharona is recited.
However, the Mishna Berura (Rav Yisrael Meir Kagan, 1839-1933) rules (210:1) that one indeed recites a Beracha Aharona in such a case, despite the fact that the eating was briefly interrupted when the person left. As long as one ate a "Ke’zayit" within the time frame of "Kedeh Achilat Paress," he recites a Beracha Aharona, even if he had left after eating less than this amount and then returned and ate the rest. This is also the ruling of the Kaf Ha’haim (Rav Yaakob Haim Sofer, Baghdad-Jerusalem, 1870-1939), and of Hacham Ovadia Yosef (listen to audio recording for precise citation, and see Yalkut Yosef, English edition, Berachot, p. 244).
Summary: If one ate less than a "Ke’zayit" of food, left, and then returned and ate some more for a total of a "Ke’zayit," then as long as the entire "Ke’zayit" was eaten within the period of "Kedeh Achilat Paress," he recites a Beracha Aharona.
