Until “Yitbarach”
Maran Ha’Bet Yosef (Chapter 56) quotes the Midrash, “Rabbi Elazar son of Rabbi Yose said: Once, I was travelling on the way, and I met up with Eliyahu Ha’Navi z”l who had four-thousand loaded camels with him. I asked him, ‘What are they loaded with?’ To which he replied, “They are loaded with wrath and fury to seek revenge with wrath and fury from those who speak between Kaddish and “Barechu” (found in the Shacharit prayer before the blessings of Keri’at Shema), between one blessing and another (of the blessings of Keri’at Shema), between one paragraph and another (of Keri’at Shema), or between “Amen Yehe Shemeh Rabba” etc. and “Yitbarach.”
Maran Ha’Bet Yosef infers that since it is forbidden to speak between “Amen Yehe Shemeh Rabba” and “Yitbarach,” one must indeed recite the word “Yitbarach.” Rabbeinu Yosef Gikatilia writes likewise that one may not separate the words “Almaya” and “Yitbarach.” Maran rules likewise in his Shulchan Aruch that those who answer until “Le’alam Ul’almeh Almaya” alone are mistaken, as one may not separate the words “Almaya” and “Yitbarach.”
The Opinion Not to Recite “Yitbarach”
Nevertheless, there are those who disagree with Maran’s opinion on this matter and write that one should only answer until the word “Almaya” and not recite “Yitbarach.”
Therefore, some say that if one finds himself in a prayer during which one may not speak, such as Keri’at Shema and its blessings, although one would stop to answer Amen to Kaddish, one should only recite until the word “Almaya” and not recite the word “Yitbarach,” for since this matter is subject to a disagreement among the Poskim and there is a doubt whether or not this constitutes an interruption, one should abstain from answering in this manner.
Nevertheless, Maran zt”l writes (in his Yabia Omer Volume 1, Chapter 5, Section 3) that we, Sephardic and Middle Eastern Jewry, who have accepted all the rulings of Maran Ha’Shulchan Aruch, must answer up to and including the word “Yitbarach” during Keri’at Shema and its blessings as well.
Continuing Until the Words “Da’Amiran Be’alma”
Regarding whether one should answer “Amen Yehe Shemeh Rabba” only until the word “Yitbarach” or continue until “Da’amiran Be’alma,” this is also subject to a disagreement among the Rishonim; it seems from the words of Maran in his Bet Yosef that one should answer until the words “Da’amiran Be’alma,” for until the word “Be’alma” there are twenty-eight words and our Sages write (Shabbat 119b), “One who answers ‘Amen Yehe Shemeh Rabba’ with all his might (“Kocho”) merits having the evil decrees against him torn up” and what they meant was to concentrate on all twenty-eight words that the “Amen Yehe Shemeh Rabba” contains. This is indeed the Sephardic custom. On the other hand, Ashkenazim customarily answer until “Yitbarach” based on the opinion of many Rishonim and Acharonim.
Maran zt”l writes that even according to our custom, if one finds himself during a part of the prayer where he may not talk, such as during Keri’at Shema and its blessings, one should only answer until “Yitbarach,” as we have already established. However, if one finds himself in the middle of Pesukei De’Zimra (between Baruch She’amar and Yishtabach), between the paragraphs of Keri’at Shema, or between the blessings of Keri’at Shema, one may indeed answer until “Da’amiran Be’alma.”
Summary: The Ashkenazi custom is to answer “Amen Yehe Shemeh Rabba” until “Le’alam Ul’almeh Almaya Yitbarach.” Our custom, based on the opinion of Maran Ha’Bet Yosef, is to answer until “Da’amiran Be’alma.” If one finds himself in the middle of Keri’at Shema and its blessings, one should answer only until “Yitbarach,” for there is a doubt regarding whether continuing constitutes an interruption.