The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Balak (11; listen to audio recording for precise citation), discusses the case of a person who began reciting a Beracha with the intention of reciting the wrong Beracha. For example, an individual prepares to eat a watermelon, which requires the Beracha of "Ha’adama," and he initially thinks that he should recite the Beracha of "Ha’etz." He begins reciting "Baruch Ata Hashem Elokenu Melech Ha’olam" planning to conclude with "Boreh Peri Ha’etz," but before concluding the Beracha he remembers that the correct Beracha is "Ha’adama," and he concludes the Beracha properly. Does his mistaken intention during the first part of the Beracha disqualify the Beracha, or is his Beracha valid since he did, after all, recite the correct text?
The Ben Ish Hai writes that according to the majority view among the Halachic authorities, the person’s Beracha is valid in this case, since, as mentioned, he recited the correct Beracha. This would also apply to a case where a person prepared to eat a food requiring "She’hakol" and initially thought that it requires "Ha’etz." If by the time he concluded the Beracha he remembered to recite "She’hakol Niheya Bi’dbaro," then his Beracha is valid even though throughout the first part of the Beracha he had planned to recite "Ha’etz." Another case where this Halacha applies is where a person picked up a cup of water thinking it was wine, and began reciting the Beracha with the intention of concluding "Boreh Peri Ha’gefen." So long as he ultimately realized his mistake and recited the correct Beracha over water – "She’hakol" – he has fulfilled his obligation.
Furthermore, the Ben Ish Hai writes, even if a person recited the wrong Beracha, but within several seconds he immediately corrected his mistake and recited the proper Beracha, he has fulfilled his obligation.
However, as the Ben Ish Hai notes, this ruling is not universally accepted. The Rambam (Rabbi Moshe Maimonides, 1135-1204) held that if a person recited the primary segment of the Beracha ("Baruch Ata…Elokenu Melech Ha’olam") with the intention of reciting the wrong Beracha, the Beracha is invalid. In his view, a person’s intention while reciting the first part of the Beracha affects the status of the Beracha, and therefore even if he realizes his mistake before completing the Beracha and recites the correct conclusion, his Beracha is disqualified. Thus, for example, if a person began reciting a Beracha over a cup of water thinking it was wine, then according to the Rambam, his Beracha is invalid even if he realized his mistake toward the end of the Beracha and recited the proper conclusion of "She’hakol."
The Ben Ish Hai therefore advises a person in this situation to take a sip of the drink, so that his Beracha will not have been recited in vain, and then share the drink with somebody else and have him recite the Beracha. He should listen to that person’s Beracha with the intention of fulfilling his obligation in order to satisfy the Rambam’s view, and he may then resume eating according to all views.
Summary: If a person began reciting a Beracha over a food or drink with the intention of reciting the wrong Beracha, but realized his mistake before the end of the Beracha and recited it correctly, his Beracha is valid according to most authorities. Preferably, however, he should take a small sip or bite, and then give some of the food or drink to somebody else and listen to that person’s Beracha, so that he could continue eating or drinking without concern according to all views.
