What if a non-Jew cooked food which is subject to the prohibition of bishul akum, like rice, and then dries-out the food? In this case, is this food considered to be bishul akum and therefore prohibited?
The Ben Ish Hai (Parashat Hukat, Shana Bet 17) relates that in Bagdad, non-Jews would cook bulgur until it was edible, and then they would dry it out, and sell it to Jews. The Ben Ish Hai was asked whether this burgul was considered to be cooked, in which case it was prohibited due to the prohibition of bishul akum, or since the Jew would need to re-cook it, it would be permissible. The Ben Ish Hai cites a responsum from the Avkat Rahel, the teshuvot authored by R. Yosef Karo, where he rules that if the non-Jew dries out the food, the originally cooking is undone, and therefore, in this case, the burgul would be permitted.
This question is relevant nowadays, as many precooked rice and soups, which were cooked in a factory by non-Jews, are sold as "instant" foods which can be consumed after one adds hot water. According to the Ben Ish Hai, the prohibition of bishul akum would not apply to these foods. The Ben Ish Hai notes that this leniency may also lead to stringency as if a Jew cooked burgul, and then other Jews wished to buy the precooked burgul and ask their non-Jewish workers to re-cook it, in this case, the food would be prohibited due to bishul akum.
Summary: When food is cooked by non-Jews, and then dried-out and cooked by Jews, this food is not subject to bishul akum and is permitted.
