Question: Is it permissible to drink coffee which was prepared by a non-Jew, such as the coffee served during flights aboard non-Jewish airlines, or does this constitute the prohibition of foods cooked by a non-Jew or any other prohibition?
Answer: Clearly, the coffee sold in many places where non-Jews reside outside of Israel contains ingredients which pose several other serious Kashrut concerns; we are therefore not even discussing the Kashrut status of coffee with all sorts of creams or which have different flavors mixed into them. We are only discussing a basic coffee made from coffee granules, sugar, and water.
What we must discuss with is the edict of our Sages forbidding us from consuming foods cooked by a non-Jew, as we have explained in previous Halachot. We have also discussed that anything which can be eaten raw or uncooked, such as apples, is not included in this prohibition. Only things which can only be eaten cooked, such as potatoes, are included in this prohibition. It is therefore permissible to drink water boiled by a non-Jew, for water is drinkable even cold. Thus, the decree regarding foods cooked by a non-Jew does not apply here.
Regarding coffee, although there are different ingredients mixed into the water, such as coffee grains and sugar, its blessing is nevertheless “Shehakol” because it is primarily water and we do not recite the “Boreh Peri Ha’etz” blessing on this beverage because of the coffee beans mixed into it. If so, the coffee granules and sugar mixed into the water are considered merely secondary to the water, which is considered the primary ingredient of this beverage. The coffee granules, therefore, do not pose a concern of the prohibition of foods cooked by a non-Jew to prohibit the entire beverage.
Similarly, the Tosafot in Masechet Avodah Zara (31b) write that beer brewed by non-Jews is not prohibited due to the injunction of foods cooked by a non-Jew, for the blessing on beer is “Shehakol” and not “Mezonot.” Therefore, the barley mixed into the beer is considered secondary to the entire beverage and there is no reason to prohibit the entire beverage because of the edict of foods cooked by a non-Jew. (It is nevertheless forbidden to drink beer brewed by a non-Jew at a non-Jewish party due to a different rabbinic decree, as discussed in the aforementioned Gemara.)
If so, the prohibition of foods cooked by a non-Jew does not apply to coffee. The Radbaz rules likewise in one of his responses and concludes by saying that in any event, one should not drink coffee at non-Jewish parties for this can lead to many other issues.
Maran Rabbeinu Ovadia Yosef zt”l deals with this matter at length in his Responsa Yechave Da’at (Volume 4) and he quotes several other reasons for leniency as well as stringency in this matter. He concludes by saying that, halachically speaking, this is not included in the prohibition of foods cooked by a non-Jew; however, one who acts stringently in accordance with the more stringent opinions is especially praiseworthy.
Nevertheless, he discusses another possible Kashrut problem that may arise by drinking coffee on a non-Jewish airline which is that the coffee is served in non-Jewish utensils which commonly have boiling non-Jewish milk poured into them. Since drinking milk of a non-Jew is forbidden, utensils which have absorbed the taste of the non-Jewish milk thereby prohibit anything poured into them. It will therefore be prohibited to drink coffee on a non-Jewish airline unless one knows that the utensil he is drinking out of does not have this issue, such as if the coffee is served in a disposable cup or in a glass mug (which does not absorb flavor) and the like.
Nonetheless, Maran zt”l writes that when there is a pressing need, one may rely on several leniencies which he quotes and one may even drink the coffee even out of porcelain mugs and the like. This only applies though when no other alternative is available; however, if one can request that he be served coffee in a disposable cup or in a glass mug, one must do so.
Summary: Coffee which contains no other ingredients which may pose Kashrut concerns may be drunk even if it was prepared by a non-Jew as long as it was poured into a disposable cup or a glass mug. If such a cup is unavailable there are leniencies with regards to drinking out of porcelain mugs and one may rely on these opinions when necessary. One who acts stringently and abstains from drinking coffee prepared by a non-Jew is especially worthy.