The Mishna in Avodah Zarah (35b) teaches that there is a prohibition to eat any food cooked by a non-Jew. Later, the gemarah (27b) relates this prohibition to the pasuk, ” Ochel bakesf tishbereini ve’achalti umayim bakesef titen li veshatiti” (Devarim 2/28), “you will supply me food in return for money and I will eat, and you will give me water in return for money and I will drink”. Initially, it is assumed in the gemarah that we learn from the pasuk, “ as water from the gentiles is drunk, unaltered by fire, so too the food you eat from the gentiles may not be food processed in fire (cooked)”. The gemarah later clarifies, since fire is not mentioned in the pasuk, there is no biblical prohibition only a rabbinic one supported indicatively by the pasuk (an asmachta).
Since the prohibition is rabbinic in origin, the Rabbis also limited its parameters. One such limitation is quoted in Shulchan Aruch Yoreh Dayah (113/13). Food processed through salting or smoking is not considered cooked. The Ramah then adds that pickled food is not prohibited since only cooking with fire is prohibited. This halacha in the Shulchan Aruch and Ramah leads to an interesting modern day question: What is the status of food cooked by a non-Jew in a microwave oven?
Rav Shemuel Vosner in his Shevet Halevi (vol.8 res.185) sees it as obvious that food cooked by a non-Jew in a microwave is prohibited. Rav Vosner reasons that microwave cooking is an act of cooking, as opposed to salting, smoking or pickling which does not constitute an act of cooking. Since food cooked in a microwave is in fact cooked and the act could lead to unwanted close relations with non-Jews or to eating non-Kosher food, it falls into the realm of that which is prohibited.
In a similar vein, Rav Sterenbuch in his Teshuvot ve’Hanhagot (vol. 5 res. 249) writes that even if microwave cooking is not technically considered cooking, for the purpose of the prohibition of gentile cooking it is defined as cooking. His reasoning is that for the purpose of non-Jewish cooking anything that people relate to as cooked, regardless of how it was cooked, constitutes cooking.
In counter distinction, Rav Asher Weiss in Minchat Asher (Devarin siman 5 sec. 6) contends that microwave cooking does not fit the definition of the Ramah’s “bishul shel esh”, cooking by fire. Furthermore, even if we see microwave cooking, for other purposes, as cooking, since it is an inferior form of cooking, not used when quality cooking is required, it is not included in the prohibition of non-Jewish cooking. Yet, in practice, he suggests that only if there is monetary loss by not allowing a non-Jew to cook with a microwave or some other great need, a gentile should be allowed to cook using a microwave.
It would seem that the core of this disagreement is on how to read the Shulchan Aruch and Ramah. Do we focus on the examples of salting, smoking and pickling distinguished from cooking by lack of heat and by the form of change which takes place? Or, do we focus on the words “bebishul shel esh”, cooking by fire, excluding any non-fire sourced cooking.