May One Kasher a Microwave Oven Back and Forth for Dairy and Meat?

Is it permissible to use a microwave oven for both milchigs (dairy) and fleishigs (meat), if one kashers it back and forth?

The Magen Avraham (509:11) writes that the accepted minhag is not to use the same utensil for both milchigs and fleishigs even if one kashers in between. The concern is that one might forget the current status of the utensil and inadvertently use it for fleishigs when it is milchigs or vice versa. The Aruch Hashulchan (509:10) disagrees with the Magen Avraham and argues that we do not currently have the proper level of Rabbinic authority to institute new prohibitions. Rav Moshe Feinstein (Igros Moshe, Yoreh De’ah I:43:6) supports the Magen Avraham and maintains that establishing a minhag does not require Rabbinic authority. Furthermore, Rav Moshe (Igros Moshe, Yoreh De’ah III:25) suggests that it may be an actual prohibition to have only one utensil and use it for dairy and meat, although kosherized between uses. This is based on the Gemara in Chulin 8b that a butcher must have separate knives for cutting kosher meat and forbidden fats. Since these knives are used regularly, we cannot assume that the butcher will remember to clean them in between uses.

The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt”l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.