Kashering a Microwave for Pesach

by Rabbi Kassel Abelson, 1983; Edited by Rabbi Robert Binder

Question (Sh’eilah)

How can a microwave oven be koshered for Passover use?

Answer (Teshuvah)

In Exodus 12:15-20, the Torah prohibits the eating and ownership of hametz (“leavened bread,” defined as food prepared from five species of grain that has been allowed to leaven), during Passover. This requires removing all hametz and admixtures of hametz from the home and kashering utensils before the festival begins. In addition to pots and pans being kashered or replaced with Passover-only vessels, the entire kitchen, including the sinks, stovetop and oven – wherever there may have been contact with hametz – must be thoroughly cleansed and kashered.

There is a basic principle applied to kashering utensils for Passover: kevoleo kakh poleto (“as the vessel absorbs, so does it rid itself of what is absorbed”) [Pesachim 30b]. Thus, utensils used for cooking may be kashered by boiling water. Glassware may be soaked in water for a period of time, while utensils used for broiling over an open fire must be heated until they are red-hot. Ovens are thoroughly cleansed and then heated until they are red-hot, a process known as libbun.

A microwave oven does not fit into any of the conventional categories. Though it is called an oven, it is in reality a protective box whose function is to safeguard people from the harmful effects of radiation. The box is made of steel and coated with a nonporous and therefore nonabsorbent plastic. The inside surface of the microwave oven, unlike that of a conventional oven, remains cool during the cooking process. Only in the spot where the utensil containing the food is placed does the surface become somewhat warm, because it absorbs some of the heat from the utensil as the food cooks.

Hence, the traditional method of cleansing an oven though libbun would not be necessary in the case of a microwave oven. Instead, the principle of kevoleo kakh poleto would suggest a method of kashering a microwave oven that would involve a thorough cleansing of the interior. In order to differentiate Passover kashering from ordinary cleaning, it is recommended that a bowl containing water be placed in the microwave interior and the oven be turned so that the water boils and steam reaches all the interior parts of the microwave oven.

N.B. This procedure of kashering does not apply to microwave ovens that have a browning element.