OU KASHRUT RABBI EZRA FRIEDMAN PAGE BY Director, The Gustave & Carol Jacobs Center for Kashrut Education
Kashering a Microwave for Pesach Basic Principle of Kashering:
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he basic principle in kashering any utensil in general (year round) is “k’bolo kach polto,” food flavor releases the same way it absorbs. [Literally – “spits the way it swallows”]. This principle teaches us that in order to remove the flavor of a food we have to use the same means with which the food was absorbed. For example, if non-kosher food is cooked in a pot in water, the utensil is kashered by immersing the pot in boiling water to remove the non-kosher flavor. Similarly, a barbeque rack absorbs heat through direct flame without any contact with water. According to “k’bolo kach polto,” a bbq rack is therefore kashered by flame. What is the necessary procedure for kashering a utensil used for various types of cooking? For example, if a skewer is used both in liquids and on an open fire, how should it be kashered? The answer is disputed amongst halachic authorities. The Rashba (Responsa 1:372) holds that 44
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we kasher by the majority use, meaning if the utensil was mostly used with boiling liquids then it should be kashered with boiling water. If the utensil was mostly used with direct flame, it is kashered through flame. This concept of majorityuse is called “rov tashmisho.” The Raavyah (Issur V’heter 58:45-46) however, disagrees. He brings proof to kasher by the method of the utensil’s minority use. The Raavyah bases his opinion on the concept of “miut tashmisho.” Thus kashering is carried out by the minority- use, if it is the more stringent method. A classic case where the Rashba and Raavyah disagree is plates that are normally used for cold food, yet are occasionally used for hot foods. According to the Rashba, we can be lenient and rely on the majority use, and suffice with washing in cold water. In contrast, the Raavyah would be stringent and require boiling water to kasher the plates.
In a microwave, the main absorption of flavor is through steam The Shulchan Aruch, (OC 451:6), which sets Sefardic custom, rules like the Rashba, while the Rema (Ibid) is stringent like the Raavyah. The consensus amongst
