Question: Can a household oven be koshered for Pesach?
Answer: Maran zt”l discusses this issue in several of his works (among them Yabia Omer, Volume 5, Yoreh De’ah, Chapter 7) and this issue is a halachically complex one for the flowing reasons:
When foods are being baked or cooked in an oven, the foods release steam that rises and is absorbed by the walls of the oven and the next time other foods are cooked or baked in the oven, the flavor of this steam is released into the food now being cooked. It is therefore obvious that one may not use the same oven for both meat and dairy throughout the year unless the oven is koshered between its meat use and its dairy use.
Similarly, as we have explained in the past, the method of koshering any vessel which absorbed flavor is in the same way that the vessel absorbed the flavor to begin with, as the rule goes, “Just as it absorbs, it releases.” Thus, a metal pot which is used for cooking foods on the fire must be koshered by the process of Hag’ala which is immersing the pot into a bigger pot filled with boiling water on the fire. In this way, the pot will release all of the flavor it has previously absorbed.
Maran Ha’Shulchan Aruch (Chapter 451) writes that vessels used directly with fire must be koshered through fire. This process is called “Libun”. For instance, skewers, which are placed directly on the fire, must be koshered by torching them with fire until sparks begin emerging from the skewer (i.e. until it becomes red-hot). Although when the skewer is being used to grill on the fire it does not reach such a red-hot temperature, nevertheless, its method of koshering is through Libun which is heating the skewer until it is actually red-hot.
Based on this, it would seem that an oven, which works using very high temperatures, should be koshered through Libun which is nearly impossible on a practical level.
Nevertheless, regarding our ovens, the Poskim write that since we do not usually use the actual walls of the oven itself and we merely put foods in pans or trays, the only concern is the steam that spreads within the oven during cooking or baking. Since the oven absorbs the food’s flavor through its steam, its koshering process will likewise be by heating it up to its highest possible temperature and this will be sufficient to kosher it.
However, even this is subject to a disagreement among the Poskim, for some authorities maintain that even such ovens require koshering by actual Libun. Thus, some act stringently and do not kosher their ovens at all; rather, purchase a special oven for Pesach. Others say that even on a practical level, it is extremely difficult to clean out the entire oven to the extent that not even one crumb remains and they do not use these ovens on Pesach unless the oven can reach such a high temperature that it would incinerate all of its contents (self-clean ovens). However, they would not use a conventional oven on Pesach.
Nonetheless, according to the letter of the law, Maran Rabbeinu Ovadia Yosef zt”l rules that there is a way to kosher a regular oven for Pesach. Indeed, his son, the great Rishon Le’Zion, Hagaon Rabbeinu Yitzchak Yosef Shlit”a, discusses this issue as well (Yalkut Yosef, Volume 3, page 360) and rules, as follows:
“An electric oven should be cleaned as thoroughly as possible and left unused for twenty-four hours prior to being koshered. It should then be turned on to its highest temperature and left on for approximately twenty-minutes so that the heat of the oven can remove the remaining vapors and steam that remain in the oven.”
In this manner, it will be permissible to use even a regular household oven on Pesach according to Maran Rabbeinu Ovadia Yosef zt”l. (Nevertheless, the oven trays where Chametz is baked within all year must be koshered through actual Libun. It is customary to use special trays for Pesach or disposable ones. Some act leniently and merely perform Hag’ala on such trays.)