9. Many homes have only one oven, often fleishigs. During the days leading up to Shavuos, women want to bake milchige dishes in their ovens and many people ask how and when it is possible to do this.
10. The accepted and best way to do this is by cleaning the oven, waiting 24 hours from the last time it was used for fleishigs, and then performing libun kal by running it on its maximum heat setting for a certain amount of time, as will be explained.
Cleaning the Oven
11. First, the oven must be cleaned thoroughly with a strong cleansing agent until there is no food matter on its walls, floor, or pans. Stubborn spots of old, burnt food on the walls that do not come off after a thorough cleaning do not need to be removed, since they do not have intact food matter and do not give off steam or an aroma. Also, the poskim hold even libun kal burns off any leftover substance (פמ"ג ); at the very least, the cleansing agent certainly ruined any flavor.
Waiting 24 Hours
12. Before baking milchigs, one should lechatchiloh wait 24 hours from the last time the oven was used for fleishigs, even if he is going to run the oven on its highest setting. This is because even though we hold running the oven on its maximum heat setting accomplishes libun kal, in some ways it may not be a true libun kal. Thus, if possible, it is proper to also wait 24 hours so that the oven is not a ben yomo when it is used for milchigs.
13. Used in between for parve. Even if the oven was used for parve within 24 hours of its last use for fleishigs, the 24-hour waiting period does not need to be restarted; it always starts from the last time it was used for fleishigs.
14. Pressing situation, cannot wait 24 hours. If one is in a pressing situation and cannot wait 24 hours, he may be meikel and kasher the oven without waiting, since some say waiting 24 hours is only necessary for hagoloh, not libun.
Libun Kal
15. After cleaning the oven and waiting 24 hours, the oven should be run on its maximum setting for one hour in order to kasher it. Then, it may be used even for uncovered milchige food.
