As in many things, confusion comes in with stoves and ovens, as the ancient forms of these objects had little resemblance to what we use today. Rules stated about the ancient ovens may or may not be applicable to today's ovens.. The ancient oven was similar to what is called in Arabic a "tab'un"; a sort of drum shaped (wider at the bottom, narrower at the top) clay (or sometimes metal) device, heated from the outside, where bread was baked by simply slapping it on the inside wall, removing it when ready. Many Yemenites still make matzah this way. (I used to get it when I lived in Southern Israel, during my last three years there). Stoves were usually box like instruments, with one or more wholes on the top, in which pots would be placed. There was a fire burning inside, of differing intensities for different sizes of stoves. Later,in Eastern Europe, there was a common type of stove that was actually a room heater, powered by wood or coal,, but whose surface was also used for cooking. I have seen these still in use in Ukraine.Rabbis differ about our modern stoves and ovens. This has great implications for not only kashrut, but for laws of Passover and Shabbat as well. Some see an oven as essentially unkasherable. Its surface is often enamel, which is questionable. Its metal grates, used to hold the pots while cooking, are likewise seen by some as non kosher, as they often receive overflow of both meat and dairy pots. The oven racks are metal, but they cook without liquid, and would theoretically need "libun" (heating until the metal glows) to make them kosher. Therefore, many people use different grates for dairy and meat pots, or keep them covered with aluminum foil, especially for Passover. (When one walks into an Ashkenazi  kosher home today during Passover, the ubiquitous aluminum foil is blinding. I use none). Many use a blow torch on the oven, and then cover it anyway with metal inserts, since it will never turn white hot. Others, take a more middle ground approach. They will leave the oven unused for 24 hours between meat and dairy, as well as before Passover. Then, they will let it run at top heat for an hour or more. This would then be suitable for cooking in or on it, so long as food does not deliberately touch the stove or oven themselves. If a piece of food did happen to fall on it, after twenty four hours, the stove or oven will no longer be a problem, as we have seen. The kashering is a formality, lest we come to use them within twenty four hours. The metal grates upon which the pots rest during cooking, will either be heated in the oven or otherwise burnt, and would then be likewise permissible for indirect cooking (that is, in a pot or pan). This is the method most seen. Rabbi Ovadia Yosef permitted simply pouring boiling water on the grates. Rav Y. Abadi takes an entirely different route. He points out that our ovens run at a consistently high heat, unknown in ancient times. Any splatter of food is almost instantly burned. This is also true of the grates. No kashering necessary! For Passover, he recommends getting the oven to top heat, and leaving it there for half an hour. For stove tops, where food may fall inadvertently, they should be cleaned with soap and water, and we are good to go.This is the method that I follow in my home. The only area of care that I exercise, is not to leave both meat and dairy on the oven at the same time, as splatter from pot to pot is not uncommon.Cooking meat and dairy in the same oven at the same time is technically permissible, provided that one is covered. I avoid this as well, for fear of splatter. Next time, I will deal with a bit of a controversial topic that I mentioned in passing in my last post: the issue of foods that are not actually hot, but are very pungent. As you have probably guessed, this is a serious issue for Ashkenazim, and a very minor one for Sepharadim. Next time