Let’s continue the halachot (laws) of Chazara, to return on Shabbat on a hot surface. We use technical terms that we learned already in the previous days, but very quickly. The term garuf ve-katum is the action of removing the coals back in the days, or covering the coals. And you had the expression mechzi k'mevashel, which means that you’re using a device that is a normal way how to cook. So these two elements are what we’re going to use to understand everything.
There are three different levels when it comes to Chazara. If you have no garuf ve-katum, you have a live fire, so you cannot return anything, ever. If you have a live fire and a regular pot, and you’re in an Airbnb—you don’t have a platter, you have nothing—there’s a way to do shehiya (leaving food on heat) before Shabbat: put it on the fire before Shabbat starts. But returning it to the fire on Shabbat is impossible. Even if it’s fully cooked, even if it’s whatever you want, you can’t return it on the live fire. You cannot return it inside an oven. This is called mechzi k'mevashel. Even if it’s fully cooked, it’s mechzi k'mevashel, and it’s not garuf ve-katum; there’s nothing you can do.
Now, the other extreme case is the following: it is garuf ve-katum, and it is not mechzi k'mevashel. Take a platter, for example. It’s garuf ve-katum because the fire is completely, completely covered, and it’s not the derech (customary way) to cook on a platter. You don’t go on a Tuesday to cook dinner and say, “Yay, I’m going to use my platter.” No. We don’t use a platter for that. The platter was invented for Shabbat. I mean, it was invented for not cooking, for reheating something in a very slow way. That’s what the platter is. So it’s not mechzi k'mevashel. Somebody doesn’t say, “Oh, this person is cooking.” And it’s garuf ve-katum.
In this case, you could return something on the platter even on Shabbat, but only things that are not bishul, things that are not going to be a problem of cooking. So it has to be fully cooked, for example, and it has to be dry. If it’s not fully cooked and dry, then you’re cooking, and you have food to cook. So there are three sugiyot (topics) here. You also have the problem of bishul. You can’t put a raw piece of meat on, because you say, “Oh, it’s not mechzi k'mevashel, it’s garuf ve-katum, so I could put a raw piece of meat.” Of course not. You still have a problem of bishul. So you have to satisfy that also. This is the platter: garuf ve-katum, and not mechzi k'mevashel. I’m allowed to return something that doesn’t have a problem of bishul on Shabbat.
And then you have the middle. The middle is garuf ve-katum, but it is mechzi k'mevashel. If it’s covered—you cover it—but it’s mechzi k'mevashel. Let’s say you come and say, “You know what? I’m going to cover the fire inside my oven.” Some people may say, “If you do that, maybe it’s fine.” But how do you return there? Why? Because it’s the oven. Inside the oven, it’s mechzi k'mevashel. You have to do something that looks like you’re cooking, and therefore there’s no way to return this. So the Shulchan Aruch says over there, the only way to return there would be if you’re still holding it in your hands and haven’t put it down, basically, or if you put it down on something—but not on the floor—and it’s still hot. Because don’t forget, if there’s juice, you go back to the problem of bishul. So that would be the middle.
But in our ovens, you can’t do that because our ovens are not garuf ve-katum. If they’re not garuf ve-katum, there’s nothing you could do. You’re not allowed to put it back on a live fire, and therefore, inside the oven, you cannot do it. Even if you hold it in your hand, you cannot put it back. Once you take it out of the oven, there’s nothing you can return inside that oven, including Shabbat mode, Yom Kippur mode, Olam Haba (the World to Come) mode, whatever, Yom Shtuyot (day of foolishness) mode. You cannot return anything inside the oven on Shabbat.