The question is asked in Halacha regarding our gas or electric ovens that we have in our homes. Is it permissible to use them for both milk and meat? If it is permissible then how are we supposed to use them?
Firstly, it should be said, that Lechatchila (the best and right way to fulfill the Mitzvah) if a person has the ability and the space, in order to avoid all problems, it would be best to have separate ovens for milk and meat.
But letís now talk about where you only have one oven.
Halacha writes that foods give off ĎZea.í Zea literally means a sweat or a type of vapor that comes out of the food when cooking it, when it gets heated. This vapor goes onto the walls of the oven. So therefore, we are concerned that when putting a dairy item into the oven right after a meat item, that the sweat from the meat item which vaporized which is now on the oven walls will now fall into the dairy item. That would of course then make the dairy item forbidden to eat.
There are many Poskim that hold that liquid foods specifically give off Zea as opposed to dry foods. A cake or a spaghetti or something like that which is put into the oven that is a dry food, according to many Poskim does not give off Zea. But something liquidy like a roast in gravy or something with juice, would give off Zea. So we have to see if there is a difference between dry foods or liquidy foods.
The Halacha, Chacham Ovadia is very Machmir when it comes to liquidy foods. He said the way you should use it, Lechatchila, is to cover the food when you put in the oven. For example, you take a piece of tin foil and cover it. Then you would be able to put milk after meat or meat after milk because it was covered. If it is not covered, you should wait 24 hours after cooking something that is liquid and, you then burn the oven for 15 minutes before you cook the next item. Bediavad (an acceptable, but not best way to fulfill a Mitzvah), Chacham Ovadia holds it would be OK even if you do it within 24 hours.
Similarly, by a dry item, Chacham Ovadia says, Lechatchila one should wait 24 hours, burn it out for 15 minutes, and then put the milk or meat to follow.
So again, when it comes to liquidy items, one should Lechatchila always cover them in the oven. If you didnít cover them, and Bediavad you didnít even wait 24 hours, there is what to rely on. But again, Lechatchila it should be covered if there is liquid. If there is no liquid then the rule is you should wait 24 hours in between. You burn out the oven for 15 minutes which is a normal thing anyway, whereby you heat up an oven before you put foods in. And then you would be allowed to use it.
Lemaíase, Chacham Rav Moshe Feinstein is a little more lenient than Chacham Ovadia on this. And he says on dry items, you donít even have to wait anything. Because there is no Zea at all. He holds that you can just cook meat and then take it out and put the milk in right away and you donít have to worry about anything. Especially it says, on the ovens that have the fire on the top. So he says the Zea is burnt immediately, which means there no Zea at all.
The Halacha, Chacham Ovadia is Machmir on this even by dry items. One should wait 24 hours before using the oven. And thatís again only talking if it only was revealed. If it was covered, then you donít have to worry about anything because the Zea can not go onto the ovens.
So Halacha Lemaíase, we are Machmir more by liquid than by dry items. Meaning that by liquids, Lechatchila, you should always have them covered. If it wasnít covered, one should wait 24 hours between milk and meat, and then burn out the oven for 15 minutes. Bediavad, even if he didnít wait 24 hours there is room to be lenient. By dry foods, Lechatchila, one who waits 24 hours he has no problem. Otherwise, Bediavad, if you did not wait anything, you have what to rely on, as we brought the Posek Rav Moshe Feinstein.