If food was left in the oven which is on to continue cooking on Shabbos, can I take out the food from the ON oven on Shabbos?
Ovens are challenging to use for Shabbos and Yom Tov, for a number of reasons. The main problem with using them on Shabbos is the thermostat, which is affected by opening or closing the oven. When the oven door is opened, the thermostat will detect the cold air that rushes in and will activate the heating element if it is off at that moment. It is forbidden to cause this to occur, even if all the food will be removed all at once before the oven door is re-closed. [If the oven door is re-closed with some of the food remaining inside, there may be additional concerns of Bishul on Shabbos, depending on the circumstances.]
Yet another problem, applicable on both Shabbos and Yom Tov, is that many models have lights or fans that are activated and deactivated as the door is opened or closed. In summary, a modern oven without Sabbath Mode may be completely unusable on Shabbos and Yom Tov.
The above answer focuses purely on using the oven itself. However, there are also restrictions about which foods may be placed in an oven before Shabbos without a Blech, and much discussion about whether, and how, a Blech can be facilitated in an oven.
Here is a brief summary of the issues:
From the Torah perspective, one may place food over an open flame before Shabbos in order that it cooks on Shabbos. Nevertheless, Chazal forbade this due to the concern that a person may come to stoke the fire on Shabbos in order to speed up the cooking process. This prohibition is known as Shehiya.
One method of avoiding Shehiya is to cover the flames, typically with a Blech. Covering the fire indicates that one does not desire a strong flame, it diverts his attention from the fire, and it serves as a reminder not to increase the flames. With regards to an oven, there is a dispute whether – and how – a Blech can be adequately created. In practice, a Blech in an oven should be situated so that it covers the heating elements, which may be located either at the top of the oven, the bottom or the back-wall. In many ovens, there are heating elements in all of these places.
Another way of addressing Shehiya, and to sidestep the need for a Blech, is to ensure that the food is cooked prior to Shabbos. It is sufficient if the food is already half cooked. This fraction does not represent time, but rather, is qualitative and measured against the degree of cooking most people would regard as fully cooked. Nevertheless, for a number of reasons, it is best that the food be fully baked before Shabbos.
There is yet a third possible way to circumvent the prohibition of Shehiya. Chazal allowed one to put completely raw meat on an open flame just before the onset of Shabbos. They were not concerned that one might come to stoke the flames, because doing so would not serve any productive purpose – it would not ready the meat in time for the Friday night meal, nor would it be necessary to ready the meat in time for the Shabbos day meal. This leniency is known as “Kidra Chaysa” – literally: raw pot. (Indeed, some people may wish to put raw chicken and rice right before Shabbos to slow bake in the oven for the daytime Seudas Shabbos.)
In order for this leniency to apply, two criteria must be met. First, the food item must be one that takes a relatively long time to cook properly (such as meat). Second, the food must be put on the fire just before Shabbos, late enough that it will not begin cooking before Shabbos comes in. Some contemporary Poskim therefore assert that this leniency seldom applies nowadays, because most modern cooking appliances are able to cook in a relatively short amount of time. As a case in point, meat put up to cook right at the onset of Shabbos would usually be fit for consumption by the time the meat course arrives. Even if the heat is set to low, this does not diminish the oven’s overall ability to bake quickly, because the seat heating can be easily raised. Thus, according to these Poskim, this option is not applicable to a modern oven.
Other associated issues:
1. It should be pointed out that even when the oven is off and cold, if it will be turned on with a Shabbos clock or a timer (see next point), one may not place inside any food which is not completely cooked. Furthermore, even completely cooked food that has cooled down may not be placed inside either, unless the food is completely dry (and will remain dry when heated). The same applies to an oven which will remain off but has not yet cooled down.
2. With regards to Shabbos clocks in general, the Rebbe writes in a letter (Igros Kodesh Vol 12 page 192): “There are those who are extremely stringent and are even skeptical about the permissibility of using a Shabbos clock… Therefore, I am abstaining from giving this idea in an official capacity.” Even so, it is reported that the Rebbe instructed some individuals that they may be used (See Shulchan Menachem Volume 2 page 173). At the same time, many authorities who permit Shabbos clocks in general nevertheless rule that they should not be used with regards to cooking specifically, for a number of reasons.
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