Returning Food to an Oven on Shabbat | Rabbi Daniel Mann | Beit Midrash

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Question: My electric stove has a Shabbat mode, which enables us to cancel the automatic shut off (needed for 2 days of Yom Tov) and keeps the exact heat you set without fluctuation when the door is opened. On Shabbat, can fully cooked dry food be placed in the oven to be warmed up?

Answer: We will try to make a little order in what the Shabbat mode does and what it does not do. We will be able to provide only an overview of the most basic of the many complex halachot that remain to be discussed.
The main element of the type of Shabbat mode you describe is to circumvent systems in modern ovens that cause problems for Shabbat. The obviation of the shut-off feature is of technical value for the Shabbat observer and is irrelevant to the question of returning food on Shabbat.
Another element is to circumvent the direct impact of opening the doors on a variety of lights, sensors, etc., which would make opening the door forbidden. Regarding an oven in which even in Shabbat mode it works with a set temperature that is controlled by a thermostat, there is still an issue that opening the door cools off the chamber and causes the oven to turn back on sooner and/or stay on longer, which is debated by the last generation’s poskim (see Shemirat Shabbat K’Hilchhata 1:29 – stringent; Igrot Moshe, Orach Chayim IV:74.28 – lenient; Yalkut Yosef, OC 253:5 – inconclusive). There are ovens in Israel with Shabbat modes that cause the oven to work steadily at a low intensity without a thermostat, and it is thus not a problem to open the door. That does not appear to be the system you are describing.
In any case your question relates to the rules of hachzara (returning food to a heat source), which is a stricter application of the laws of shehiya (having the food stay on the heat source). The basic law of shehiya is that one may not leave food on a heat source on Shabbat when he may have an interest to raise the heat and an ability to do so, without certain steps to reduce that concern. A blech, for example, works by reducing the intensity of the heat on the food by covering the flame, and thus serving as a reminder that reinforces the message not to consider increasing the heat. Non-adjustable hot plates make it unfeasible to raise the heat and thus are permitted. An oven is problematic in that it is hard to duplicate the positive these elements and its heat is adjustable. Leniency can be contemplated if one tapes up the controls or based on the Rama’s (OC 253:1) minhag that for foods that are nominally cooked, there is little interest in raising the heat.
Returning dry food to an oven on Shabbat is much more problematic (including, that it might look like cooking), and it apparently requires the fulfillment of six conditions (see Shulchan Aruch, OC 253:2): 1) The food must be fully cooked (easy); 2) The heat source must be covered according to the aforementioned criteria (see above); 3) If one takes food off, he must hold it if he wants to return it (not feasible in your case); 4) One has to have in mind, when removing the food, to return it to the heat (easy); 5) The food did not cool down (not feasible). 6) The food should be put onto an open heat source, not into an enclosed one, especially when it is a place where food is often cooked (see Mishna Berura 253:58; Yalkut Yosef OC 253:8). An exception to these requirements is a place that is less hot than yad soledet bo (app. 45̊ C= 113̊ F) (Rama, OC 253:2) or one made for reheating rather than cooking where it is also not feasible to adjust the heat. These include ovens that are off with residual heat (Rama 253:5) and, according to some, non-adjustable hot plates made for Shabbat reheating (see Yechaveh Da’at II:55).
There are certain conditions in which there are opinions (including one by Rav Soloveitchik, which requires much explanation) that one can reheat in an oven, and you are free to ask the rabbi of your choice about the matter. The point of this overview is to explain that your Shabbat mode is no better in regard to reheating than standard ovens of decades past.