Bishul is the melakha that prepares or improves food, whether through seething, baking, or roasting. What defines this melakha is that food is prepared by means of fire’s heat. The food is softened by the heat, and the tastes within it merge to create a new taste, which is intense and contains a variety of flavors.
Cooking initially softens food, and most foods remain soft after being cooked. However, there are some foods that harden in the course of cooking, like eggs. Similarly, the process of roasting softens the food at first, but eventually makes it tougher.
Torah law prohibits cooking, and this prohibition even includes foods that can be eaten raw, if cooking improves them in some way. For example, although one can certainly drink cold water, nevertheless, since cooking improves the water, doing so is prohibited by Torah law. Cooking foods that are not improved by this process is not prohibited by Torah law, but it is still prohibited rabbinically (MT 9:3; SHT 318:114).
One who cooks using fire or something that was heated by fire (toldot ha-esh) transgresses a Torah prohibition. Therefore, if one heats a frying pan on the fire, then turns off the fire and fries an egg in the hot frying pan, he has transgressed a Torah prohibition. This is the case even though the pan was no longer on the fire during the actual frying (SA 318:3; MB ad loc. 17; concerning cooking in the sun, see section 25 below).
Any accepted form of cooking is prohibited by Torah law. Therefore, one who cooks in a microwave transgresses a Torah prohibition, because nowadays this is one of the normal ways of cooking (Igrot Moshe, OĤ 3:52).
Before we explain the laws of Bishul in detail, we will preface them by saying that there are three types of prohibitions relevant to Bishul:
1. Bishul by Torah law;
2. Rabbinic enactments that forbid doing anything that might cause someone to turn up a flame (laĥatot ba-geĥalim, literally, “to stir the coals”);
3. Rabbinic enactments that forbid doing anything that resembles cooking.
To determine whether one may do a particular action, he must examine it from these three perspectives. To elaborate:
1. One must clarify if this action is forbidden because it qualifies as Bishul. Any action that leads to food’s transformation from a raw state to a cooked state is prohibited by Torah law. (This prohibition and those deriving from it will be explained in sections 3-13 below.)
2. From the perspective of the Torah prohibition of Bishul, one may leave food on the fire when Shabbat begins, with the intention that it will continue cooking on Shabbat. However, the Sages prohibit doing so when it may be necessary to adjust the heat, due to the concern that one may forget it is Shabbat and turn up the flame, thus transgressing the Torah prohibitions of Mav’ir and Bishul. But if the fire is covered, as it is in the case of a plata (warming tray), one may place food on it, because there is no chance that he will forget it is Shabbat and turn up the flame.
3. Even if a food is fully cooked, and thus there is no concern that one will turn up the flame, the Sages still forbid doing anything that looks like cooking. Therefore, one may not put fully-cooked cold food directly on the fire. However, one may put such food far from the heat source, in such a way that it does not look like cooking. (As we will explain in sections 18-21, there is disagreement whether placing food on a plata looks like cooking and is thus forbidden.)
4. A fundamental rule of the laws of Shabbat is that one may not create a new entity. During the other six days of the week, we emulate God, in whose image we were created, by busying ourselves with creating and developing. We take the raw materials of the world and develop and improve them, thus continuing the work of creation. Just as the Creator ceased creating on Shabbat, so too, we are commanded to emulate God’s attributes by establishing Shabbat as a day of holiness and rest. It is a day when we desist from creating new things, and thus enable ourselves to contemplate the world as God created it and increase our faith.
5. This principle is the principle behind Bishul as well. Cooking is forbidden because it changes a food from raw to cooked, thus giving it a new identity. But if the food is already cooked, there is no prohibition of reheating it, as reheating does not create a fundamentally new substance. Even when the reheating improves the taste, it is still not prohibited, following the accepted principle: ein bishul aĥar bishul (there is no prohibition of cooking something that has already been cooked). Therefore, the following question is critical to the laws of Bishul: When is a food deemed cooked? If it is considered cooked, then one may reheat it on Shabbat, and if it is not considered cooked, one may not do so.
6. Some of the greatest Rishonim disagree on this question. Some maintain that if the food can be eaten in a pinch, Bishul no longer pertains to it. However, in practice, it is agreed that a food is considered cooked only when it is fully cooked, and one could serve it to guests without feeling compelled to apologize. Before that point, even if one could technically eat it in a pinch, it is not considered cooked (SA 318:4). Therefore, in practice, it is important to determine whether a food is mevushal kol tzorkho (fully cooked). As long as it is not mevushal kol tzorkho, any action undertaken to raise its temperature and speed up the cooking process is prohibited by Torah law.
7. For example, the heat of a plata is often uneven; there are hotter and cooler places on its surface. One may not move a food that is not yet fully cooked from its current place to a hotter place on the plata. Similarly, one may not put a towel over the food to contain the plata’s heat more effectively. Furthermore, if one removes the cover of a pot in order to check if the food is fully cooked, and it becomes clear that it is not, it is now forbidden to replace the cover, because doing so will make the food cook faster.
8. However, if the food is fully cooked, one may move it to a hotter place, and if he took off the cover, he may replace it. Furthermore, one may cover the pot with a towel to preserve its heat. One may do so even if it improves the food’s taste, as it does with cholent. Similarly, one may remove fully cooked meat from the freezer and heat it (in a way that does not resemble cooking; see section 18). For it is an accepted principle that after a food is classified as cooked, it is no longer prohibited to reheat it. (All of this refers to solid foods; liquids involve additional issues that we will expand upon in sections 5-6.)
9. Cholent is considered fully cooked even if the bones in it are not soft, and one may cover it to preserve its heat. However, if one is accustomed to eating the bones, then as long as they are not yet cooked the food is not deemed fully cooked, and one may not cover it and preserve the heat.
10. A fundamental issue in the laws of Shabbat is establishing the temperature of yad soledet bo (the temperature at which the hand recoils). The Sages state that this is the minimum temperature that is still capable of cooking food. However, it is uncertain precisely what this term refers to. Does it refer to a level of heat that the hand can only stand to touch for a few seconds? If so, this would be approximately 71° Celsius. Alternatively, does it refer to a level of heat that becomes unpleasant for one’s hand after a few minutes? If so, this would be approximately 45°C.
11. According to many poskim, since the matter remains in doubt, one must be stringent. Heat of 45°C must be considered capable of cooking. Thus, one may not put raw food into a pot that has reached a temperature of 45°C or higher. Similarly, one may not place raw food near enough to a fire that it could reach 45°C or higher (SSK 1:1).
12. This definition is also important for how the laws of Bishul apply to water. One may not raise the temperature of water from below yad soledet bo to yad soledet bo or higher. However, if the water has already reached yad soledet bo, it is considered cooked, and one may continue to heat it further, because of ein bishul aĥar bishul. Cold water may be left near the plata as long as the water is in a place where it would not reach yad soledet bo even if it remained there for an entire day.
13. Thus, in practice, one must be careful not to heat water to between 45°C and 71°C; since we do not know the precise temperature of yad soledet bo, any heating in that range may be considered Bishul. But one may heat outside of this range. For example, if water has been heated to 71°C, one may then put the water in a place where it will get hotter, because of ein bishul aĥar bishul. Similarly, one may put cold water in a place where it will heat up, as long as the water does not exceed 44°C, because this kind of heating does not qualify as Bishul.
14. There is another important position that defines yad soledet bo. This position maintains that food or drink that most people would be able to consume all at once cannot be considered yad soledet bo. However, if most people would be unable to eat or drink it all at once, that is a sign that it is yad soledet bo. Thus, it would be considered cooked, and one may heat it further (Ben Ish Ĥai, Year 2, Bo 5; Maharsham 1:187; Yabi’a Omer 3:24, 4-6). In a case of necessity, one may rely on this position.
15. To create a safeguard, the Sages prohibited leaving water in a place where it could potentially reach yad soledet bo, even if one is standing there watching and waiting to remove the water before it reaches that point. They were concerned that the person watching might get distracted and forget to remove the water before it reaches yad soledet bo, thus making him guilty of cooking on Shabbat. However, if there is no possibility that the water will reach yad soledet bo even if it remains there for an extended period of time, one may place the water there (SA 318:14).
16. We have already learned that there is no prohibition of cooking something that has already been cooked. Therefore, one may reheat cooked food on Shabbat. For example, one may remove cooked fish or fried schnitzel from the refrigerator and reheat them to yad soledet bo, as long as it does not resemble cooking (see section 18).
17. But there is a fundamental disagreement among the Rishonim whether this principle applies to liquids like soups and sauces. For this purpose, a liquid is something that, if left in a bowl, would spread out evenly. If it retains its shape, it is considered a solid. According to Rambam, Rashba, and Ran, the principle of ein bishul aĥar bishul applies to cooked soup as well. Therefore, based on their opinion, one may take soup from the refrigerator on Shabbat and heat it, as long as it does not look like he is cooking (section 18 below).
18. However, according to Rashi, Rosh, Smag, and Smak, the principle of ein bishul aĥar bishul applies only to solid food, and one may reheat them on Shabbat. Liquids, on the other hand, even if they had been fully cooked, may not be reheated once they have cooled off, and doing so is considered Bishul. This is because when it comes to solid foods, the primary purpose of cooking them is to create the cooked or baked taste. Once bread is baked, the difference between eating it hot or cold is insignificant. The same is true of fish and potatoes; it makes little difference whether they are served hot or cold. Therefore, from the moment that these foods acquire a cooked or baked taste, their cooking is considered complete. Accordingly, even if they have cooled off, one may reheat them, because cooking no longer affects them significantly. But for liquids, their temperature is an integral part of defining them as cooked. There is a fundamental difference between cold soup and hot soup, and the same is true of tea and coffee as well. Therefore, for liquids, we say yesh bishul aĥar bishul (there is a prohibition of cooking something that has already been cooked). Thus, if a liquid has cooled down, one who reheats it to yad soledet bo transgresses the Torah prohibition of cooking.
19. Shulĥan Arukh rules in accordance with the stringent opinion (318:4), and Sephardim follow this ruling. Thus, for Sephardim, if a cooked liquid has cooled down to below yad soledet bo, it is no longer considered cooked, and it is prohibited by Torah law to reheat it past yad soledet bo. Therefore, Sephardim may not take soup out of the refrigerator and heat it. Similarly, if they remove soup from the plata, and it cools off to below yad soledet bo, they may not replace it on the plata. If it is known with certainty that the liquid is still yad soledet bo, it may be replaced (as long as it meets the conditions explained below in section 19). If one had situated it near the edge of the plata (which tends to be cooler), he may move it to the center and thus heat it more effectively.
20. If most of the food in a cold pot is solid, but the pot also has liquid sauce or gravy, one may not heat the pot. This is because by doing so one will also be heating up the liquid, which would constitute Bishul. The way around this is to remove the solid food and heat it by itself. One does not need to worry about the little moisture remaining upon it. Similarly, one may reheat cold food like meat or fish, even if there is a bit of wetness on them, because that liquid is not important and is batel (rendered insignificant) with respect to the solid food.
21. If food is congealed but will liquefy when reheated, like mushroom gravy, it is considered a solid food, and one may heat it (MB 318:100; Kaf Ha-ĥayim §158). However, according to Ashkenazic practice, le-khatĥila one should not heat it because some maintain that le-khatĥila one should not take an action that will cause food to change from liquid to solid or the reverse, because this is like producing something new (see 12:12 below). However, if the gravy is secondary to the solid food, then even Ashkenazic custom would permit le-khatĥila heating the food together with the congealed sauce or gravy, which will liquefy.
22. As we have seen, according to Rambam, Rosh, and Ran the principle of ein bishul aĥar bishul applies to liquids as well as solids. Thus, as long as the liquids were fully cooked, even if they have now cooled off, one may reheat them to yad soledet bo.
23. There are many Yemenite Jews who consistently follow Rambam’s rulings throughout halakha. Therefore, if they serve soup Friday night and then put it in the refrigerator, they may remove the soup from the refrigerator on Shabbat day and reheat it. This is the law for sauces and all other liquids as well.
24. Ashkenazim follow Rema, whose opinion is a kind of compromise between the previous two. If a liquid has cooled off to the point that one normally would therefore not consume it, then one may not reheat it to yad soledet bo. But if it is still warm, one may reheat it to yad soledet bo. This is because Rema fundamentally accepts the position of Rambam that ein bishul aĥar bishul applies to liquids as well. However, in his opinion, if a liquid has cooled down entirely, it is rabbinically forbidden to reheat it.
25. When one who follows the position of Shulĥan Arukh or Rema is a guest at the home of a Yemenite who follows Rambam, he may eat soup that his host heated on Shabbat. Since the host is following halakha based on the accepted practice of his community, any Jew may eat his food le-khatĥila (see MB 318:2.).
26. However, one who follows the Shulĥan Arukh or Rema may not ask one who follows Rambam to heat soup for him. Since his own community forbids reheating soup, he may not ask his friend to do it for him. But if he invites his friend to eat with him, his friend may follow his own custom and heat soup for himself. In such a case, the host may eat from it as well.
