Cooking, the av melachah of bishul,1 is forb idden on Shabbat. Although the word bishul means cooking, the melachah is better defined as enhancing a substance—food or non-food—by fire-generated heat. Enjoying hot food on Shabbat is a mitzvah, so it’s important to understand the complexities of bishul to ensure that Shabbat is celebrated correctly.

One transgresses the melachah of bishul by heating liquids or solids to the point that they have significantly improved and are fit to consume. For food, this means cooking to the point of ma’achal ben druso'i,2 which some authorities define as half cooked,3 others as one-third cooked.4 Liquids are considered cooked when they have reached the point of yad soledet bo - the point at which one’s hand would recoil because of the heat. The exact temperature of yad soledet bo is widely disputed, with some authorities putting it as low as 110 degrees Fahrenheit (43 degrees Celsius).5 Speeding up the cooking process by stirring food that is hot but not yet cooked also falls under the prohibition of bishul, as does covering a steaming pot of uncooked food.

Reheating liquids that have already been cooked and fully cooled down falls under the Biblical prohibition.6 Reheating cooked solid (dry) food, however, is permitted and is not considered bishul (see important caveats below). The reason for this distinction is that once a food is cooked it has already experienced a meaningful change. Heating it again doesn’t really add anything. Cooked liquids, on the other hand, are rarely consumed in their cold state and need to be heated to be enjoyed. Therefore, just heating them up enhances them greatly, making one liable for bishul. Solid food, in this regard, refers to food that has no moisture, like bread. If the food is even slightly moist on the outside, like sauce on chicken, reheating it on Shabbat is forbidden.7

Heating food, using a medium that was heated by fire, toladot aish, is also Biblically prohibited on Shabbat. For example, adding cold food or liquid into hot food or liquid, such as adding cold water to thin out a thick soup that was just taken off the fire. In this scenario, we don’t look at how hot the food is, but whether it is still in the same pot or pan in which it was cooked. Halachah considers the original receptacle to be the most problematic, since it has been on the fire and is more likely to retain heat and cause bishul. Putting bishul-susceptible food into a pot that was previously on the stove, with contents that are yad soledet bo, is a Biblical transgression. If the contents of the pot have been transferred into another container, called a kli sheni (second vessel), adding bishul-susceptible food is definitely a rabbinic prohibition, and may also be Biblical.8

Some authorities maintain that bishul can also be transgressed by cooking something after it was already baked or roasted or baking or roasting something after it was cooked. For example, adding roasted meat into a steaming pot of cholent.9

Rabbinic Prohibitions

There are many rabbinic prohibitions connected to bishul. Here, we will focus on quite a common one, which restricts performing shehiya - leaving food on the stove before Shabbat to finish cooking automatically on Shabbat.

Biblically, there is no issue with putting food on a stove before Shabbat and allowing it to continue cooking on Shabbat itself.10 The sages were concerned, however, that allowing one to do so might bring him or her to raise the heat on Shabbat to ensure that the food would be cooked in time, which breaches the melachah of mav’ir - burning, and can also involve bishul. Because one would only be tempted to speed up the cooking process if the dish still required a fair amount of cooking, the sages established a point at which a dish is considered sufficiently cooked that we needn’t worry one will want to adjust the heat.11 The sages ruled that one who wishes to put a dish that is not, at a minimum, ma’achal ben druso'i, on the stove, is required to turn off the fire12 or cover it. By doing so he demonstrates that he isn’t really interested in involving himself in the cooking process, so we aren’t concerned he will adjust the heat of the fire. The way this is commonly done is to put a thin sheet of metal called a blech over the fire, and the food is placed on top of it. Some authorities also require one to cover the knobs of the stove. Although this method is fully permissible halachically, to avoid any issues that may arise, the authorities exhort one to try to have all food fully cooked before Shabbat, and put it on a blech simply to keep warm.13

Bishul in the Mishkan

Certain herbs and plants were cooked to produce dyes for the Mishkan.14 Additionally, the lechem hapanim (showbread) was baked each Friday to be put on display in the Mishkan on Shabbat.15

Common Activities to Avoid

  • Pouring hot water straight from an urn onto coffee granules or a teabag
  • Seasoning cholent while it is still hot, in the pot in which it was cooked
  • Taking the cover off a pot of cholent if it is not yet fully cooked