Earlier we learned about Bishul, which is prohibited by Torah law. Now we will examine two rabbinic enactments:
1) On Friday afternoon, one may not leave on the fire foods that are not yet cooked.
2) On Shabbat, one may not do things that resemble cooking.
We will begin by detailing the first enactment.
As a rule, the prohibitions relating to Shabbat begin when Shabbat begins. Therefore, by Torah law one may put a pot on the fire before Shabbat even though it will continue to cook on Shabbat. But the Sages were worried that one would be so anxious for his food to be properly cooked by Friday night that he would turn up the flame on Shabbat, thus transgressing the prohibitions of Mav’ir and Bishul. The Sages went even further and decreed that if one’s food needed more time to cook and he decided to leave it on the open fire, it may not be eaten on Shabbat.
In the past, cooking was done in a kira, a mini-oven that was heated by burning coals on its floor. The Sages were concerned that one would stoke the coals to accelerate the cooking process. Today, since we cook on gas flames, electric burners, or ovens, the equivalent concern is that someone will turn up the flame or raise the temperature, thus similarly transgressing the prohibitions of Mav’ir and Bishul.
Even if one were to leave the burners or oven on their highest temperature, rendering it impossible to turn up the fire, this is still forbidden; the Sages did not differentiate in this enactment. Furthermore, one might turn down the flame and raise it again later. Additionally, anytime one leaves uncooked food on an open fire, there is a concern that he will transgress Bishul in some way, such as by stirring the food or by covering it to preserve the heat.
There are two situations where there is no concern that one will raise the temperature, and, therefore, one may leave the food on the open fire or in the oven:
1) When the food is ready to eat, it can be left on the fire because there is no reason for anyone to raise the heat.
2) If the food is not yet fully cooked, it can be left on the fire if the fire is contained. In the time of the Sages, this meant that the coals had been cleared out of the oven (garuf) or covered with ash (katum) to lessen their heat. Today we accomplish this by covering the flame, which is why a plata may be used in this situation – its “flame” is naturally covered. In the upcoming sections we will continue explaining these two permitted cases.