We are continuing in our introduction to hilchos bishul. Yesterday, we learned about the definitions of bishul being a shinui aichus (change in the quality of the item) or a shinui tzurah (change in the form of the item).
The Gemara discusses a case of a person hardening wood by heating it in a kiln. Hardening the wood allows it to be used for building, and the Gemara says one is chayav for doing so. However, it is not a shinui tzurah, and there is not a significant shinui in the aichus (other than removing the moisture), so it is hard to understand why it is chayav. Rashi and Rabbeinu Chananel explain that while the moisture is coming out of the wood, it actually softens the item before it eventually hardens it. Therefore, it parallels the process of bishul, in the sense that bishul generally softens something, and one is chayav. The Rambam presents this case as a toldah of bishul, since it shares the quality of softening with bishul.
Rashi, and later the Mishnah Berurah, understand that every case of bishul must have an element of softening to it in order for it to be chayav. The Rambam writes that the melacha of bishul includes softening something which is hard, or hardening something which is soft. The Chayei Adam quotes the Rambam at the beginning of the klal. The Mishnah Berurah points out that the reason a person is chayav when they harden something is because it becomes soft before it hardens. On the other hand, there are meforshim (Lechem Mishneh perek 9 halacha 6) who understand the Rambam that even without the item becoming soft before hardening, the fact it changes form is a sufficient shinui tzura, and one will be chayav due to the shinui tzura even without a shinui aichus.
If the shinui can be accomplished without heat, or without heat to the level of yad soledes bo, it is not considered the melacha of bishul. It may fall under the melacha of makeh bepatish.
“Hot” is defined as a temperature that people broadly consider hot. Chazal define this temperature as yad soledes bo, where the heat is such that a hand instinctively pulls away due to the heat. People consider that to be hot, as most people will tell you that they can keep their hands in a place which is warm and only pull away because it is too hot.
The exact temperature of yad soledes bo is hard to define. Most poskim give parameters of a minimum at which we are concerned for yad soledes bo, and a number at which we are confident that it is considered yad soledes bo. Since we are dealing over here with issurei deoraysa, we will need to be machmir in most cases.
Rav Moshe Feinstein, who we will follow for this halacha, writes that 120 is the lowest minimum for yad soledes bo, and suggests elsewhere that maybe even 110 is yad soledes bo. Seeing that human body temperature is 98.6, it may be strange to hear that 110 is already a safeik. However, one must realize that 98.6 is internal body temperature, and not the temperature of the skin surface, while yad soledes bo is based on the reaction of the skin surface. (At the same time, body temperature is traditionally taken inside one’s mouth for this reason. Digital thermometers take temperature differently.) Rav Shlomo Zalman Auerbach writes 113 degrees would be the minimum for yad soledes bo.
As an upper number, Rav Moshe writes that 160 or 170 is a number which would certainly be considered yad soledes bo. We will clarify this point further in the upcoming shiur, be’ezras Hashem.
Summary
Bishul is defined as creating irreversible change in an item using heat (shinui aichus), or creating a reversible change which is of significance (shinui tzura).
If the shinui can be accomplished without heat, it will not fall under bishul, but may fall under the issur of makeh bepatish.
“Heat” is defined as yad soledes bo, the point at which one instinctively pulls their hand away. The precise number is uncertain. Rav Moshe Feinstein writes that 110 is already a safeik, and 160 is certainly yad soledes bo.
