As we explained, utensils must be koshered in the same manner they absorb the prohibited substance, for instance, a pot that Chametz soup was cooked in is koshered through Hagala, i.e., placing it in a bigger pot containing boiling water. This purges the pot of the Chametz flavor that was absorbed in it.
A Pressure Cooker
It is therefore sufficient to purge a pressure cooker in a large pot containing boiling water. Although the temperature within a pressure cooker can reach over 250 degrees Fahrenheit during cooking, which is greater than the heat of the boiling Hagala water which only reaches approximately 212 degrees, nevertheless, this difference in temperature does not affect the laws of koshering and only the method of Chametz absorption is important to us. Thus, anything which absorbs liquid on the fire, such as a pot, can be koshered through Hagala in boiling water on the fire. Something which absorbed only by means of a “Keli Sheni,” such as a metal bowl where boiling Chametz is poured into from a pot on the fire, can be koshered by pouring boiling water from a “Keli Rishon” (such as an electric kettle) onto it. The above applies even to a pan used to fry Chametz falafel, for although the oil in the pan can reach temperatures of approximately 375 degrees, Hagala in boiling water is sufficient to kosher this pan.
Nevertheless, loaf pans or cake pans (molds used to bake breads or cakes) cannot be koshered through Hagala, for they absorb the flavor of dry Chametz, and they must be koshered using a method called “Libbun” or torching. Nowadays, there are specific places in religious neighborhoods where Libbun and Hagala are performed in a professional manner using gas burners and blowtorches.
Stoneware shares the same law as metal vessels and can be koshered using the same method in which it absorbed the Chametz. Thus, just as loaf and cake pans can only be koshered through torching with fire, so too, a chamotte (pizza) stone must be koshered in the same manner. However, since this pizza stone cannot endure such high temperatures, in addition to the fact that some claim that since it is not a natural stone, it is comprised of some materials that cannot be koshered, this chamotte stone should not be koshered for Pesach.
Mixers (Kitchen Aid)
According to the letter of the law, one should have been able to kosher a mixer by taking apart all its various parts and cleaning them well. Nevertheless, since a mixer uses flour and this flour enters the various cracks and crevices of the machine, most great Poskim advise against using such a mixer on Pesach. Indeed, Hagaon Rabbeinu Yitzchak Yosef Shlit”a rules (in his Yalkut Yosef- Pesach, Chapter 451) that one should not use such a mixer on Pesach even after cleaning it well. It is preferable to buy a mixer specifically designated for Pesach use. (If one nevertheless wishes to kosher a mixer, there are some detailed laws for this; see Yalkut Yosef ibid page 421.)