We are beginning siman 1. The Chayei Adam divides his sefer by klalim and simanim, rather than the traditional simanim and seifim.
The Chayei Adam writes that one who bakes bread or cooks food or samimanim (inedible dyes) transgresses the melacha of bishul.
The Chayei Adam stresses samimanim to include cooking inedible items. One may mistakenly think that bishul only applies to food, but it cannot be true, since we learn the issur of bishul from the dyes which were cooked in the Mishkan.
The Chayei Adam writes that heating water is also bishul.
The Chayei Adam stresses water because water does not get significantly changed by the cooking process (besides for organisms not visible to the naked eye). Nevertheless, it is still under the issur of bishul, because adding heat to the water is a significant enough shinui that people use hot water very differently than they use cold water.
The issur of bishul applies to items which are edible raw, including milk and fruits. Even though there may not be a shinui aichus when these items are cooked, it is still a significant enough shinui in the way people consume them to be considered bishul. This is also true about milk, even though the shinui is reversible once the milk cools down. There are some poskim who argue that heating milk kills the various bacteria in it, which creates an irreversible change and is an even stronger reason to be chayav.
The Chayei Adam continues, and writes that melting wax, tallow (rendered fat from an animal for fuel), tar or other similar items is chayav.
Heating metal to the point that it softens will be chayav as well. They would put metal into a crucible, heat the crucible to the point that the metal melts, and then pour it into a mold. The change from solid to liquid also falls under the melacha of bishul.
Similarly, baking clay in a kiln creates a significant change in the clay, and it is chayav.
Finally, drying out wood in the oven in order to remove the moisture from the wood is chayav.
Summary
The issur of bishul includes food and non-food items, and applies when the item is significantly changed through heat.
