I found an interesting bit of info on the science of caramelization which as we all know is the reduction and stages of water and sugar into caramel or caramelization. I still have not found any convincing data that suggests the temp of the bottom of the kettle to be much above 212F if any at all. Although I have a sneaking suspicion the bottom surface is slightly above 212F.
The following info was taken from this link.
http://en.wikibooks.org/wiki/Cookbook:CaramelThe Science of Caramel
Essentially, caramel is melted sugar. As sugar increases in temperature, it reacts in a process similar to burning that results in the creation of a wide variety of complex molecules. These molecules provide the deep, rich flavors and colors that make caramel so special.
There are two basic ways to make caramel: the dry method and the wet method. The dry method, which involves slowly heating sugar until it melts, is more difficult. The more commonly used wet method is easier and does not require any special tools.
In the wet method, granulated sugar is dissolved in water, then boiled until the water starts to evaporate. As the water escapes, the solution passes through a series of stages that indicates the ratio of water and sugar. This ratio is directly proportionate to the temperature so if you understand the stages, you do not need a candy thermometer. Nevertheless, use of a thermometer minimizes the handling of the (very) hot mixture.
The stages of a sugar solution are generally described by the solution's behavior when dropped into cold water:
Thread Stage (230°F) - the solution thickens into syrupy threads when you pull a spoon out.
Soft Ball Stage (234°F) - the solution can be pressed into a soft gooey ball. Used to make soft chewy candies like taffy.
Hard Ball Stage (250°F) - the solution can be pressed into a dense, slightly malleable ball. Used to make harder chewy candies.
Soft Crack Stage (270°F) - the solution solidifies into a glass-like solid that slowly bends under light pressure.
Hard Crack Stage (300°F) - the solution solidifies into a hard glass-like solid that breaks or cracks under pressure. Used to make hard candies and brittles.
Caramel Stage (310°F) - An advanced crack stage, defined by the development of an amber color that becomes tan, brown and eventually dark brown as the temperature continues to rise. Also defined by the development of caramel flavors which becomes deeper, less sweet and more bitter as it darkens.
Burned Stage (350°F) - The sugar is completely oxidized (burned) and turns black. It is inedible.
