Stump the Scientist question submitted by reader Carol:
I love to cook and bake but have been having a problem for years trying to get a specific fudge recipe to work. I cannot get the ingredients to reach a high enough temperature when stirring them in a pot on my stove top. Is there any scientific way to get the ingredients to get any hotter? Do I need to buy a pot made from a certain ingredient? I just thought there might be a scientific way to explain what I am doing wrong!
Response from Chief Scientist Jim Bray:
While I claim no talents as a chef, there is at least one scientific principle at work here. This principle is utilized in pressure cookers for cooks.
A liquid can only be heated to the temperature at which it boils in a normal room atmosphere. When it gets to this boiling temperature, any attempt to make it hotter will only make it boil more furiously, and its actual temperature will not rise further. For example, the boiling temperature for pure water is 212 F (100 C). To increase this temperature, it is necessary to increase the atmospheric pressure above the boiling liquid. That is what pressure cookers do. By providing a pressurized environment, the actual cooking temperature increases, and the time for cooking generally decreases. The amount of temperature increase depends on the amount of increased pressure, and that depends on the safety of the containers provided by the manufacturer.
If the liquid has not yet reached boiling, then it can be made hotter by increasing the heating source (gas or electric) on the stove.