Heating a pan prevents food from sticking by closing cracks in the metal
March 31, 2011
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Most cooks know that you should start with a hot pan to prevent or minimize food sticking. You may hear a bizarre theory that goes something like this: food sticks to pans because it seeps into minute cracks and pits in the pan and then solidifies when heated, becoming stuck. If you heat the pan before adding the food, the metal expands and fills in the microscopic cracks and holes in the pan’s surface or at least makes them smaller. With fewer or smaller surface defects for the food to grab onto it is less likely to stick.
Unfortunately whoever came up with this idea knew nothing about the physical properties of metals. When metal expands due to heating, each individual atom vibrates faster and faster and thus takes up more space. The result is the same as if each atom simply got a bit bigger, and the result is that the entire piece of metal, defects, holes and all, gets bigger. Thus, if you heat a donut-shaped piece of metal, the outer diameter gets bigger and so does the diameter of the hole. You have probably used this fact yourself when trying to get a metal screw lid off a glass jar. Running hot water over the lid expands the entire lid and loosens its grip on the jar, making it easier to remove. So, heating a pan would cause these hypothetical surface cracks to get larger, not smaller.