Washing a hot pan in cold water can cause it to warp says Chris Tracy, manager of Calphalon culinary relations. “The bottom of the pan will become uneven, and the pan will not sit on the burner securely.” This can be a safety issue if the pan spills or falls off the stove, and foods may not lie flat in the pan during cooking.
Why? “When any metal gets hot, it expands on the molecular level,” explains Mark Kelly, the marketing promotions manager at Lodge Cast Iron Cookware. “If the metal cools off too quickly, the molecules constrict too quickly, warping [the pan].” This is called thermal shock.
The bigger the difference in temperature between the liquid and the pan, the more intense the shock, says Tracy. So, for instance, if you deglaze a pan with tepid or room-temperature wine, that’s fine he says. But “if the liquids are cold or chilled, then they have a higher probability of causing thermal shock.”
Tracy says that warping is a concern for all types of metal, but that generally, the thicker the pan, the more resistant it will be. When it comes to washing, he suggests letting pans cool briefly and then putting tepid water on them. Also, he cautions that “you should always avoid complete submersion until the pan has cooled.”