Blowing really does cool off your soup

Hot molecules are hopping around

Dear Mr. Alice: I was contemplating a hot bowl of soup the other day, eager to eat but reluctant to burn my tongue. So of course, I scooped up a spoonful, blew on it a few times, stuck it in my mouth, and swallowed. Does this silly ritual that we’ve all gone through a hundred times actually do anything to cool off the soup, coffee, whatever? Or is blowing on hot soup kind of like crossing your fingers for luck, an irresistible urge but ultimately ineffective? Does your cooler-than-soup breath lower the temperature? Or what? — Sharon, San Diego

Pucker up and blow, Sharon. It will work every time. Hot soup molecules are hopping around in the bowl. The hotter they are, the higher they rise, until they fly off the surface into a hovering vapor cloud. The soup cools slightly as the hottest molecules depart, but then the cooling stops when the microclimate over the bowl becomes saturated with vapor. Blow away the vapor, and the fresh air can take up a new round of hot molecules.

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