We’ve all been told to blow on a hot drink or bowl of soup before sipping from them, in order to help cool it down a bit so we don’t burn our tongues and mouths. Most of us practically do this on instinct, without even thinking about it.
While this age-old trick may seem like another old wives’ tale, it turns out there’s actually some science to back this one up. It’s not going to completely cool down a hot beverage or soup, of course, but it will reduce some of the heat.
Basically, no matter how warm your breath is, it’s not going to be as warm as a piping hot cup of coffee or tea. Thanks to heat conduction, the air molecules from your breath and the molecules of the steam want to be as close to the same temperature as possible so they’ll exchange heat. So some of the heat from your tea, coffee, or soup will transfer to the air, cooling it a bit.
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Additionally, blowing on hot, moist air to replace it with some cooler, drier air will makes the evaporation process speed up, and evaporation causes your coffee or tea or hot chocolate’s temperature to drop a bit as well. Stirring it will encourage quicker evaporation too.
So keep blowing on your hot drinks and soups– you’re actually doing your mouth and tongue a favor.