Nothing ruins a good meal like immediately burning the roof of your mouth with too-hot food. But what is “too-hot”? Well, drinking beverages or eating foods at anywhere above 110°F runs the risk of irritating your mouth, but consuming anything at 160 degrees or hotter usually equals an immediate burn. Now, while no one can exactly calibrate the temperature of the food or drink they’re taking in, most folks realize that if a cup or plate of something is steaming, it’s likely hot enough to scald you. So, we all will do what if we see that steaming food or drink? We’ll, out of instinct or habit, blow on it. But does blowing on hot foods & drinks really help to cool them off, or are we just blowing hot air?
Well, the answer is: yes…to both questions.
When you blow air over piping hot food, you’re moving air that’s about the same as that of your own body temperature (98.6 degrees on average) to replace warmer air. It’s what’s known as “convection”. Because the air around the mug or plate is cooler after you blow, it increases the rate of heat transfer. Think of it this way: if you had a bowl of soup in a warm room, it would take a longer time to cool down. But if that same bowl were placed in an unheated room, it would cool off much more quickly. The reverse is also true, though: imagine an ice cream cone that quickly melts on a steamy summer day versus one that stays pretty much intact when you’re inside on a cool winter night.
When left alone, food will still lose heat by transferring energy into a bowl, otherwise known as conduction. Blowing on it speeds that up. When you blow on food with a lot of moisture, you can also enact “evaporative cooling”, when your breath moves the water vapor away from the surface of the heated element, allowing more of the water molecules to evaporate. Think blowing puffs of steam away from your cup of tea. And because evaporative cooling is more effective, it’s easier to cool liquids than solid foods. You can also help food cool off by breaking it up into smaller pieces, so that they retain less heat. And the hotter the food or drink, the more of a difference in temperature, so blowing on hot stuff is best. If something is merely warm, there may not be enough of a disparity in heat to make a difference.
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