Why are fried foods crispy?

Another good question from reader Bill. I’ll get into this a bit more later, however I think it’s a topic well worth discussing, since crispiness is the signature quality of fried (especially deep fried) food. Think corn dog, think french fry, think funnel cake, think…excuse me for a moment, I’m getting lightheaded…think fried chicken, think potato chip. None of these foods would be what they are without their signature crunch.

Yes, you can achieve crispiness in an oven, but usually not without drying out the food you’ve set out to crisp. That’s because (for reasons I shall get into) ovens cook foods far more slowly than hot oil. And that gives moisture more time to migrate out. If you’ve ever had an oven-baked doughnut you know exactly what I’m talking about. Deep frying, because of the density of the oil and the high temperature, cooks foods fast. Some moisture is lost in the process, of course, yet there simply isn’t enough time for all the water inside the food to escape before the cooking is done. This phenomenon is what gives fried food its signature moist interior (it’s not a result of fat as is popularly thought).

The moisture that does evacuate the food comes almost entirely from the very outer layer. Once immersed in the oil, the water there instantly boils and rushes away in bubbles of steam. Being devoid of all moisture, the surface is by definition dry. In other words, crisp.