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In The Babbo Cookbook, the celebrity chef and restaurateur Mario Batali wrote, "The single word 'crispy' sells more food than a barrage of adjectives. ... There is something innately appealing about crispy food." The hypothesis that crispy foods are innately appealing is a fascinating one. As an anthropologist interested in the evolution of cognition and the human diet, I think that maybe our attraction to crispy foods could give us insights into how people have evolved to think the food that they eat.

Perhaps one reason that crispy foods have such an appeal lies in their ability to stimulate our hearing as well as our senses of taste and smell. Crispiness in and of itself stands apart from other food qualities; this texture can be pleasurable even when combined with flavors that are themselves not necessarily all that appealing. Chewing crispy foods is louder than chewing noncrispy foods. If habituation [sensory neurons usually become less responsive with persistent exposure to a stimulus] takes longer given a stronger sensory signal, then we should enjoy eating crispy foods for a longer period of time during any given bout of eating. Of course, numerous factors are important in determining what we like to eat, but it is not unreasonable to suggest that we might like a particular crispy food in part because we like the way it sounds in our own heads.

Simply reading, hearing, or saying the onomatopoeic terms "crispy" and "crunchy" is likely to evoke the sense of eating that type of food. Presumably this feeling would be represented in the brain by activation of the mouth and tongue regions of the primary motor cortex (and of course, when a word is actually said, the motor regions of the mouth are being directly activated). "Crispy" might be such a compelling descriptive term because, in a sense, hearing or saying it strongly promotes the motor imagery of eating—a food item with the word "crispy" attached to it is in some ways already being eaten by its potential consumer. "Crispy" in a menu could be quite persuasive, especially when coupled with the fact that crispy foods are often quite palatable for other reasons.

Hmm... that's a really good question. Your basic flavor stuff is all based on nutritional needs: sweet, salty, sour, bitter and umami are all things you need (bitter as a deterrent to eating has been disproven, the vitamins and antioxidants in fruits are mainly bitter), and there's evidence that long-chain fats have their own receptors other than a generic "creamy" sensation.

But while crunchy is common in nature (a few fruits, a lot of vegetables), the more delicate but harder materials called crispy really don't. Only when you start processing foods do you approach crispy: well-done bacon and bread crust are probably the simplest, most others involve frying, I think.