This word appears to be an example of syllabical incrementalization—a needless variant of crisp to be filed alongside orientate, mischievious, disassociate, preventative, and the like. What is the point of appending the adjectival suffix -y to a base that is already a perfectly good adjective?
I am not alone in this sentiment. A query that I posted on Ask-A-Linguist drew a response from Geoffrey Sampson suggesting that crispy is "an artificial word drawn from Chinese-restaurant vocabulary". "I am familiar with it," Sampson concedes, "but I would never think of using it myself." Our objection, however, turns out to be uninformed. According to the OED, the adjective crispy was not derived as a gratuitous extension of the adjective crisp, but rather as the adjectival form of the (now obsolete) noun crisp, denoting a curl of hair. Thus, crispy originally meant "curly" or "wavy", especially as applied to closely curled or frizzy hair, before acquiring its modern meaning. At some point, the noun came into use as an adjective as well, and the two have remained in concurrent use, although, as we shall see, not strictly synonomous.
The longer variant seems to have its own distinctive appeal. What accounts for the unbridled delight that it evokes in those who insist on using it? When I order "a dozen hot wings, well done, please" at a local sports bar, my server invariably asks for clarification—"You want them crispy?"—not because of any perceived ambiguity in my request; she simply won't be deprived of the euphony of the word. As celebrity chef Mario Batali observes, "The single word 'crispy' sells more food than a barrage of adjectives." Whatever the appeal may be, it has indeed been thoroughly exploited (and reinforced) by commercial advertising. Fried chicken chains have achieved success by touting their products as "extra crispy". On the supermarket breakfast cereal shelf we find Crispy Rice, Cocoa Crispy Brown Rice, Crispy Flakes and Fiber, Chocolate Cookie Crispy, Crispy Hexagons, and the ever popular Rice Krispies, whose distributors have been amply rewarded for both mispelling the word and transforming it into a noun. Inexplicably, Crispy Critters, in spite of its appealing name (better than the more standard "Crisp Creatures") was a commercial failure, although the phrase did catch on as military slang for badly burned corpses.
Marketers outside the food industry have curiously followed suit. The Web site of the brokerage Crispy-Hotels.com displays the motto "Stay well in a crispy hotel". The first name of the on-line swimwear shop Crispy Bikinis is reported also to be the nickname of its owner, who earned it by "showcasing her FUN [sic] quintessential California girl style, [and] true love of music, culture and fashion."
In the music world, we find the Extra Crispy Brass Band as well as the succinctly (crisply?) named Crispy, a Danish bubblegum dance act dedicated to "the world's bubbliest happiest bounciest music." The Japanese pop rock band Every Little Thing has released an album with the title "Crispy Park", intended to suggest "an enjoyable atmosphere that's both fresh and exciting."
No doubt, the excitement surrounding the word is closely tied to the allure of that which it describes. As Chef Batali goes on to say, "There is something innately appealing about crispy food." In fact, scientists of such diversity of perspective as anthropologist John Allen and food physicist Malcolm Povey agree that our taste for crisp food is derived from physiological responses to its characteristic sounds and their evolutionary implications. The fracturing that occurs as the teeth penetrate brittle food results in sudden drops in pressure, producing sound pulses covering a broad range of intensities and frequencies. A positive response to this stimulus has been rewarded through natural selection in a variety of ways. A taste for "fallback" foods such as roots and green vegetables was an evolutionary asset during times when more desirable fare was in short supply. With the advent of fire, cooking created a variety of crisp foods while making important nutrients more readily available, so that an appreciation for such food led to a more nutritious diet.
Given that our taste for crispness is strongly linked to auditory sensations, it is not surprising that we tend to describe it with onomatopoeic terms. The sound pulses that produce these sensations are naturally modeled by plosive consonants (such as p and hard c), sometimes in subtle ways. Povey compares the related terms crispy and crunchy and finds that the latter tends to be used in reference to foods that produce sounds of lower frequency than the former, in keeping with the relative frequencies found in the sounds of the words themselves. What can be said along these lines about crisp and crispy?
First, it is clear that the two variants are not interchangeable. One never hears of a "crispy autumn morning" or a "dry crispy Chablis". Only solid food is "crispy", and even within this domain, there is an important distinction in prevailing usage: brittle cooked foods are "crispy", whereas raw fruits and vegetables are "crisp". A Google search for "crisp apple", for example, produces references to fresh fruit, while "crispy apple" turns up tarts, pies, crumbles, and chips. This distinction in usage reflects a fundamental difference between the underlying biological and chemical phenomena. When a plant cell absorbs water through osmosis, its wall expands, exerting pressure on neighboring cells, which, in combination with the structural properties of the cell, accounts for the crispness of the plants. When a vegetable is cooked, the cell walls are destroyed and its structure deteriorates. But the cooking of many foods, especially roasting or frying at high temperatures, produces a sharp loss of water, mainly at the surface, resulting in a brittle texture. Thus, we have two very different sorts of crispness—one caused by the presence of water, the other by its absence. It is only natural to describe them with different terms.
But is there a natural basis for the allocation of these terms? Here it is tempting to follow Povey's lead and speculate that the meanings assigned to the two adjectives are somehow dictated by their onomatopoeic qualites. Neuroimaging research has shown that the processing of onomatopes activates the brain in the same ways as the stimuli that they denote. Perhaps we can agree that the dry crispness of cooked food is a stronger stimulus to the modern palate than the wet crispness of raw plants. (Of course, there remain those who claim to experience the same level of excitement in biting into a carrot or a leaf of lettuce that the rest of us enjoy in eating a slice of well-cooked bacon or a bag of Cheetos, but this is a rare and poorly understood breed, beyond the scope of this article.) Correspondingly, the audible release generated by a plosive consonant followed by a vowel is stronger than one that is in word-final position. Thus, crispy is the more onomatopoeic of the two words and is therefore naturally associated with the stronger stimulus.
In any case, if the original objective of this exercise was to establish a rational basis for my aversion to the word crispy, then it has been a dismal failure. Not only is the adjective found to be etymologically above reproach, but it provides a useful distinction in contraposition with crisp. Of course, none of this does anything to mitigate my instinctive distaste for the word—like Professor Sampson, I shall probably never use it myself—but I may have no choice but to tolerate it in the speech of those who do.