While you can certainly fry food in hot oil as is (think skin-on chicken pieces), we often dip food in a coating first. Such coatings provide a few benefits: They help protect the food from moisture loss, and they shield the food from direct contact with the hot frying oil for more gentle cooking. And perhaps most important, we know that these coatings—starchy coatings, specifically—become incredibly crispy when fried. But until now we’ve never really asked ourselves the deeper question: What exactly is happening that makes starch the key?
Here’s what we’ve learned. First, the starch granules in the coating absorb water, whether from the wet surface of the food itself or because they are combined with a liquid to make a slurry before coating the food (as we do for our Thick-Cut Sweet Potato Fries; see related content). The hydrated granules swell when they are initially heated in the oil, allowing the starch molecules to move about and separate from one another. As water is driven away during the frying process, these starch molecules lock into place, forming a rigid, brittle network with a porous, open structure.
Furthermore, the two types of starch molecules (amylose and amylopectin) form some cross-links with one another at high frying temperatures, further reinforcing the coating’s structure. Thus, the molecules in this porous network have room to compress and fracture, providing the sensation of crispiness. Interestingly, cornstarch contains 25 to 28 percent amylose, which is higher than the amount in wheat or potato starch (which are 20 to 22 percent amylose), and this is why cornstarch works the best for making crispy coatings on fried foods.
I'm quite familiar with the science behind frying food and the role that starchy coatings play in creating that irresistible crispiness. The process involves a deep understanding of starch granules, their behavior when exposed to heat and oil, and how they contribute to the texture of fried foods. Here's a breakdown of the concepts touched upon in the article:
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Starch Granules and Water Absorption: Starch granules, found in coatings, absorb water when they come into contact with moisture from the food's surface or when combined with a liquid to form a slurry. This hydration causes the granules to swell.
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Swelling and Starch Molecule Separation: When these hydrated granules are heated in oil, they undergo swelling, allowing the starch molecules to separate from one another as water evaporates during frying.
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Formation of Rigid Structure: As water is driven off, the starch molecules lock into place, forming a rigid, brittle network with a porous structure. This structure is crucial in achieving crispiness.
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Cross-Linking of Starch Molecules: Amylose and amylopectin, the two types of starch molecules, form cross-links at high frying temperatures. These links further strengthen the coating's structure.
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Porous Network and Crispiness: The porous network formed by starch molecules allows for compression and fracturing, which is what provides the sensation of crispiness when the food is fried.
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Amylose Content in Cornstarch: Cornstarch contains a higher percentage of amylose (25 to 28 percent) compared to wheat or potato starch (20 to 22 percent amylose). This higher amylose content is why cornstarch is particularly effective in creating crispy coatings on fried foods.
Understanding these concepts is crucial in optimizing recipes for crispy fried foods. It's fascinating how the molecular behavior of starch under specific frying conditions contributes to the texture we enjoy.
