Research on the behavior of oils on flat, hot surfaces has uncovered the responsible process of foods adhering to non-stick pans.
I love the opening line of this new one paper, published today in Physics of Fluids: “Here the phenomenon of food adhesion when fried in a frying pan is explained experimentally.”
Concise and direct to the point, as is the explanation: “thermocapillary convection,” according to the authors, Alexander Fedorchenko and Jan Hruby, both of the Czech Academy of Sciences.
This is a very powerful knowledge. The next time this happens while you’re cooking, you can shake your angry fist in the kitchen and say, “Damn it, thermocapillary convection!” It will be a very satisfying time, not only because you have a new term at your disposal, but also because you are fully aware of what it really means.
For their experiment, Fedorchenko and Hruby, specialists in fluid dynamics and thermophysics, tested two non-stick pans, one coated with ceramic particles and another covered with Teflon. The surfaces of the pans were covered with a thin layer of sunflower oil and then, using a camera, the scientists measured the speed at which dry spots were taken to form and grow as they that the pans were heated.
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Scientists noticed that as the pans were heated from below, a temperature gradient appeared on the oily film. In turn, this created a surface tension gradient, which directed the oils away from the center of the pan and toward the periphery; liquids with high surface tension stretch the surrounding liquids more strongly compared to liquids with low surface tension.
This is an excellent example of thermocapillary convection at work: a phenomenon in which a surface tension gradient forces a liquid (in this case, oil) to migrate outward. Once that happens, the food is more likely to stick to the center of the pan, resulting in the “formation of a dry spot on the thin film of sunflower oil,” according to the study.
Fedorchenko and Hruby actually created a formula for calculating the “dew rate,” which measures the speed of oil droplets. Very cool, but the word “disorient” is something we don’t need in our lives now. Scientists also identified conditions that lead to dry spots, leading to the following tips:
“To avoid the formation of unwanted dry spots, the following set of measures (and / or) must be applied: increase the thickness of the oil film, heat it moderately, completely wet the surface of the frying pan with oil, using a frying pan with a thick bottom, stirring food regularly during cooking ”, write the authors.
Wow. I don’t know about you guys, but to me this is incredibly obvious advice (not to mention how the first and third items on this list are basically the same). Except for using pans with a thick bottom, I didn’t know it. But to be fair, I often used a cast iron skillet when frying food, so I unconsciously must have felt that this was true.
Anyhoo, all of this makes me very hungry, so I’ll end up right here, go to the kitchen, and do my best to master the thermocapillary convection of idiosyncrasy.