A study of the way oils behave on hot, flat surfaces has uncovered the process responsible for food sticking 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 sticking during frying in a skillet is experimentally explained.”
Concise and straight to the point, as the explanation is: “thermocapillary convection”, say the authors, Alexander Fedorchenko and Jan Hruby, both from the Czech Academy of Sciences.
This is a very powerful knowledge. The next time this happens in cooking, shake your angry fist at the stove and say, “damn you, thermocapillary convection!” It will be a very satisfying moment, not only because you have a beautiful new term at your disposal, but also because you are fully aware of what it actually means.
For their experiment, Fedorchenko and Hruby, specialists in fluid dynamics and thermophysics, tested two non-stick frying pans: one covered with ceramic particles and one covered with Teflon. The surfaces of the pans were covered with a thin layer of sunflower oil, and then, using a camera above their heads, the scientists measured the rate at which dry patches were required to form and grow while the pans were heated.
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The scientists noted that while the pans were heated from below, a temperature gradient appeared across the oily film. This, in turn, created a surface tension gradient that carried the oils away from the center of the pan to the periphery; liquids with a high surface tension are more powerful against surrounding liquids compared to liquids with a low surface tension.
This is an excellent example of thermocapillary convection at work – a phenomenon where a surface tension gradient forces a liquid (in this case oil) to migrate outward. Once this happens, the food is more likely to stick to the center of the pan, the result of “the formation of a dry patch in the thin film of sunflower oil,” the study said.
In fact, Fedorchenko and Hruby came up with a formula to calculate the “dewatering rate,” which measures the speed of retreating oil droplets. Very cool, but the word “dewatering” is something we don’t need in our lives right now. The scientists also identified the conditions that lead to dry patches, which resulted in the following advice:
“To prevent unwanted dry spot formation, the following measures (and / or) should be applied: increase the oil film thickness, moderate heating, completely moisten the surface of the pan with oil, use a pan with a thick bottom, stir food regularly during cooking, ”the authors write.
Wow. Don’t know about you, but to me, that’s all strikingly obvious advice (not to mention the first and third items on that list are essentially the same thing). I didn’t know that except pans with a thick bottom. But to be fair, I often used a cast iron pan when baking food, so I must have unconsciously felt this to be true.
Anyway, this all makes me very hungry, so I’m going to end it here, go to the kitchen, and do my best to get the hang of the thermocapillary convection quirks.