An investigation into the behavior of oils on hot, flat surfaces has revealed the process responsible for food sticking to non-stick frying pans.
I love the opening line for this new one paper, published today in Physics of Fluids: “Here, the phenomenon of food sticking when frying in a frying pan is explained experimentally.”
Concise and to the point, as is the explanation: “thermocapillary convection”, according to authors Alexander Fedorchenko and Jan Hruby, both from the Czech Academy of Sciences.
This is very powerful knowledge. The next time this happens while cooking, you can shake your furious fist at the stove and say, “Damn it, thermocapillary convection!” It will be a very rewarding time, not only because you have a sophisticated new term at your disposal, but also because you will be fully aware of what it really means.
For their experiment, Fedorchenko and Hruby, specialists in fluid dynamics and thermophysics, tested two non-stick frying pans – one coated with ceramic particles and the other covered with Teflon. The surfaces of the pans were covered with a thin layer of sunflower oil and then, using an overhead camera, the scientists measured the speed at which dry spots formed and grew as the pans were heated.
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Scientists noted that as the pans were heated from below, a temperature gradient appeared in the oily film. This, in turn, created a gradient of surface tension, which directed the oils away from the center of the pan and towards the periphery; liquids with a high surface tension pull the surrounding liquids harder than liquids with a low surface tension.
This is an excellent example of thermocapillary convection in operation – a phenomenon in which a gradient of surface tension forces a liquid (in this case, oil) to migrate outward. When this happens, the food is more likely to stick to the center of the pan, the result of “the formation of a dry spot on the thin film of sunflower oil”, according to the study.
Fedorchenko and Hruby actually created a formula to calculate the “dew rate”, which measures the speed of the recoil of the oil drops. Very cool, but the word “redness” is something we don’t need in our lives right now. Scientists have also identified the conditions that lead to dry spots, resulting in the following advice:
“To avoid the unwanted formation of dry stains, the following set of measures (and / or) should be applied: increase the thickness of the oil film, moderate heating, completely moisten the surface of the pan with oil, use a pan with a thick bottom , stir food regularly during cooking ”, write the authors.
Wow. I don’t know about you, but for me this is extremely obvious advice (not to mention how the first and third items on this list are basically the same thing). Except for using pans with a thick bottom – I didn’t know that. But to be fair, I often used a cast iron skillet to fry food, so I must have unconsciously felt that this was true.
Anyway, this is making me very hungry, so I’ll finish right here, go to the kitchen and do my best to master the idiosyncrasies of thermocapillary convection.