A study of the way oil behaves on a hot, flat surface has uncovered the process responsible for foods that adhere to non-stick frying pans.
I love the opening line for this new thing paper, published today in Wet Physics: “Here we explain how food sticks when it is being served in a frying pan.
Short and straight to the point, as the definition: “thermocapillary convection,” according to the authors, Alexander Fedorchenko and Jan Hruby, both of the Czech Academy of Sciences.
This is a very powerful experience. The next time this happens when you are cooking, you can shake your angry fist at the stove and say, “curse, thermocapillary convection! “It will be a very happy time, not only because you have an exciting new term, but also because you are fully aware of what it means.
For their experiment, Fedorchenko and Hruby, experts in fluid dynamics and thermophysics, tested two non-stick frying pans – one coated in ceramic grains and one coated with Teflon. The surface of the pans was covered with a thin layer of sunflower oil, and then, using an overhead camera, the scientists measured the speed at which it took dry spots to form and growing as the pans were heated.
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The scientists noticed that as the pans warmed up below, a temperature gradient appeared throughout the oily film. This created a gradient of surface tension, which directed the wool away from the center of the pan and toward the edge; elevators with high surface tension draw more on elevators around them compared to elevators with low surface tension.
This is a good example of thermocapillary contact at work – a phenomenon where the gradient of surface tension causes a liquid (in this case, oil) to migrate out. As soon as this happens, food is more suitable for sticking to the center of the pan, the result of “creating a dry place in the thin sunflower oil film,” according to the study.
Fedorchenko and Hruby have actually developed a formula for measuring “melting rate,” which measures the rate at which oil droplets are decaying. Pretty cool, but the word “dewetting” is something we don’t need in our lives right now. The scientists also identified the conditions that cause dry spots, and followed the following advice:
“To avoid the formation of an unwanted dry spot, the following set of measures (and / or) should be applied: increase the thickness of the oil film, moderate heating, wet the surface of the pan completely with oil, using a pan with thick base, moving food regularly during cooking, ”the authors write.
Wow. I don’t know about you, but for me that’s all clear advice (not to mention how the first and third things on that list are the same thing). As well as using pans with a thick bottom – I didn’t know it. But to be fair, I used to use an iron pan often when frying foods, so I have to feel that this was true.
Anyhoo, all of this makes me really hungry, so I’m going to finish this, go to the kitchen, and do my best to match a collection thermocapillary idiosyncrasies.