An investigation into how oils behave on hot, flat surfaces has uncovered the process responsible for food sticking to non-stick pans.
I like the opening line of this new one paper, published today in Physics of Fluids: “Here, the phenomenon of sticking food when frying in a pan is experimentally explained.”
Concise and straightforward, as is the explanation: “thermocapillary convection”, according to 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 while you are cooking, you can shake your angry fist on the stove and say, “Damn it, thermocapillary convection!” It will be a very satisfying moment, not only because you have a new fantasy 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 pans – one coated with ceramic particles and one coated with Teflon. The surfaces of the pans were covered with a thin layer of sunflower oil, and then, using a surveillance camera, the scientists measured the speed at which dry spots were needed to form and grow as the pans had were heated.
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The scientists noticed that while the pans were heated from the bottom, a temperature gradient appeared over the oily film. In turn, this created a surface tension gradient, which directed the oils away from the center of the vessel and to the periphery; liquids with high surface tension draw 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 this happens, the food is better suited to stick to the center of the pan, the result of “the formation of a dry spot in the thin film of sunflower oil,” according to the study.
Fedorchenko and Hruby actually created a formula to calculate the “wetting rate”, which measures the rate of withdrawal of oil droplets. Very cool, but the word “degeneration” 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 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, moderate heating, completely moisten the surface of the oil pan, use a thick-bottomed pan, mix the food regularly in cooking time “, write the authors.
Wow. I don’t know about you, but for me all this is extremely obvious advice (not to mention how the first and third items on the list are pretty much the same). Except for using thick-bottomed pans – I didn’t know that. But to be fair, I often used a cast iron skillet when frying food, so subconsciously I felt this was true.
Anyway, this makes me very hungry, so I will finish it right here, I will go to the kitchen and I will do my best to control the thermocapillary convection of idiosyncrasy.