Why Food Still Sticks to Nonstick Pans, According to Science

Last night, I fried up some plant-based burgers for dinner. Just as the instructions suggested, I used a nonstick pan. And just as I anticipated, the burgers stuck to the pan anyway. Why does this always happen? For years, I've been working under the theory that the people who sell nonstick pans are just big ol' liars. But this week, I've received a new answer: science! And thanks to a new paper titled "On formation of dry spots in heated liquid films," researchers even have some thoughts on how to prevent it.

According to the paper, published yesterday in the journal Physics of Fluids, scientists at the Czech Academy of Sciences used video to analyze the heating of sunflower oil in both a ceramic and a Teflon-coated nonstick pan. And they believe they caught their culprit. "We experimentally explained why food sticks to the center of the frying pan," author Alexander Fedorchenko stated. "This is caused by the formation of a dry spot in the thin sunflower oil film as a result of thermocapillary convection."

In plain English, the American Institute of Physics, which published the study, explained that as a film of oil is heated, surface tension decreases, a phenomenon that's usually strongest in the center of the pan where the temperature is highest. The resulting "thermocapillary convection" moves the oil outward and, eventually, the middle becomes thin enough that it "ruptures."

With this info in hand, the researchers then determined the specific conditions that create these sticky dry spots and offered up suggestions on how to prevent them. "To avoid unwanted dry spots, the following set of measures should be applied: increasing the oil film thickness, moderate heating, completely wetting the surface of the pan with oil, using a pan with a thick bottom, or stirring food regularly during cooking," Fedorchenko added.

And though not specifically mentioned in the paper, these findings may also encourage pan makers to consider producing pans with thicker bottoms to further prevent sticking. "My grandmother and mom used to use a heavy-bottomed pan and never had this problem. In addition, cast iron pans are usually used, which are wetted with oil," Fedorchenko told me via email. "Now I understand why. The thick bottom prevents large temperature gradients and, as a result, large surface tension gradients."

Meanwhile, if you really want to get into the weeds with the math, the authors also concluded, "For the heated thin film flowing down over a solid surface, the fundamental solution for free surface deformation has been derived. The solution shows that the spatial scale of the distortion Δxh = αlΔξ in the wide range of the volumetric flow rate change by three orders (q = 10−5 m2/s − 10−2 m2/s) for water remains of the order of the capillary length l: Δxh/l = 0.95 at q = 10−5 m2/s and Δxh/l = 2.04 at q = 10−2 m2/s. Together with the fulfillment of the condition hmin < hcr, this gives us the necessary conditions for the dry spot formation."

And you thought remembering how many teaspoons are in a tablespoon was a pain.