Scientists have reached the bottom of why foods still adhere to “non-stick” pans

Scientists have revealed why food sticks to non-stick pans, a problem that affects cooks ’and home cooks’ kitchens.

Experts in fluid mechanics from the Academy of Sciences of the Czech Republic claim that the oil from the pans disperses to the outside, leaving dry spots in the center where the food sticks.

This is the result of a process called thermocapillary convection, where, at a given temperature, liquid such as oil flows from areas of low surface tension to areas of high surface tension.

The problem affects normal pans and even pans marketed as “non-stick,” which contain pottery or contain a layer of stick-resistant chemicals.

Completely wetting the surface of the non-stick pan before starting to cook anything can solve the problem, however, experts say.

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“To avoid unwanted dry stains, the following set of measures should be applied: increase the thickness of the oil film, heat it moderately, completely wet the surface of the pan with oil, use a frying pan with a thick bottom or stir the food regularly during cooking “. said the author of the study Alexander Fedorchenko.

Non-stick kitchen utensils have a significant coating from a chemical called polytetrafluoroethylene (PTFE).

An American chemical company markets PTFE under the name “Teflon”, and it is often known by that name.

Sometimes food sticks to a heated surface, even if oil and a non-stick frying pan are used, meaning we have to scrape food on the plate, often with unattractive results.

Researchers at the Czech Academy of Sciences therefore wanted to investigate the fluid properties of oil on a flat surface, such as a frying pan.

The experimental research used a non-stick pan with a surface made up of ceramic particles, as well as a Teflon-coated pan.

Ceramic cookware is also non-stick, but does not contain PTFE or other chemicals in Teflon pans such as perfluorooctanoic acid (PFOA), which has previously been linked to cancer, high cholesterol, and reduced immunity.

To measure the speed at which a dry spot formed and grew, a video camera placed over the pans was used as they warmed up.

Video images of the researchers show the dry stain extending from the center of the ceramic pot in just four seconds.

Other experiments with a Teflon-coated frying pan showed the same results.

“Experimentally we explained why food sticks to the center of the pan,” Fedorchenko said.

“This is caused by the formation of a dry spot on the thin film of sunflower oil as a result of thermocapillary convection.”

The researchers divided the fluid process into steps: essentially, when a pan is heated from the bottom plate, a temperature gradient is set on the film of the cooking coil.

For common liquids, such as sunflower oil used in the experiment, surface tension decreases as the temperature rises.

A surface tension gradient is established directed towards the center where the temperature is higher and towards the limit of the pan.

This gradient establishes thermocapillary convection, which moves the oil outward.

When the oil film in the middle becomes thinner than a critical value, the film breaks and exposes the dreaded dry spot.

The researchers also determined the conditions leading to dry spots for stationary and fluid films, detailed in their paper, published in Physics of Fluids.

These conditions include a decrease in the local thickness of the film below a critical size, as well as the size of the deformed region falling below a number known as hair length.

Researchers say the phenomenon also occurs in other situations, such as thin liquid films used in fluid distillation columns or other devices that may have electronic components.

“The formation of dry spots or the rupture of the film plays a negative role, which causes intense heating of electronic components,” said Fedorchenko.

“The results of this study may therefore have a broader application.”