Scientists have reached the bottom of why food remains in non-stick pans

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

Experts in fluid mechanics from the Czech Academy of Sciences say that the oil in the pan is dispersed to the outside, leaving dry stains in the center to stick to food.

This is the result of a process called thermocapillary convection – in which, at a certain temperature, liquid, such as oil, flows from areas with low surface tension to areas with high surface tension.

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

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

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“To avoid unwanted dry stains, the following set of measures should be applied – increasing the thickness of the oil film, moderate heating, completely wetting the surface of the pan with oil, using a thick-bottomed saucepan or mixing food regularly during cooking.” said the author of the study Alexander Fedorchenko.

Non-stick cookware has a very important coating of a chemical called polytetrafluoroethylene (PTFE).

PTFE is marketed by a US chemical company as “Teflon” – and is often known as this.

The food will sometimes stick to a heated surface, even if oil and a non-stick pan are used, which means that we have to scrape our meals on the plate, often with unpleasant results.

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

The experimental investigation used a non-stick tray with a surface made of ceramic particles, as well as a tray covered with Teflon.

Ceramic vessels are non-stick, but do not contain PTFE or other chemicals in Teflon vessels, such as perfluorooctanoic acid (PFOA), which has previously been linked to cancer, high cholesterol and low immunity.

A video camera, placed above the pans while they were heated, was used to measure the speed at which it formed and increased a dry point.

The researchers’ video footage shows the dry stain spreading from the center of the ceramic vessel in just four seconds.

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

“We explained experimentally why food sticks to the center of the pan,” Fedorchenko said.

“This is caused by the formation of a dry spot in the thin film of sunflower oil due to thermocapillary convection.”

The researchers decomposed the fluid process into stages – essentially, when a pan is heated on the stove below, a temperature gradient is established in the film of the cooking coil.

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

A surface tension gradient is established, directed away from the center where the temperature is higher and towards the edge of the pan.

This gradient configures the thermocapillary convection, which moves the oil outwards.

When the middle oil film becomes thinner than a critical value, the film breaks, exposing the dreaded dry stain.

The researchers also determined the conditions that lead to dry spots for both stationary and flowing films, detailed in their paper, which was published in Physics of Fluids.

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

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

“The formation of dry spots or breaking of the film plays a negative role, leading to strong overheating of electronic components,” said Fedorchenko.

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