Scientists have determined why food still sticks to ‘non-stick’ pans

Scientists have revealed why food sticks to non-stick pans – an issue that plagues the kitchens of chefs and home cooks.

Flow mechanics experts from the Czech Academy of Sciences say oil in frying pans is spread outwards, leaving dry spots in the middle to stick to food.

This is the result of a process called thermocapillary convection – where liquid such as oil flows under a certain temperature from low surface tension areas to high surface area areas.

The problem affects normal frying pans and even pans that are marketed as ‘non-stick’, containing ceramics or a layer of non-stick chemicals.

However, the experts claim that the surface of the non-stick pan is wetted before you start cooking anything.

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To avoid unwanted dry spots, the following measures should be applied: increase the thickness of the oil oil, moderate heating, completely wet the surface of the pan with oil, use a pan with a thick bottom or stir food frequently during cook. said study author Alexander Fedorchenko.

Non-stick cookware contains an important layer made of a chemical called polytetrafluoroethylene (PTFE).

PTFE is marketed by an American chemical company as ‘Teflon’ – and it is also known by this name.

Food will sometimes stick to a heated surface, even if oil and a non-stick frying pan are used, which means we have to scrape our meals off our plate, often with unsophisticated results.

Therefore, researchers from the Czech Academy of Sciences wanted to investigate the liquid properties of oil on a flat surface, such as a frying pan.

The experimental investigation used a non-stick pan with a ceramic particle surface, as well as a Teflon-coated pan.

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

A video camera placed above the pans while heated was used to measure the velocity at which a dry spot formed and grew.

Video footage of the researchers shows how the dry spot spreads within four seconds from the center of the ceramic pan.

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

“We explained experimentally why food sticks in the middle of the frying pan,” Fedorchenko said.

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

Researchers have broken up the liquid process into steps – in essence, a temperature variation is determined in the film of coil when a pan is heated from the hob.

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

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

This gradient sets up the thermocapillary convection, which moves 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 still and flowing films, as outlined in their paper, published in Physics of Fluids.

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

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

“Dry spot formation or film breakage plays a negative role, leading to sharp overheating of the electronic components,” Fedorchenko said.

“The results of this study can therefore be applied more widely.”