Scientists have gotten to the bottom of why food still sticks to ‘non-stick’ pans

Scientists have revealed why food sticks to non-stick pans – a problem that plagues chef and home cook kitchens alike.

Fluid mechanics experts at the Czech Academy of Sciences say oil in frying pans diffuses outward, leaving dry patches in the center for food to stick to.

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

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

However, the problem can be solved by completely wet the surface of the non-stick pan before cooking.

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“ To avoid unwanted dry spots, the following measures should be taken – increase the oil film thickness, moderate heating, wet the surface of the pan completely with oil, use a pan with a thick bottom, or stir frequently while cooking, ” said study author Alexander Fedorchenko.

Non-stick cookware has an all-important coating made from a chemical called polytetrafluoroethylene (PTFE).

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

Food sometimes sticks to a heated surface, even when using oil and a non-stick frying pan, meaning we have to scrape our meals onto our plates, often with an unsavory result.

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

The experimental study used a non-stick pan with a surface consisting of ceramic particles, as well as a pan with Teflon coating.

Ceramic cookware also has a non-stick coating, but it 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 decreased immunity.

A video camera, placed above the pans during heating, was used to measure the speed at which a dry patch formed and grew.

Video images from the researchers show that the dry spot spreads from the center of the ceramic pan in just four seconds.

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

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

‘This is caused by the formation of a dry spot in the thin film of sunflower oil as a result of thermocapillary convection.’

Researchers have broken down the liquid process into steps – essentially, when a pan is heated from the hob below, a temperature gradient is established in the film of the cooking spiral.

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

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

This gradient creates thermocapillary convection, which moves oil out.

When the oil film in the center becomes thinner than a critical value, the film tears, exposing the dreaded dry spot.

The researchers also determined the conditions that lead to dry spots for both stationary and fluid films, detailed in their paper, which is 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 under a number known as the capillary length.

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

“Dry spotting or film breakage plays a negative role, resulting in severe overheating of the electronic components,” Fedorchenko said.

‘The results of this research can therefore be applied more widely.’