Scientists have discovered why foods still stick to “non-stick” pans

Scientists have revealed why food sticks to nonstick pans – a problem plaguing the kitchens of chefs and home cooks.

Fluid mechanics experts at the Czech Academy of Sciences say the oil in the frying pans is spread out, leaving dry spots in the center for food adherence.

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

The problem affects normal frying pans and even frying pans sold as ‘nonstick’, which contain ceramic or have a layer of glue-resistant chemicals.

Completely moistening the surface of the nonstick skillet before you start cooking anything can solve the problem, experts say.

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

Non-stick cooking utensils have a very important coating made from a chemical called polytetrafluoroethylene (PTFE).

PTFE is marketed by a chemical company in the United States as ‘Teflon’ – and is often known by that name.

Food is sometimes stuck to a heated surface, even if you use oil and a non-stick frying pan, which means that we have to scrape our meals on our plate, often with unappetizing results.

The 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 pan with a surface composed of ceramic particles, in addition to a pan coated with Teflon.

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

A video camera, placed above the pots as they were heated, was used to measure the speed at which a dry spot formed and grew.

Video footage of the researchers shows the dry stain spreading from the center of the ceramic tray in just four seconds.

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

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

“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 stages – essentially, when a pan is heated on the plate below, a temperature gradient is established in the film of the cooking coil.

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

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

This gradient sets up the thermocapillary convection, which moves the oil out.

When the oil film in the middle 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 stationary films and fluids, detailed in their article, 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 a capillary length.

The 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 breakage of the film plays a negative role, resulting in a strong overheating of the electronic components,” said Fedorchenko.

‘The results of this study may therefore have a wider application.’