Tag Archives: temperature rise

Sunny side up: Can you really fry an egg on the footpath on a hot day?

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Ah, the Australian summer. When the temperatures top 40℃ and only the bravest or most foolhardy would venture outside in bare feet, there’s a cherished old saying: “It’s so hot outside, you could fry an egg on the footpath!”

But what does the science say? Does this claim stack up, or it half-baked?

To answer this question, we need to understand the chemicals inside an egg, what happens to them during the cooking process, and whether the footpath really gets hot enough to drive these chemical changes.

The first and most obvious point is that the egg’s yolk and white are chemically very different. The white, which makes up about two-thirds of an egg’s mass, is roughly nine parts water and one part protein. The key here is that the protein’s structure changes if you heat it above a certain temperature.

Omelette on road/Photo: Shutterstock

About half the yolk’s mass is water, about a quarter is “fat”, about one-sixth is protein, and less than 5% is carbohydrates. The protein in the yolk is a completely different type of protein, but much like with the egg white, it’s how the protein responds to heat that gives us the texture of fried, scrambled, poached or hard-boiled eggs.

Ok, so how does this work?

We can think of proteins as being long chains of molecules called amino acids. In a raw egg, the protein is suspended in the watery mixture. The chain is curled up in a very particular way, held in shape by weak chemical bonds between different parts of the chain as it folds over on itself. (The animation below shows the folded structure of ovalbumin, the main protein in egg white.) This keeps it stable, and able to mix with the water.

But once it’s heated up, the heat energy starts to break these weak chemical bonds and the chain begins to uncurl, rearrange itself and stick together again in a completely different way.

Suddenly, these reconfigured clumps of protein molecules are no longer water-soluble, so they solidify. This is why eggs get harder if you cook them for longer.

This process is called denaturation, and it can happen to any type of protein. Denaturation is what turns milk into curds and whey, and changes the texture of meat as it cooks.

For eggs, denaturation begins at around 60℃, but this is likely to only slightly cook the egg whites, and the yolk will not turn solid at all.

As you slowly go from 60℃ to 70℃, however, there’s more heat energy available, and all of the egg’s proteins now begin to denature. The egg white begins to turn gel-like and eventually rubbery, and the yolk begins to solidify into a viscous goo, before eventually becoming solid or even slightly powdery in texture.

Get the temperature right and this process unfolds nice and gradually, which means with a bit of practice you can get your eggs to turn out exactly how you like them.

Right, so is a footpath hot enough for this?

That leaves us with the crucial question: How hot does pavement get on a scorching summer day? Does it reach the almost 70℃ you would need for a footpath fry-up?

This depends on a lot of factors, including the air temperature, direct sunlight, the footpath material, and even its colour. Black-painted concrete, for example, absorbs more heat than white or unpainted concrete.

All in all, at the peak of these conditions, on a boiling summer day, a footpath can potentially just about reach the right temperature. But sadly, that’s still not enough to sizzle an egg.

First, concrete is a poor conductor, so it will transfer heat to the egg much more slowly than a metal frying pan. Second, after cracking the egg onto the footpath, the footpath’s temperature will drop slightly.

Temperature swings to hit southern hemisphere, including India hardest

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Temperature fluctuations that are amplified by climate change will hit India and other countries hardest, said a new research.

It found that every additional degree of global warming triggers increase in temperature by up to 15% in southern Africa and Amazonia, and up to 10% in the Sahel, India and South East Asia.

Meanwhile, countries outside the tropics – many of which are richer countries that have contributed most to climate change – should see a decrease in temperature variability.

The researchers, from the universities of Exeter, Wageningen and Montpellier, discovered this “unfair pattern” as they addressed the difficult problem of predicting how weather extremes such as heat waves and cold snaps might change in a future climate.

“The countries that have contributed least to climate change, and have the least economic potential to cope with the impacts are facing the largest increases in temperature variability,” said lead author Dr Sebastian Bathiany, of Wageningen University.

Co-author Professor Tim Lenton, from the University of Exeter, added: “The countries affected by this dual challenge of poverty and increasing temperature variability already share half of the world’s population, and population growth rates are particularly large in these countries.”

“These increases are bad news for tropical societies and ecosystems that are not adapted to fluctuations outside of the typical range.”

Relative change in standard deviation of monthly temperature anomalies until the end of the 21st century versus per capita GDP in different countries. The red line marks zero change in temperature variability. The blue line marks half of the current world population. Credit: Sebastian Bathiany, Wageningen University

The study also reveals that most of the increased temperature fluctuations in the tropics are associated with droughts – an extra threat to food and water supplies.

For their investigation, the team analysed 37 different climate models that have been used for the last report of the Intergovernmental Panel on Climate Change (IPCC).

Although climate variability has been studied extensively by climate scientists, the fact that climate variability is going to change has received little attention in fields investigating the impacts of climate change.