Is there any truth in the phrase “hot enough to cook an egg on the sidewalk” (or the footpath as we call them in Australia)? I’ve often wondered this myself, and rather than just google it I thought it would be more interesting to try it and see the result with my own eyes.

The main ingredient - a hot day - was clearly present. Outside my home I measured the temperature as 41°C (105.8°F) in the shade, although I suspect it may have been closer to 42.9°C (109.2°F) which was the official Perth maximum. Whichever it was, it certainly qualified as hot.

I don’t have a footpath nearby, but the top of a low brick wall provided a flat surface with similar thermal properties. As for the egg, an old one in the back of the fridge, a year past its use by date, was a perfect candidate. I could use it in an experiment without feeling I was wasting it.

Having cracked the egg on the bricks, I photographed it at intervals to record the changes (click on photos to see a larger version). The egg white stopped spreading out within a minute, and the yolk firmed noticeably within two. It looked hopeful! After a promising start, however, further progress was disappointing. Even after half an hour most of the whites were still gooey and not white.

When I eventually scraped the egg off the bricks after two hours, the whites were mostly firm but not properly cooked. The yolk looked almost edible, but as the egg was so old, not to mention contaminated by dirt and bits of brick, I didn’t fancy eating it. I concluded that hot bricks (equivalent to a sidewalk) are not a viable way of cooking an egg, even if you overlook practicalities like hygeine.

Back inside, I consulted the internet. According to the US Library of Congress, eggs need a temperature of at least 70°C (158°F) to properly cook. Also:

“Once you crack the egg onto the sidewalk, the egg cools the sidewalk slightly. Pavement of any kind is a poor conductor of heat, so lacking an additional heat source from below or from the side, the egg will not cook evenly.
Something closer to the conditions of a frying pan would be the hood of a car. Metal conducts heat better and gets hotter, so people actually have been able to cook an egg on a car hood’s surface.”

I couldn’t get a reliable temperature reading of the bricks, but suspect they weren’t hot enough. The roof of a car is a much better idea. Any car parked in the sun during a Perth summer can get up to 60°C (140°F) inside, and I’ve measured this in my own car often enough. The roof should be hotter, and with some aluminium foil and a little oil, I expect an egg would cook more effectively there than on brick … probably good enough to eat.

I’ll try egg-cooking on a car another time. For now I plan to stay in the only sensible environment in such hot weather - indoors.