This question comes from the saying “It’s so hot you
could fry an egg on the sidewalk!” How many kids, hearing
it, actually try? Most likely they end up with a mess resembling
scrambled eggs more than one sunny-side up. So what’s the
An egg needs a temperature of 158°F to become firm. In order
to cook, proteins in the egg must denature (modify), then coagulate,
and that won’t happen until the temperature rises enough
to start and maintain the process.
The sidewalk presents several challenges to this. According to
an experiment reported in Robert Wolke’s book, What Einstein
Told His Cook: Kitchen Science Explained, sidewalk temperatures
can vary depending on the composition of the sidewalk, whether
it is in direct sunlight, and of course, the air temperature. Dark
objects absorb more light, so blacktop paving would be hotter than
concrete. More often than not, sidewalks are concrete. Wolke found
that a hot sidewalk might only get up to 145°F. 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.
Still, the idea of cooking an egg on a sidewalk won’t die.
It is so intriguing that the city of Oatman, Arizona, hosts an
annual Solar Egg Frying Contest on the 4th of July. Contestants
get 15 minutes to make an attempt using solar (sun) power alone.
Oatman judges, however, do allow some aids, such as mirrors, aluminum
reflectors, or magnifying glasses, which would help to focus the
heat onto the egg itself. It turns out that eggs also have a bit
of an advantage in Arizona, the land of low humidity and high heat.
Liquids evaporate rapidly when humidity is low. The eggs have a
bit of “help” while they cook, and they dry out faster.
I bet you were wondering what is the origin of the saying? It’s
not clear, although there is a reference to it in the Los Angeles
Times on October 5, 1933, and even as far back as June 11, 1899,
in The Atlanta Constitution--so the idea had captured the American
imagination and become one of our common sayings by that time.
And what about the other saying, “it’s so hot the chickens
are laying hard-boiled eggs?” Well, what do you think?
Peter. Heating and eating: physical gastronomy. In his The
science of cooking. Berlin, New York, Springer,
c2001. p. 37-52
of heat and mass transfer. 6th ed. Frank P. Incropera
and others. Hoboken, NJ, John Wiley, c2007.
Gale encyclopedia of science. Edited by K. Lee
Lerner and Brenda Wilmoth Lerner. 3rd ed. Detroit,
Gale, c2004. See p.1948-1951 for articles about heat.
Daniel, and Gregg Stebben. Heat. In his Everything
you need to know about physics. NY, Pocket Books,
c1999. p. 61-69.
Nuys about ready to fry eggs on walks. Los Angeles
times, October 5, 1933: 6.
Francis Henry. How to keep cool. The Atlanta constitution,
June 11, 1899: A6.
Robert L. What Einstein told his cook: kitchen science
explained. New York, W. W. Norton & Company,
more print resources...
Search on "Cookery," "Heat--Transmission," or “Physics—Popular
in the Library of Congress Online
Even with the tin foil and the temperature
in the high 90s, this egg is not getting cooked. Photo courtesy
of MJ Cavallo.
egg cooking in the water of Hot Creek Gorge thermal area, California. USGS Web
frying eggs on cement wall near U.S. Capitol. Prints & Photographs
Division, Library of Congress.
Death Valley, California. Death
Valley summer temperatures are over 120 degrees. Do you think an
egg would fry there? Photo from the Prints & Photographs Division, Library
View other unique ways to cook:
egg fried on the hood of a car. (Note:
Click through the slide show to get to the picture.)
egg fried on an XP computer.
cooked on a car's engine.
in the dishwasher.
cheese sandwiches cooked with a clothes iron.