How to boil an egg Aug 27 2008
French cookery scientist Hervé This says that the 10-minute boiled egg is the wrong way to go about cooking your eggs. Temperature and not time is the governing factor to gloriously boiled eggs.
Recall that when an egg cooks, its proteins first unwind and then link to form a rigidifying mesh. But not all its proteins solidify at the same temperature. Ovotransferrin, the first of the egg-white proteins to uncoil, begins to set at around 61 degrees Celsius, or 142°F. Ovalbumin, the most abundant egg-white protein, coagulates at 184°F. Yolk proteins generally fall in between, with most starting to solidify when they approach 158°F. Thus, cooking an egg at 158°F or so should achieve both a firmed-up yolk and still-tender whites, since at that low temperature only some of the egg-white proteins will have coagulated.
"Cooking eggs is really a question of temperature, not time," says This. To make the point, he switches on a small oven, sets the thermostat at 65°C, or 149°F, takes four eggs straight from the box, and unceremoniously places them inside. "I use an oven in the lab; it's easier. But if the oven in your kitchen is not accurate, cook eggs in plenty of water, using a good thermometer." About an hour later -- timing isn't critical, and the eggs can stay in the oven for hours or even overnight -- he retrieves the first egg and carefully shells it. "The 65-degree egg!" he announces. The egg is unlike any I've eaten. The white is as delicately set and smooth as custard, and the yolk is still orange and soft.