(Lansing State Journal, November 13, 1991)
Question submitted by: H. Barre of East Lansing
There is actually a lot of science in cooking eggs. Eggs are a great example of nature's packaging. If you squeeze the ends of an egg between the palms of both hands, it won't break. This is why eggs are stored and sold with their ends pointing up or down, and not lying on their middles. (If you don' t want to take our word for this, try squeezing the middle of the egg between your palms. Do this over a sink.) One feature of the egg is an air sac at one end, which serves as a shock absorber to keep the developing chick from being disturbed by the outside vibrations. When you put an egg into boiling water, the air sac expands. If the sac expands only a little, the yolk and white will be pushed into the rest of the shell, and the result will be a hard-boiled egg with a flattened end. If the air sac expands too much, the shell will crack, releasing egg white into the water. To eliminate this possibility, prick the fat end of the egg with a sharp pin to make a very small hole before placing the egg in water. If you don't trust yourself to prick the egg without breaking it, place the eggs in cold water and then bring the whole pot to a boil. This gives the air time to slowly seep out of the egg.
What happens if-despite your best efforts- the egg cracks anyways? Don't start over-just add a bit of vinegar or salt to the water. The vinegar or salt starts a chemical reaction which causes the egg whites to coagulate (thicken) and cook faster, preventing the white from streaming out of the egg. This is why good chefs poach egg in an vinegared water; the acid in the vinegar helps cook the whites faster, so that the poached eggs come in compact little balls. The piece of pineapple or orange served with poached eggs is not just for dressing up the plate-it's to help mask the slightly acidic taste from the poaching water.
If your hard-boiled egg yolks are coming out green, science has a solution for that, too. As an egg cooks, the proteins contained in the whites break down, releasing a sulfide gas. The gas moves toward the coolest part of the egg-the center- where the yolk is. Iron in the yolk interacts with the sulfide fas to produce the greenish tinge on the surface of the yolk. This can be avoided by not overcooking the eggs and rinsing them in cool water to stop the cooking process after you have removed them from the heat.
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