Nothing is 100% but here are some tricks to get the shells to come off clean. These tricks almost always work for me except when I don't cook the eggs long enough.
Put enough cold tap water into the pot to cover the eggs. Put the eggs in when convenient, before or after putting the pot on the stove. I don't boil the water first or cover the pot (you can cover if the stove doesn't get very hot).
Add a lot of salt, like a couple of teaspoons for half a dozen eggs. The salt makes the water boil hotter. Add a couple tablespoons of vinegar to the cooking water. This softens the shells slightly. I use white vinegar cause it's cheap but any vinegar will work. Note: I used to be allergic to vinegar but had no problems boiling my eggs with it; it doesn't seep through.
Another trick which I haven't used for years but my mom did, is to prick the egg with a pin before boiling. There is a special tool for this you can get for a dollar or so in a drugstore or supermarket with kitchen supply equipment. I like the kind that doubles as a refrigerator magnet. Put the flatter end of the egg into the depression and push until the pin goes through.
Cook for 20 minutes in a nice rolling boil. Don't simmer; the water should be boiling. Turn down the heat only to prevent boil-overs. You can cook for up to 30 minutes if you like. The idea is to get the eggs cooked enough so that the yolks are fully hard and the shells come off, but not so hard as to get a green ring between the yolks and the whites (it is safe to eat).
The final step is to cool the eggs in cold water. This can be done anytime. But the eggs will not peel well if they are warm. If you refrigerate the eggs you will need to warm them slightly before peeling.
(posted to rec.food.recipes 12/97)
