When making hard-boiled eggs, it is important to use the same size eggs, as their cooking times differ. If using farm eggs, or eggs purchased from a farmers market, use an egg grading scale to determine the grade of your egg.
If you are planning to hard-boil farm fresh eggs think ahead. Eggs that are too fresh will be almost impossible to peel, so refrigerate them for about a week before hard-boiling. According to the American Egg Board, eggs need a “breather,” allowing the eggs “time to take in air, which helps separate the membranes from the shell.”
Place eggs in a saucepot large enough to hold them in a single layer. Add water to the pot so they are covered by at least one inch. Bring water to a boil, then turn off heat. Cover pot and allow to sit for 9 minutes for medium eggs, 12 minutes for large eggs and 15 minutes for extra-large eggs.
While eggs are sitting in the saucepot, fill a bowl with iced water. Drain eggs and crack the wide end of the shell, with a spoon. Immediately quick-chill eggs by submerging them into the prepared bowl of ice water. Beginning at wide end, peel eggs. If you are having difficulty, peel eggs under cool running water.
While hard-boiled eggs with a greenish-gray ring around the yolks are not terribly attractive, it’s not an indication that your eggs are bad, and it won’t affect their taste. Discoloration occurs as result of sulfur and iron compounds in the egg reacting at the surface of the yolk. It may be minimized by not cooking eggs at too high a temperature, or for too long a time and by quick-chilling the eggs immediately after they are cooked.
If you live in an area where you’ve got a high amount of iron in your water, your eggs may develop a greenish ring around the yolks, as well.