Bill's Comments

Why am I writing about this? After all, it’s simple, put the eggs in water, boil them a while, cool them, and peel them. Then why are the yolks green sometimes and why don’t they always peel? Huh? I take boiled eggs everyday for my breakfast, so I really care about this problem. In my usual obsessive way I have figured out how to get consistent boiled eggs by reading and experimenting. If you are happy with your boiled eggs, skip to another post, this may be boring (It will certainly be more than you ever wanted to know about it.). If not, then read on.

Boiling eggs IS simple, once you understand the details. First of all, very fresh eggs are bad candidates for boiling. They are almost impossible to peel. Second of all, boiled eggs don’t spoil in the refrigerator as far as bacteria, but after several days the yolks start turning green (You actually can keep boiled eggs at room temperature for several days, but they start turning green fast, and the taste goes downhill. They are still safe. This knowledge is the product of a month of living in a cold-water room with no refrigerator.). The main key is in the boiling process itself. If you are in a hurry, you are guaranteed to have a problem with your boiled eggs. Properly boiling eggs takes at least 25-30 minutes. You’re better off frying or scrambling them if you don’t have time.

To understand why certain things must be done, we need to know something about the structure of eggs.[1] The important parts to us are the iron in the yolk, the sulfur in the whites, the membrane between the white and the shell, and the air pocket. The shell itself is important only in that it may have hidden cracks or weak spots.

Green yolks come from the combining of the iron in the yolk (of which there is a lot) and sulfur which comes from the breakdown of sulfur-containing amino acids in the protein of the yolk. Proteins in the white break down after excessive cooking or long storage. So that is why you don’t want to over cook them or store them too long. It is also why you want to cool eggs rapidly. The cold temperature on the outside of the shell draws the sulfur of the protein away from the yolk which is hotter. When the sulfur is released from the white, it forms hydrogen sulfide, a gas which is the smell of rotten eggs. The cold water on the shell causes the gas to migrate with the temperature gradient to the outside.

The membrane between the shell and the yolk is the key to peeling the egg. When eggs cook the protein of the white coagulates and wants to shrink. If eggs are very fresh, they contain enough water in them that the white cannot shrink, and it remains so close to the membrane that it sticks. After a few days, eggs lose some water through the shell which is porous, and when the white cooks, it shrinks, pulling away from the membrane. If the egg is tightly held in the pan while boiling, the part of the shell that touches the pan will be hotter, and it will also be the lowest point inside the shell. This does not allow the white to shrink away from the membrane, so that even if everything else is right, the white will stick at that point when peeling.

The air pocket is an aid to peeling. It is usually on the large end, though I often see it on the side of the egg when peeling. It gives a place where the shell is already pulled away from the white, so that when the egg is cracked and you start to peel, you have an easy entry to the process. The membrane is actually a double membrane, and it is at the air pocket you can see this. The pieces of shell will be stuck to the membrane like safety glass to its center membrane, but there will be a membrane on the white at the bottom of the pocket.

When peeling the egg, if your hands are wet or you hold the egg under a small stream of water, it will peel easier. It is like lubricating something; the water eases the separation of the membrane and the white. Once you are aware of the membrane, you can see where it does and does not come off. Where it is still present, the egg will have a dull look and not be slippery. Gentle rubbing with a wet thumb or finger will usually roll it up and off the white. Getting your thumb between the white and the membrane is the key to rapidly and easily peeling the egg. You will know it is happening if the shards of egg shell stay together as you are peeling.

So now that you know more than you wanted to about eggs, what is the best way to boil them?

Fill a pan with cold water high enough to cover the eggs completely. Make sure the eggs have some room to roll around a bit in the pan. Place the eggs gently into the pan, and place it on high heat to bring it to a boil. Start with cold water so that the air in the egg has time to escape while expanding. This prevents forcing the white through the cracks in the egg or opening a weak spot that allows the white to escape.

Once the eggs come to a boil, turn the heat down and simmer for 13-15 minutes. They will cook no faster boiling than simmering, the water temperature is the same. Simmering prevents overheating one particular spot on the egg. The time is important because we need to cook the white enough to properly congeal, but not enough to start breaking down. Less then 13 minutes can produce a slightly orange yolk which is less dry, but can cause the eggs not to peel properly (The whites are not completely shrunk.), and over 15 minutes will cause green yolks.

Once the cooking time is up, the eggs must be rapidly chilled. The main purpose of the speed is to prevent green yolks. The chilling is necessary to peel them cleanly. Remove the eggs from the stove and gently pour off the hot water in the sink, and cover with cold water. Drain this water, and cover again just barely. Now add as much ice as you can to the pan. Either fill the pan or use up your available ice. If you have an ice maker you are in good shape. Otherwise, remove the cubes from the trays ahead of time and store in a bowl to add quickly. The eggs must cool for a minimum of five minutes and ten is better. The chilling firms the yolk and causes it to shrink further from the membrane. Also during cooling the condensation of the steam in the air pocket will create a partial vacuum in the egg that will draw in water to lubricate the separation of the membrane from the white. This is why ten minutes is better. The water is drawn in slowly.

To help peeling, you can gently shake the pan of eggs to crack them before adding the cold water. However, if the cracking deforms the egg shells, when the whites cool, they will be permanently deformed. Not a problem for cooking with the hard-boiled eggs, but may ruin their appearance for deviled eggs and canapés.

To peel the eggs, sharply rap the large end against the side of the sink to create an area of shattered shell. You can pinch this up to make an opening into the shell for peeling. I do not crack the entire egg. I have found that by pushing with my thumb away from me, I will usually remove larger pieces of shell at a time, and they will stay together better. As mentioned above, a wet hand and/or a small stream of water will ease the process. Once the egg is peeled, make sure all the little fragments of shell are removed (They can be as fine as sand.). A quick rinse will do this.

If you have done it correctly, the hard-boiled egg will have a firm but still slightly soft textured white and the yolk will be perfectly yellow with no green. The taste will be light and not overly “eggy”.

Some updates:

I have tried a suggestion from a professional chef--put the eggs in water and bring them to a boil, then set the pan off the heat and let them set for about half an hour. When I tried it, I got green yolks.

Put about 1-2 Tablespoons of salt in the water. If an egg is cracked, this prevents the white from running out, because it denatures the surface of the white to solid protein, sealing the egg.

[1] Nutritionally eggs are one of the most concentrated sources of good stuff you can eat – high protein, high iron, and high lecithin, which is used to make acetyl-choline, the main neurotransmitter in the brain. The cholesterol has given eggs a bad rap. The amounts are many times less than your body manufactures daily, and is of concern only to those with very high cholesterol in the blood. It is not even in a form to be readily used by the body.