How to make a perfect hard-boiled egg

Your hard-boiled eggs are rubbery and the yolks have a yucky green edge. What are you doing wrong? If you’re like most people, you are cooking them too hard and too long. Easy does it with hard-boiled eggs.

Cooking times depend on factors that include the size of the egg, how many you are cooking at one time, whether they are cold or at room temperature, and whether you are near sea level or up in the mountains.

Bigger eggs take longer to cook than small ones, as do cold eggs and eggs boiled at high elevation. Because water boils at a lower temperature at higher elevations, you will have to boil your eggs longer than at sea level.

Freshness also influences the whites’ cooking time. Fresh eggs’ whites are cloudier than older eggs, due to the presence of carbon dioxide. As an egg ages, carbon dioxide is given off and the protein in the white loses firmness, becoming transparent and watery.

When this happens, the temperature at which the whites coagulate and become hard decreases from 150 F. to 140 F., so a fresh egg takes longer to cook than an older one.

When you boil an egg for too long, the interior can quickly reach 158 F. or higher. At that temperature, you’ve passed the point of coagulation and the amino acids in the whites begin to break down, releasing sulfur-containing compounds that include stinky hydrogen sulfide (the rotten egg smell).

The sulfurous compounds also react with the iron in the yolk, causing a grey-green film of ferrous sulfide to form on the surface of the yolk. It’s harmless but unappetizing.

So what’s the bottom line? At Sonoma County’s altitude, follow this formula and you’ll have a perfect single egg every time.

Place the egg cold from the fridge into a saucepan and cover it with cold water. Set the pan on a burner and turn the heat to high. When the water reaches a full boil, and not a second later, remove the pan from the heat and put on the lid.

Let it sit on the counter for exactly 12 minutes. The egg will continue to cook as the water cools. Then run cold water over the egg to stop the cooking. It will be perfect.

If you want to boil more than one egg at a time, increase the resting time on the counter after the eggs reach a boil. Let three eggs sit for 17 minutes, five eggs for 20 minutes. Cool them under running cold water. Even if the water cools completely, the interior of the eggs will be hot enough to continue cooking.

Don’t worry about the ease or difficulty of peeling eggs cooked by the cold water start method. Just peel as carefully as you can. Wouldn’t you rather have a perfectly cooked egg with a few pockmarks than a smooth but rubbery egg with a chalky, green-edged yolk?

Jeff Cox is a Kenwood-based food and garden writer. Reach him at jeffcox@sonic.net.