The Perfect Hard Boiled Egg

With Easter only a week away, it seems like the perfect time to talk about the steps to a perfect hard boiled egg. Kitchen lore is FILLED with different techniques to hard boiling an egg. But which one is accurate. The quick answer is use a candy thermometer and keep the water between 180 and 185 F for 25 minutes. However, if you’re interested in the overall experiment, read on!

The objective in the experiment is to create a perfect egg that is easy to reproduce in any kitchen. With that in mind, we ruled out the “Bring to a boil and then cover and let sit for 15 minutes off heat” method. Due to the differing boiling points as elevation changes, the initial temperature would vary greatly. In addition the amount of water in the pan, the material the pan is made out of, and the temperature of the eggs when they went into the water will have a huge impact on each time the egg is boiled. So it’s impossible to get a consistent egg using this method.

In order to make things translatable across multiple kitchens, it seems most appropriate to cook at a specific temperature for a specific time and compare the results of the egg. This way ANYONE can recreate it at home.

I chose 3 temperatures: 160 F, 185 F, and 203 F (boiling point at my elevation).

-The goal of creating the perfect egg is:
-Tender, easily peel-able egg white
-Minimal egg white loss due to peel stick
-Mild smell, with very minimal sulfur scent.
-Cooked yolk with smooth texture
-Minimal gray ring around the outside of the yolk

Let’s talk about the chemistry of an egg to give a little background on our little experiment.

The egg white is made up of 4 layers of white, alternating between thin and thick whites. (In fact the only difference between a Grade AA and Grade A egg is the ratio of of thick egg white to thin egg white. The egg white starts to thicken up around 145 degrees, and sets solid at approximately 160.

Egg yolks are approximately 14% protein… with small amounts of trace elements like iron. They thicken at approximately 160 degrees and really setup around 170.

The testing:

In all tests the egg was added to cold water and then brought to temperature. Timing started from the moment the target temperature was reached. All the eggs were cooked in a uniform amount of water, but time and temp were varied based on the demands of the test. At the end of the time, each egg was immediately removed from the hot water and placed into a cold water bath for 5 minutes to slow the formation of Hydrogen Sulfide (the compound which in small amounts gives a pleasing egg smell, but in larger amounts creates a rotten egg smell). The egg was then allowed to rest at room temperature.

I used eggs that were over days old, as the pH of egg whites change over time making them less susceptible to peel stick as they age. The fresher the egg, the more likely the peel will stick.

For the first test, I opted for a standard boil, which at my elevation is approximately 204 F.

Although the egg at 8 minutes was completely cooked with no visible gray ring around the yolk, there was a medium egg smell and the egg white’s texture was slightly rubbery – not quite the texture we wanted.

Every food scientist worth his salt knows that egg whites start to thicken at 145 and egg yolks thicken at 160. So why not cook an egg at 160 for an extended period of time and see how it worked out?

It was surprising to see that even after 45 minutes at 160 F, the egg white was EXTREMELY tender, with no egg smell. However, the white was so tender that a large portion of the egg white ended up staying with the egg shell. Delicious taste, but an unappealing look.

At 185 degrees, the hands down winner was 25 minutes. The egg white was soft and tender, no egg stuck to the peel, the egg smell was mild and pleasing, and the yolk had a very minor gray ring. Not quite perfect, but better than the other eggs so far.

Which brought us to the next challenge. How would the egg differ if it were cooked in an apparatus with much more control over temperature. I set the Sous Vide Supreme to 185 and started testing. In this scenario the egg at 25 minutes was PERFECT. The white was tender, no egg stuck to the peel, the egg smell was mild and the yolk had no gray ring? What changed?

When I went back and reviewed the notes from the first experiment at 185, the temperature got as high as 190 degrees at a couple of points in the experiment. So, I recreated the 185 stove top test taking great care to keep the temperature no higher than 185, but allowing for some temperature drop, as low as 175 F. It worked. The gray ring was gone!

Final recommendation? Buy your eggs at least 3 days before you plan to cook them. Start your eggs in cold water. Use a thermometer and keep the temperature of the egg between 175 and 185 for 25 minutes and then immediately immerse your eggs into cold water. You will be rewarded with a deliciously perfect hard boiled egg.

Happy Easter.

2 comments to The Perfect Hard Boiled Egg

  • Anita

    so a rolling boil is too hot? My last boiled eggs were cooked for about 25 min up at a boil.
    The shell stuck, but the eggs didn’t have the grey ring though or a stink. they tasted fine, just ugly. had to make egg salad, not good for deviled eggs.

  • admin

    You are correct that a rolling boil is too hot, as it tends to cause the ugly gray ring around the yolk.

    In your case the likely suspect that caused the sticky shell was either from using eggs that were too fresh, or not immediately soaking them in cold water after taking them off the stove.

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