As a daddy who is mostly at home and responsible for all meals in the household, I rely on a supply of boiled eggs in the fridge – ready to be added to soups, salads, casseroles, sandwiches, stir and fries tacos – as an essential part of my planning.
Years ago, in an attempt to answer a perennial question – what is the best way to cook an egg? – I hatched a plan using the only method I know: lots and lots of testing.
It was a multi-decade endeavor. The series of tests I conducted in various ways such as a kitchen cup in Cook's Illustrated magazine, as a recipe czar on the Serious Eats website and in researching my cookbook gave good data, but none of them felt definitive. Further home attempts (there have been weeks where my wife, Adri, asked me to stop serving egg salad for dinner) have left unanswered questions and conflicting results.
With that in mind, I decided on the first column about cooking and science for The New York Times, to conduct my biggest eggshell experiment yet, and I've finally come up with some answers.
Ninety-six volunteers came through my restaurant, Wursthall, in San Mateo, California, in August to peel and taste more than 700 eggs, prepared using various methods, which did this – as confirmed by a cursory search online – the largest ever double-blind egg-boiling and peeling experiment in the history of the universe. (If anyone from Guinness reads, I have quite extensive documentation.)
The eggs were ranked and timed to determine simple peel, then examined for large errors (whites that were ripped or torn) and small (whites that were easily pitted). . Peeled eggs were tasted in pre-portioned, unlabelled juniper samples. When visual differences between the eggs may have affected the tasters' judgments, we have blindfolds.
For some experiments – for example, a test to determine how many eggs from true grazing chickens differ from the eggs that come 15 dozen in a box at Costco – I administered a triangle test. (The tastemaker gets three samples. One of them is different. Her job is to tell us what's different.)
All of these tests were administered double-blind, meaning that neither the test subjects nor the test administrators knew which eggs were which. Using the results, I designed some subsequent experiments for another day of testing before drawing conclusions.
I have bad news: There is no way to guarantee eggs that peel 100 percent of the time. But if 87 percent or higher is a number you can work with, let's turn on.
Let me first my idea of a perfectly cooked egg: It should be tender throughout, even when completely hard-boiled. The white should not be rubbery, nor the egg yolk chalk or green. And above all, it should flake easily. There are few frustrations greater than watching a thick divot with egg white loosen itself when itching clumsy on the shell.
Here is the real trick, and it confirms the data I have been collecting for many years now: By far the most important factor in deciding whether or not to boil a boiled egg is the temperature it starts to boil. Starting eggs in cold water causes egg white proteins to coagulate slowly, and binds tightly to the inner membrane of the shell. The difference is night and day: Cold water eggs show almost nine times more large defects and double the number of small faults.
There are two cooking methods that cook up that allow a hot start to be preheated, and produce eggs that are just as easy to peel: boil and steam.
But taste tests showed that steamed eggs were more tender than their cooked counterparts. This is because steam is milder than boiling water, so eggs can boil through without any hint of rubberiness in whites or chalk in the egg yolks. Steaming an egg can take a minute longer than boiling it, but you save time and more during setup: Boiling an inch of water to boil is much faster than boiling an entire pot of water.
After testing three of the more popular time and temperature combinations on the Instant Pot (ie a pressure cooker), I unfortunately do not recommend using one. It is no faster or easier than steaming eggs; the eggs are not easier to peel; and the time it takes different models of pressure cooker to obtain the cooking pressure (and thus start the countdown timer) can vary widely, making the method unreliable.
In addition, blindness to the eyes confirmed that the whites were noticeably tougher (given the same internal egg yolk temperature). This makes sense given the high boiling temperature achieved in a pressure cooker.
Also not recommended: the briefly popular technique for baking eggs in the shells in a muffin tin.
Some variables had little or no effect. Adding small amounts of vinegar, baking soda or salt to your water is pointless. No one benefits from peeling, while the extremes, vinegar and baking soda produce flavors and colors (ghostly blue egg white!).
The only difference between refrigerated eggs and cold eggs is that room-temperature eggs will cook about a minute faster.
What about freshness? Through the neighbor's connections with an underground cabal of chicken owners in the garden, I quarreled over 100 eggs, ranging from straight from two to two days old, from flocks in the backyard over San Mateo. I compared them to supermarket eggs that were at least two weeks old. (Each carton of eggs sold in the United States is stamped with a three-digit number from 1 to 365, which represents the day of the year they were packed.)
Shows that age does not make much difference either. Even eggs that are still warm from the hen's body peel as easily as the most gripped specimen. (Taste tests also showed that most could not tell the difference between garden eggs and supermarket eggs, and that they could be split on which ones were better.)
Stabbing the fat end of an egg with a needle stick does not affect how easily an egg peels , but it can prevent thin-skinned eggs from cracking under the pressure of gas expansion during boiling. It will also reduce the large cavern you often find at the fat end of the boiled egg, caused by the impression of an air pocket lying there.
Immediate dunking of the boiled eggs in an ice bath will have a similar coarsening effect. , but it also makes them a little harder to peel. This result surprised me, since previous tests on a smaller scale had suggested a slight advantage in peeling eggs that were ice; but when a mountain of new data doesn't fit your previous hypothesis, you change the hypothesis.
An ice bath also did not help reduce the occurrence of the sulfur-green patina around overcooked egg yolks – eggs are so small that there is insignificant cooking. If the egg yolk is green, it would have been a green ice bath or no.
Even with proof, I don't expect everyone to apply the steaming technique, and that's good. If you have a method that works for you, stick to it (even if it's Instant Pot).
Science can deepen your understanding of the interaction between heat and molecules, between taste and pleasure. It can undoubtedly make you a better cook. But there is much more to cooking than the pure science of craft. I'm not here to tell you how to cook or try to change traditions and habits; my only job is to show you the data, demonstrate the science and deliver a tasty recipe or two.
Whether you use this information to change your everyday cooking, or maybe just to volunteer unwanted cooking tips into a perfectly skilled brownie, I hope you find something useful.
J. Kenji López-Alt is the author of "The Food Lab: Better Home Cooking Through Science" and the culinary advisor for the website Serious Eats. He is also a chef and co-owner of the Wursthall Restaurant in San Mateo, California. His new column, on science and home cooking, will appear monthly.