As a mostly stay-at-home dad responsible for all the meals in our household, I depend on a supply of boiled eggs in the refrigerator — ready to be added to soups, salads, stews, sandwiches, stir-fries and tacos — as an essential part of my planning.
Years ago, in an effort to answer a perennial question — what’s the best way to boil an egg? — I hatched a plan using the only method I know: lots and lots of testing.
It was a multidecade endeavor. The series of tests I conducted variously as a kitchen monkey at Cook’s Illustrated magazine, as recipe czar at the website Serious Eats and in researching my cookbook produced good data, but none of it felt definitive. Further home experimentations (there have been weeks when my wife, Adri, begged me to stop serving egg salad for dinner) have left unanswered questions and conflicting results.
Do older eggs really peel more easily? (The internet insists they do.) Can an ice bath prevent green yolks? Is there anything the Instant Pot can’t do better? I simply did not have enough data to say for certain.
With that in mind, for my first column on cooking and science for The New York Times, I decided to undertake my greatest egg-peeling experiment yet, and I have finally come up with some answers.
Ninety-six volunteers came through my restaurant, Wursthall, in San Mateo, Calif., in August to peel and taste more than 700 eggs, cooked with various methods, making this — as verified with a cursory search online — the largest-ever double-blind egg-boiling-and-peeling experiment in the history of the universe. (If anyone from Guinness is reading, I have pretty extensive documentation.)
The eggs were ranked and timed to determine ease of peeling, then examined for flaws large (whites that were ripped or torn) and small (whites that were lightly pitted). Peeled eggs were tasted in pre-portioned, unlabeled, single-bite samples. When visual differences between the eggs may have affected the tasters’ judgments, we blindfolded them.
For some experiments — such as a test to determine how much eggs from true pasture-raised hens differ from the eggs that come 15-dozen-in-a-crate at Costco — I administered a triangle test. (The taster is given three samples. One of them is different. Her job is to tell us which is different.)
All of these tests were administered double-blind, meaning that neither the subjects nor the test administrators knew which eggs were which. Using the results, I designed a few 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 crack on.
First, let me share my idea of a perfect boiled egg: It should be tender throughout, even when fully hard-boiled. The white should not be rubbery, nor the yolk chalky or green. And above all, it should peel easily. There are few frustrations greater than watching a chunky divot of egg white dislodge itself as you claw clumsily at the shell.
Here’s the real trick, and it confirms the data I’ve been collecting for years now: By far the most important factor in determining whether a boiled egg will peel cleanly or not is the temperature at which it starts cooking. Starting eggs in cold water causes egg-white proteins to coagulate slowly, bonding tightly to the inner membrane of the shell. The difference is night and day: Cold-water eggs show nearly nine times more large flaws and double the number of small flaws.
There are two stovetop cooking methods that allow preheating for a hot start, and produce eggs that are equally easy to peel: boiling and steaming.
But taste tests showed that steamed eggs were more tender than their boiled counterparts. This is because steam is gentler than boiling water, allowing eggs to cook through without any hint of rubberiness in the whites or chalkiness in the yolks. Steaming an egg may take a minute longer than boiling it, but you save that time and more during setup: Bringing an inch of water to a boil is much faster than bringing a whole pot of water to a boil.
After testing three of the more popular time and temperature combinations on the Instant Pot (i.e., a pressure cooker), I unfortunately can’t recommend using one. It’s not any faster or easier than steaming eggs; the eggs are no easier to peel; and the time it takes various models of pressure cooker to achieve cooking pressure (and thus start the countdown timer) can vary widely, which makes the method unreliable.
Moreover, blindfolded tasters confirmed that the whites were noticeably tougher (given the same internal yolk temperature). This makes sense, given the high cooking temperature achieved in a pressure cooker.
Also not recommended: the briefly popular technique of baking eggs in their shells in a muffin tin.
Some variables had little to no effect. Adding small amounts of vinegar, baking soda or salt to your water is pointless. None offer advantages for peeling, while at the extremes, vinegar and baking soda produce off-flavors and colors (ghostly blue egg whites!).
The only difference between fridge-cold eggs and room temperature eggs is that room temperature eggs will cook about a minute faster.
What about freshness? Through my neighbor’s connections with an underground cabal of backyard chicken owners, I wrangled over 100 eggs, from straight-from-the-oviduct to two days old, from backyard flocks across San Mateo. I compared them with supermarket eggs that were at least two weeks old. (Every carton of eggs sold in the United States is stamped with a three-digit number from 1 to 365, representing the day of the year they were packed.)
Turns out that age doesn’t make much of a difference either. Even eggs still warm from the hen’s body peeled just as easily as the most grizzled specimen. (Taste tests also showed that most folks could not tell the difference between backyard eggs and supermarket eggs, and those who could were split on which were better.)
Pricking the fat end of an egg with a pushpin doesn’t affect how easily an egg peels, but it can prevent thin-shelled eggs from cracking under the pressure of gas expansion during boiling. It will also reduce the large dimple you often find at the fat end of the cooked egg, caused by the impression of an air pocket located there.
Immediately dunking your cooked eggs in an ice bath will have a similar dimple-reducing effect, but it also makes them a little more difficult to peel. This result surprised me, as previous smaller-scale tests had suggested a slight advantage in peeling eggs that were iced; but when a mountain of new data doesn’t fit your previous hypothesis, you change your hypothesis.
An ice bath also did not help reduce the incidence of the sulfurous green patina around overcooked egg yolks — eggs are so small that there is negligible carry-over cooking. If the yolk is green, it would have been green ice bath or no.
Even with evidence, I don’t expect everyone to adopt the steaming technique, and that’s fine. If you’ve got a method that works for you, stick with it (even if it’s the 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 far more to cooking than the pure science of the craft. I’m not here to tell you how to cook or to try and change your 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 that information to change your everyday cooking, or perhaps just to volunteer unsolicited cooking tips to a perfectly capable brunch host, I hope you find something useful.
Recipe: Perfectly Peelable Steam-Boiled Eggs
J. Kenji López-Alt is the author of “The Food Lab: Better Home Cooking Through Science” and the culinary adviser for the website Serious Eats. He is also the chef and co-owner of the restaurant Wursthall in San Mateo, Calif. His new column, about science and home cooking, will appear monthly.
