The Secret to a Perfectly Cooked Egg

How long should you boil your breakfast egg? BBC Good Food suggests it's between five to 10 mins: five for set white and runny yolk, 10 for the classic hard boiled. UK's Egg Info recommends three to eight mins for the same results. But a team of Italian researchers beg to differ. In their recently published paper “Periodic cooking of eggs” (Communications Journal, Feb 2025), coauthors Pellegrino Musto, Ernesto di Maio, and others propose a whopping 32 mins. 

Maio says, “The inspiration came from a stimulating discussion with one of our colleagues at University of Naples Federico II, where we learned that some high-level chefs cook eggs by separating the yolk and albumen and preparing them at their respective optimal temperatures (65°C for yolk and 85°C for albumen) to achieve their ideal textures. As materials scientists who work daily with structuring materials, the challenge seemed obvious: what if we could cook both egg phases at their optimal temperatures without cracking the shell open?”

Egg White and Yolk: An Imperfect Combo

The dilemma in egg cooking, the researchers point out, is the combination of albumen (egg white) and yolk. “Due to the fact that albumen and yolk have two very different compositions, they require two different temperatures for optimal cooking, namely around 85 °C for albumen and around 65 °C for yolk.” 

True, you can cook them separately, but that would deprive you of the pleasure of cracking the boiled egg at the breakfast table with the tip of your spoon. So the researchers come up with a temperature-alternated cooking method that let you keep the shell intact.

“We explore the idea of imposing two different cooking temperatures in two different regions of the egg without necessarily cracking the shell open. The inspiration comes from previous works of our group, where time-varying boundary conditions (BCs) in the mass transport of the blowing agent are exploited to produce foams with different layers in terms of morphology and/or density,” according to the researchers. 

In practical terms, that means “to place the raw shell-on egg alternatively in hot water and cold water for relatively short periods of time and repeat these cycles until the cooking of both the yolk and the albumen is reached.”

The researchers reveal they employed mathematical modeling of “concomitant heat transfer inside the egg and gelation of both egg yolk and albumen,” along with Computational Fluid Dynamics (CFD) simulation. They compared four different methods: hard-boiled, soft-boiled, sous vide (vacuum-sealed); and periodic—their own method. 

For validation and testing, the researchers relied on sensory perfection—eating the cooked eggs: “The [periodic cooking] method not only optimizes egg texture and nutrients, but also holds promise for innovative culinary applications and materials treatment,” they note.

A Taste of Science

The prescribed periodic method is to place the egg “alternatively in boiling water (100 °C) for 2 min and water at 30 °C for 2 min, for a total cooking time of 32 minutes, which corresponds to the repetition of the hot and cold cycles for a total of 8 times.”

The notes from the researchers' sensory analysis evaluation read, in part, “Compared to the periodic, both the albumen and yolk of the hard boiled sample differ mainly for its less wet, more adhesive and more powdery/sandy consistency when pressed between tongue and palate. When analyzing the taste, the egg albumen is sweeter and more stringent, the yolk is less sweet and both egg albumen and yolk have less umami taste (although it is perceived at a weak intensity) ... In conclusion, the periodic egg is more similar to the soft boiled when analyzing the texture of its albumen, while it is very similar to the sous vide sample when considering its yolk.”

Maio admits the periodic method takes longer than traditional methods, so it should be reserved for special occasions. He recalls, “I often prepare eggs for my family and friends. Last Easter, I cooked 15 periodic eggs for my family.”

A few years ago, Maoi and his colleagues also conducted a study on pizza foaming (dough leavening), which reveals insights into bubble dissolution that happens as a consequence high-pressure application.