How to make ‘perfect’ hard-boiled eggs: Scientists say they cracked the code

The different egg-boiling techniques are seen (from left): hard boiled, soft boiled, sous vide, periodic. (Ernesto Di Maio via CNN Newsource)

If you think you have your egg-boiling technique down to a science, there is still a chance you haven’t prepared the “perfect” boiled egg.

Boiling an egg flawlessly is challenging because the albumen — or egg white — and the yolk have different compositions, requiring them to be cooked at varying temperatures to achieve ideal taste and consistency.

But now, scientists say they have officially cracked the code with a technique known as periodic cooking. This new method involves alternating the eggs between hot and lukewarm water cycles to optimally cook the albumen and yolk simultaneously without separating them, according to a new study published February 6 in the journal Communications Engineering.

Not only does periodic cooking produce the ideal texture and flavor for both the albumen and yolk, but it also helps the egg retain the greatest amount of nutrients with proven health benefits compared with other popular methods such as hard-boiling or sous vide, the study authors wrote.

“As a chef, this method makes perfect sense,” Micah Siva, a San Francisco-based registered dietitian and recipe writer who was not involved in the study, said via email. “People often forget that cooking is incredibly scientific … and adjusting cooking temperature to the properties and structures of the proteins within the egg can improve the quality.”

The best part? You don’t have to imagine it — you can try periodic cooking at home. Dr. Ernesto Di Maio, the study’s lead author, noted the experiment wasn’t conducted using fancy lab equipment but rather in his home kitchen. All you need is 32 minutes and a bit of patience.

Cooking process for the perfect boiled egg

To cook the ultimate boiled egg, the researchers could have relied on trial and error, testing hundreds of eggs, said Di Maio, program manager of the bachelor and master’s materials engineering program at Italy’s University of Naples Federico II.

Instead, the team developed mathematical models and simulations to predict how heat transfers through the egg, which helped them identify the ideal cooking conditions for both the albumen and yolk. With these tools, Di Maio and his colleagues input factors such as water temperature and density to help them decide the time increments to switch the eggs between hot and lukewarm water, he said.

To test periodic cooking, the team filled a kitchen pot with tap water and heated it to the desired temperature on the stovetop. The researchers placed a food thermometer in both the hot and lukewarm water to ensure consistent temperatures throughout the cooking process.

The team then cooked fresh, shell-on hen eggs using four methods: hard-boiling, soft-boiling, sous vide and the new periodic cooking technique. In total, Di Maio and his colleagues prepared 160 eggs, using 40 eggs per cooking method.

The traditional methods served as control samples to compare temperature profiles, texture and nutrient retention.

Hard-boiled eggs were cooked for 12 minutes, soft-boiled ones for six minutes and sous vide eggs were prepared at 65 degrees Celsius (149 degrees Fahrenheit) for one hour.

For the periodic method, scientists alternated submerging the eggs for two minutes in boiling water at 100 C (212 F) and lukewarm water at 30 C (86 F). This cycle was repeated eight times for 32 minutes.

While the traditional methods resulted in consistently increasing internal temperatures throughout the egg, the periodic method maintained a constant yolk temperature of 67 C (152.6 F), with the albumen reaching temperatures ranging from 87 C to 100 C (188.6 F to 212 F) in hot water and 30 C to 55 C (86 F to 131 F) in lukewarm water.

This dynamic heat distribution allows both the albumen and yolk to achieve their ideal textures and consistency, according to Di Maio.

While Siva noted periodic cooking is an interesting concept, she said she wouldn’t take the time to cook an egg for 32 minutes.

“Most people struggle to get a meal on the table and are looking for shortcuts … not a way to fuss over something as simple as a boiling egg,” she said.

Comparing the techniques

While the researchers were able to visualize some of the differences between the eggs, they also performed a texture profile analysis and sensory analysis to measure various properties, including consistency, color, texture and taste.

Sensory analysis, which involves texture and taste, is objective but provides detailed insights into the elements people can expect when trying periodic cooking.

Overall, the albumen of the periodically cooked eggs had a texture most similar to soft-boiled eggs, whereas the yolk closely resembled sous vide-cooked eggs, the researchers noted.

Di Maio described the yolk of the periodically cooked eggs as an excellent balance between solid and liquid, with a jelly-like consistency, while the albumen was well-set without being too firm or transparent.

He shared some of the periodically cooked eggs with friends and family.

He said they were amazed by the contrast of the textures of the albumen and yolk, something not easily achieved with traditional methods.

If you decide to give periodic cooking a try at home, be forewarned that consuming raw or undercooked eggs may increase your risk of foodborne illness, especially if you have a weakened immune system or have certain medical conditions.

Researchers were also interested in exploring the protein denaturation — the changing of physical and chemical properties — to assess the levels of polyphenols and amino acids within the yolk, as these contain vital nutrients.

Interestingly, compared with other methods, periodic cooking preserved the highest levels of polyphenols, chemical compounds that help prevent cell damage.

Foods rich in polyphenols have anti-inflammatory and antioxidant properties, which have been shown to help protect against several diseases and may reduce the occurrence of prostate and breast cancer, according to the study.

Siva noted that the nutrient composition changes with the periodic method are minimal, but eggs are still a great source of protein and healthy fats no matter the cooking form.