By Peter de Kruijff, ABC

Perfection in the field of cooking an egg is a topic both subjective and controversial.

Perhaps you prefer a scramble over a hard-boil for your brekkie. Maybe you swear by a poach.

I prefer a soft-boil wrapped in a piece of bread – AKA the exploding egg sandwich – but getting both the egg yolk and white cooked to perfection can be tricky with overcooked yolks or undercooked whites the main problem.

The pursuit of eggy excellence – the optimal texture and flavour for yolk and egg-whites combined – can became an obsession, one that even scientists will wade into.

In research published today, a team of Italian scientists claim to have developed a new technique they think creates the perfect cook and texture for an egg that’s still in its shell, while maintaining a higher nutritional value than other methods.

To cook a periodic egg you go back and forth between boiling water and a bowl of water at 30C in two minute intervals.
Photo: Supplied: Foam Lab

The process, outlined in the peer-reviewed journal Communications Engineering and dubbed the “periodic egg”, involves cycling an egg, weighing 63 to 73 grams, every two minutes from boiling water to a bowl of tepid water, about 30 degrees Celsius, for 32 minutes total.

To discover this method, the team, from the University of Naples and Italy’s Institute of Polymers, had to solve the biggest problem that comes with cooking eggs: that yolk and whites cook at different temperatures.

Bridging the temperature gap

The problem, according to lead author Emilia Di Lorenzo, a materials and food scientist from the university’s Foam Lab, is that the optimal temperature for cooking whites is 85C while for the yolk it’s 65C.

“The cooking of an egg is basically a problem of energy transfer,” she said.

In other words, how do you control the temperature for two different materials inside a single object to get the perfect cook?

Lead author Emilia Di Lorenzo isn’t actually a fan of eggs.
Photo: Supplied: Foam Lab

There are existing methods that come close.

In Japan the onsen tomago (hot spring egg) is boiled in-shell, between 63C and 70C, for creamy whites and yolks.

The restaurant scene in the western world blew up in 2002 when French physical chemist Hervé This came up with the 65-degree egg (or 6X egg for experimentation with other close temperatures).

This uses an oven or sous vide method, where an egg is placed in a vacuum-sealed food bag then slow-cooked in 65C water, resulting in both white and egg having a custard-like consistency.

In both onsen and sous vide 65C processes, the egg white doesn’t fully set since not all its proteins reaches a high enough temperature to coagulate, so often cooks will drain off the translucent uncooked parts.

Ernesto Di Maio, Foam Lab’s director and a study co-author, says some chefs try to get a harder set on the whites by breaking the egg and cooking its two parts separately, creating fancy meals he has seen go for €80 ($123)

Over a beer with a colleague he wondered if they could transfer their experience as material scientists working in foam structures and polymers, to solve the problem.

“I have been working for some years on a way to give materials different properties in the same object,” he said.

“Be it a wing of an airplane or bone for substituting tissues.”

Ms Di Lorenzo said the team modelled thermal profiles to understand the temperature changes needed to perfectly cook both the yolk and white of the egg.

Their calculations showed the egg needed to go through periods of being in both hot and cold water so the white experiences temperatures between 37 and 100 degrees, while the yolk stays at 67 degrees for the whole cook.

Ms Di Lorenzo said there was an additional surprise on testing the nutritional value of periodic egg yolks compared to hard-boiled, soft-boiled and the 6X method.

She said the amount of polyphenols, a micronutrient with health benefits, was noticeably higher than other egg cooking techniques.

Further research is needed to find out why this happens, although Dr Di Lorenzo thinks it might be because the periodic egg is cooked at the exact temperatures that proteins in whites and yolks start to break down.

Dr This, who works at France’s National Institute of Agricultural Research and was not involved in the study, said the cooking method described was fun but had been done before.

“[Periodic cooking] was proposed about one century ago for meat, alternatively put in hot and cold water,” he said, adding he had previously tried the technique with “no sensory advantages”.

He was also surprised the study authors did not consider microwave cooking or pascalisation (sterilising food under high pressure) as comparisons.

How does it taste?

The periodic egg ultimately has whites similar to soft-boiled and a yolk that’s similar to the 6X, which can take an hour to cook, the study claims.

As part of the study a panel of independent tasters compared periodic eggs with 6X and more conventionally boiled eggs.

They found:

• Hard-boiled eggs were less wet, more adhesive and powdery compared to periodic eggs. The whites were sweeter, but the yolk less sweet and without as much umami.
• Soft-boiled eggs had a shinier surface on their whites but were drier in the mouth and less sweet compared to periodic eggs. And the yolk was wetter, less sweet and not as salty.
• 6X eggs were much shinier and more transparent than periodic eggs, with a more soluble taste. But the yolks were similar.

A food sensory analysis of egg characteristics. Red: hard boiled; yellow: soft boiled; green: sous vide; and blue: periodic.
Photo: Supplied: Communication Engineering

But Dr This said the study only used one type of hard-boiled egg, which can be cooked to different extents, and one temperature of 6X egg was also raised as a concern.

It only mentioned a sous vide 6X method and did not take into account ovens and even a dishwasher could be used instead, he added.

As to what the authors think of their creation, Ms Di Lorenzo, who will be awarded a doctorate later this month for a thesis on cooking yeast-less pizza dough, doesn’t actually like eggs that much.

Dr Di Maio, however, thought the result was amazing.

I also had a crack at cooking a periodic egg, and the yolk texture was not quite like anything I’d had before from out of a chicken.

It’s a bizarre sensation to munch on a creamy yolk inside firm boiled whites when comparer to past egg experiences.

I can see myself trying to perfect the method on a lazy Sunday, but with all the back in forth between pots, the soft boil sure seems a lot easier.

Dr Di Maio said playing around with timing and the non-boiling water temperature could also tweak the texture and flavour results.

In the meantime, he jokes he could start selling periodic eggs for €100 ($165).

But with the release of the paper, the experimentation is now in the hands of the public and hospitality scene.

And the hunt for the perfectly cooked egg continues.

– ABC