Rubbery

The chefs know there’s plenty that can go wrong when cooking an egg that should have a soft yolk surrounded by firm whites. “The egg white shouldn’t be slimy or rubbery, and it should have an even texture. The yolk must be creamy, not watery,” says Hagan, who is French. “It’s so difficult because the yolk and the white each have a different coagulation temperature.”

Freshness also affects cooking time. Mulders has brought ten white older eggs and ten brown fresh eggs. On the spot, students must cook one of each type to soft-boiled perfection. But before they begin the practicum, they may present their approach to the jury.

Caliper

Student Fieke Wijnen explains how she arrived at a cooking time of 380 seconds for each egg. “In theory, an older egg needs more time. But our older egg is slightly smaller — 5.7 cm by 4.6 cm — than the fresh one at 6.2 cm by 4.5 cm, so it might be done a bit earlier.” Wijnen and her teammate, Mike van den Boogaard, entered the dimensions and material properties into the program Comsol. “We assumed an oval egg with a circular yolk. We found the respective coagulation temperatures online.”

Cooling shock

After boiling, the eggshell should come off easily, and the chefs pay close attention to how well the egg peels. “You can improve this by adding a bit of salt to the cooking water,” Kersemaekers advises. “But more important is giving the egg a thermal shock under cold water once it’s done, so the cooking process stops. If you don’t ‘shock’ the egg properly, there’s a chance the membrane will stick to the white. That makes peeling unpleasant.”

She and Hagan are surprised that none of the students pierce a small hole in the raw eggs. “That relieves the pressure in the eggshell and reduces the chance of cracking. For a very fresh egg it’s not necessary, but for an older one I would always pierce the air chamber.” Cracks can also appear when the water boils too vigorously. “Then the egg bounces around in the pan. The ideal temperature is just below boiling. Cooking eggs should be gentle.”

When the chefs evaluate the eggs prepared by Wijnen and Van den Boogaard, Hagan inserts a thermometer. “While peeling, I thought it wasn’t done. Hmm, the yolk is at 50 degrees.” He slices the egg in half. “Beautiful, really beautiful. The separation between white and yolk is sharp. The yolk is creamy. Compliments.”

Homework

All students practiced at home — some longer than others. Viktor van Bilsen marinated eggs overnight. Teammate Jules van Gisteren explains why. “So far, we’ve mainly focused on heat transfer in different materials. But more factors influence flavor experience, hence Viktor’s marinade.” He thinks follow-up research is needed. “But just like with an egg, you should take this idea with a grain of salt,” he jokes.

Mulders sees the egg-cooking assignment as preparation for the second PEP project. “Students will then apply different physics disciplines interactively to solve a real-world problem from a company. Consider this a taste of consultancy experience.”