Why does pressure cooking of chicken eggs make eggs easier to peel?

Question

In an experiment, I cooked a 12 organic chicken eggs from the same batch:

A) 6 in boiling water and

B) 6 in a pressure cooker:

• 6 eggs in a basket which is on a tripod inside the cooker
• 5 minutes in hot steam at 117 °C
• waited 5 minutes to cool down until the pressure was at room level
• alternatively I cooled the cooker with cold water from outside until the pressure was gone.

In both experiments the eggs were put in the cold cooker without a hole in the shell. The eggs were put in a bowl with cold water in the end.

I found that the shell and membrane of the pressure-cooked eggs were a lot easier to remove. (The eggs also seemed to taste fresher and more intense.) I could not find a reason or explanation. I have repeated this since 2016 once a week.

The effect is remarkable, because organic eggs are often much more difficult to peel than factory farming eggs.

Is there an explanation for the pressure-cooked eggs being easier to peel?

I would like to see reliable sources (e.g. papers or other trustworthy publications), not just personal opinions.

Answer 1

Yes, I wrote a post about this a few years ago - the first to describe the method in a home pressure cooker. The theory goes that the pressure difference inside and outside the egg PLUS the shock of the cold facilitates the detachment of membrane from the shell. The Kitchn tried and confirmed my method and many of my readers will no longer hard boil an egg any other way but Serious Eats had different results - I don't know why.