Seemingly innocent events in our house often turn into science experiments.
Becki had made hard boiled eggs in her new pressure cooker. After they were done we figured out that the directions were unclear and the eggs should have been cooked on the low pressure setting (which also makes it lower heat).
The eggs were still edible. The only thing that was different was that the yokes were green on the outside. I have often seem hard boiled eggs where the yoke was green or gray on the outside, but this time it was very pronounced.
The kids asked why, and I had often wondered about that myself. So after a little research, we found the answer. When the eggs get hot, sulfur breaks off of one type of molecule in the egg white and combines with some hydrogen making hydrogen sulfide. Then when the hydrogen sulfide contacts the yoke, it reacts with the iron and makes ferric sulfide. The ferric sulfide is the green stuff. Don’t worry, it is okay to eat.
The article we read also said that the effect can be minimized by not overcooking the eggs and putting them in cold water as soon as they are done. Thus a science experiment was born.
I suggested to the kids that we make more eggs (at the correct pressure setting) and put some in cold water when they were done. Then we could cut them open and compare. We discussed the need to make some of the eggs normally (not putting them in water) so that we had a control for the experiment. Then the kids suggested that we put some in ice-water and some in hot water.
So we got our supplies and organized everything.
Elijah boiled the eggs.
All of the kids helped peel the eggs.
It is important to let the kids do as much of the experiment as possible so that they learn and enjoy science.
The egg in the ice water came out with a beautiful golden yellow yolk as we hypothesized. The egg from the cold water was the next best. But the egg from the hot water and the egg from the pressure cooker were not as green-gray was we expected.
We discussed why this was and concluded that it was probably because those eggs cracked while cooking. This may have allowed them to cool faster than they would have if the shells were intact.
So the experiment did not go perfectly, but that gave us a chance to talk about making sure that all factors in an experiment are controlled and how to design a better experiment.