I read somewhere that when you roast Chestnuts, you only need to poke their shells with a fork.
This is what raw Chestnuts look like. They are inside of their outer shells. The picture was taken by, Benjamin Gimmel, Wikipedia Commons.
This is a picture of Chestnut trees by, Schmzo WC.
When I poked the Chestnuts with a fork and put them in the oven, it wasn’t long before they exploded. The water in the Chestnuts expanded and them broke the shells. When water gets hot enough, it becomes steam. When it gets cold enough, it becomes ice.
Before this I had always sliced the flat part of the shell with a knife. I went back to this after the experiment. I’d get someone who knows how to slice the Chestnuts. We have to be very careful around knives. This is just a little warning I feel the need to give.
Two example of expansion. The first is railroad tracks that contract in the cold and expand in the heat. They buckle. The picture is by, US Government.