Question: Why do you love chocolate?

Lynne Thomas answered on 17 Jun 2014:

I love chocolate because it is so tasty! And it melts in my mouth in a nice smooth way.

In fact there is a lot of science in chocolate. When they make chocolate they use a process called tempering. What this is, is a recipe for heating and cooling the chocolate and stirring it in exactly the right way that gives us the chocolate that we like to eat. If they get it wrong, the chocolate doesn’t melt in your mouth any more and is brittle and gritty.

This is all because of the cocoa butter molecules and the way that they are arranged in the solid. If you leave chocolate and it melts and then goes hard again, it goes white on the surface which is something called blooming. The same thing happens if you leave chocolate for a long time and it gets old.

What is happening is the molecules of cocoa butter are forming slightly different solids. If you imagine you are tiling a driveway with bricks. You could put all the bricks on the drive so that they were parallel much like a brick wall. Or you can do one of the more fancy patterns (called herring-bone) where then bricks are tilted. You can still fill all of the driveway and the bricks are exactly the same size and shape. The same thing can happen in crystals where you can put the molecules into a three-dimensional grid in slightly different ways. Its called polymorphism.

In cocoa butter, there are six different ways you can do this! Four of these solids melt below room temperature so would make a very messy chocolate bar! One of them melts at your body temperature which is the one we like to eat. The final one melts a few degrees higher in temperature so no longer melts when you put it in your mouth. Its this last one that you are getting when chocolate melts and resolidifies or if you leave it to get really old. Nothing has happened to change the chemistry of the cocoa butter molecules, it is just a rearrangement of the solid and it does this all by itself!