Book 27, Question 69
Why is butter hard in the fridge but soft on the counter?
Butter contains fat that forms tiny crystals when it is cold.
The crystals interlock like a mesh and make butter firm. As it warms, some of these crystals melt, so the butter becomes softer and spreadable. Butter doesn't melt all at once because it holds different kinds of fat crystals, which melt at different temperatures. That's why it goes slowly from hard to soft to liquid.