Q: I have semisweet chocolate squares that have turned white. Can I still use them?
A: The white haze is called bloom. It's caused by cocoa butter rising to the surface, and it happens to chocolate when it is stored in a place that is too warm.
Chocolate is like Goldilocks: It likes to be just right, not too warm and not too cold. Storing it in the refrigerator isn't great because it can get damp, which can make it grainy.
The best place to keep it is in a dark cabinet that stays between 60-70 degrees. In most kitchens, that means the cabinet that is farthest from the stove. It also picks up other flavors easily, so wrap it well.
The good news is that bloom doesn't mean you can't use the chocolate. It will disappear when you melt it in a recipe. But taste a bit to make sure it hasn't picked up an off flavor.