After conching, dark chocolate is essentially a warm fluid mass of cocoa butter that contains suspended particles of the original cacao beans and of sugar. Milk chocolate also contains butterfat, milk proteins, and lactose, and proportionally less cacao bean solids.
The last step in manufacturing chocolate is to cool the fluid chocolate to room temperature and form the familiar solid bars. It turns out that this transition from fluid to solid is a tricky one. To obtain stable cocoa butter crystals and a glossy, snappy chocolate, manufacturers carefully cool and then rewarm the liquid chocolate to particular temperatures before portioning it into molds, where it finally cools to room temperature and solidifies.