Chocolate is made from cocoa beans, which are fermented, then dried, then roasted in order to bring out their flavor. After roasting, the beans are cracked into cocoa nibs. The nibs contain 53% cocoa butter and 47% cocoa solids.
Next, the cocoa butter is separated from the cocoa solids. The nibs are ground into a thick paste (cocoa mass or chocolate liquor). Then, the paste is pressed so all the cocoa butter is squeezed out. What’s left is 100% pure cocoa solids.
The differences between chocolates depend on the flavor profile of the beans used, the proportion of cocoa solids to sugar to cocoa butter, and the amount of refining and processing. In the US, to be labeled as dark chocolate, it must contain at least 35% chocolate (total amount of cocoa solids and cocoa butter). In the UK, it must contain at least 42% chocolate. Milk chocolate must contain 10% chocolate and 12% dairy.
In less expensive chocolate, the cocoa butter is replaced by other fats. Since these fats have a higher melting point than cocoa butter, chocolate made with them doesn’t melt in your mouth the way that high quality chocolate does.