Dark chocolate must contain at least 34% cocoa ingredients, but the higher the better the chocolate. The preference for dark chocolate is 60% cocoa, the real lovers prefer 70% - 80%. The better the quality of the chocolate, the less sugar it contains. Sugar is like salt i the food, it increases the taste, but too much is not good.
Good chocolate contains vanilla, an expensive flavoring made from an orchid from Madagascar. It also contains a bit of lecithin, a vegetable stabilizer. Unsweetened chocolate, only to be found at specialty stores, contains 98% cocoa components.