Chocolate that contains chocolate liquor, sugar, cocoa butter, vanilla and leicithin (an emulsifier).There are no milk solids added in dark chocolate. The cocoa content of commercial dark chocolate bars can range from 30% (sweet dark) to 70- 80% for extremely dark bars. Bittersweet chocolate and semi-sweet chocolate also fall into the “dark chocolate” category.
In addition to containing cocoa butter and chocolate liquor, milk chocolate contains either condensed milk (most European varieties) or dry milk solids. Milk chocolate must contain at least 10% chocolate liquor (in the United States), 3.39% butterfat, and 12% milk solids. Milk chocolates are typically much sweeter than dark chocolate, and have a lighter color and a less pronounced chocolate taste. Milk chocolate is more difficult to temper properly and more prone to overheating.
White chocolate
White chocolate gets its name from the cocoa butter it contains, but does not contain chocolate liquor or any other cocoa products. As a result, it has no pronounced chocolate taste, but commonly tastes like vanilla or other added flavorings. By law, white chocolate must contain a minimum 20% cocoa butter, 14% milk solids, and a maximum of 55% sugar. There are some “white chocolate” products available that contain vegetable fats instead of cocoa butter—these should be avoided from a taste standpoint, as they contain no cocoa products at all, and are not technically white chocolate.
*Adapted from:
http://candy.about.com/od/candybasics/a/chocguide.htm