What's the difference between the following chocolates?
If a chocolate only lists the % cocoa solids used, can I figure out which of the above types it is?
Milk chocolate is unique in that it contains a significant quantity milk, either in the powdered, liquid, or condensed form.
Dark chocolate is a category of chocolate that includes semisweet and bittersweet chocolate. The US FDA actually does classify dark chocolate as anything containing 35% or more cacao (liquor or butter). In practice, semisweet chocolate is typically much sweeter, and contains about 50% sugar. Bittersweet chocolate, on the other hand, typically contains about 33% sugar. Some dark chocolates may contain small amounts of milk, but not enough to be called milk chocolate.
In the US, the government regulates the use of certain chocolate terms. Their distinctions for chocolates have to do with the chocolate liquor content and not the total amount of cocoa products (the cocoa fat and the other solids). The regulations also do not distinguish between bittersweet and semisweet. To them it is all sweet chocolate. Based on Callebut labeling, milk chocolate has about 32% cocoa content and dark chocolate 51% or more.
In practice you will find chocolates with 40% or more labeled as either semi-sweet or bittersweet. Semi-sweets are supposed to have more sugar, so if we use the nomenclature adopted by Ghirardelli (a common choice for cooking in the US) that means 53% of the chocolate product is sugar, whereas for bittersweet they use 40% (based on chocolate chips).
If you look at the Nutrition Facts label, the total amount of sugar in a portion is listed together with the weight of the portion. For example, for the 55% Chocolove bar, it is 13/30 = 43%, so this Chocolove would be in the bittersweet category.