Bittersweet chocolate and semisweet chocolate can have a very similar ratio of chocolate liquor to sugar. Many chocolate manufacturers now state the percentage of chocolate liquor in their product on the label (you may have to look closely, but it could be there). Some brands are 70 percent chocolate liquor or even higher. The more chocolate, the less sugar, and some of these chocolates can be quite bitter. In my experience, it takes a very particular recipe to support a chocolate with a very high liquor content. Also, some chocolates with a high liquor content can affect the viscosity of the icing.
