Both bittersweet chocolate and semisweet chocolate are types of sweet dark chocolate.
In general, bittersweet is heavy on the cocoa solids and light on the sugar while semisweet is moderate on both the cocoa solids and sugar content.
Most bittersweet bars contain at least 50% chocolate liquor, with especially high-quality ones pushing 70-80% cocoa liquor. Neither one contains milk in either liquid or dry form.
Even though bittersweet has less sugar and more liquor than semisweet chocolate, the two names are used interchangeably. "Bittersweet" generally refers to European dark chocolate, while "semi-sweet" is primarily an American term, popularized by Nestlé Toll House chocolate chips.
According to the Chocolate Manufacturers Association, U.S. government standards require that bittersweet chocolate contain at least 35% chocolate liquor while semisweet can
But, since there is no government standard for sugar content, and since semisweet chocolate can contain up to 35% liquor, the two could contain practically identical amounts of chocolate liquor and sugar and still retain their bittersweet and semisweet labels.
One brand's bittersweet could be close in sweetness to another brand's semisweet chocolate, and vice versa.
Both of these types of chocolate are commonly used in baking and are sometimes referred to as 'couverture' (chocolate that contains at least 32% cocoa butter).
Couverture is a favorite for dipping, coating, and molding. When melted, it is smooth and fluid, and when it hardens, it has a lovely sheen and a creamy texture.
Since both types fall into the “dark chocolate” category, they're a good source of certain flavonoids that may be protective for the heart.
Recent studies have revealed certain health benefits from the regular consumption of small quantities of dark chocolate.