Bittersweet and semisweet chocolate are sometimes used interchangeably. But true to its name, bittersweet is not as sweet as semisweet. It's available in packages of 1-oz. squares, chips and candy bars.
Store chocolate tightly wrapped in a cool, dry place. When chocolate is stored in a spot that's too warm, it develops grayish-white streaks or blotches called a fat bloom. In damp storage, it develops a rough feel, called a sugar bloom. You can still melt chocolate with blooms and incorporate it into batter or dough for baked goods.