Unsweetened chocolate and bittersweet chocolate are both dark chocolates. Unsweetened chocolate (also called baking chocolate) is 99 percent cocoa liquor (which is part cocoa butter and part pure cocoa). Bittersweet chocolate, by FDA regulations, must contain at least 35 percent cocoa liquor--but it can contain as much as 84 percent. Because the difference is largely made up by sugar, this creates a product of widely varying sweetness that goes by the same name.
Fill the bottom of the double boiler about halfway with water and place on high heat. Bring to a boil.
Reduce heat to medium or medium low to bring water to a steady simmer.
Break or cut chocolate into chunks or squares. Place upper pot inside lower pot, on top of the boiling water. Add unsweetened chocolate.
Stir chocolate frequently to encourage smooth melting.
Add 1/2 tsp. to 1 1/4 tsp. sugar per ounce of unsweetened chocolate, depending on how sweet you want your bittersweet chocolate to be. Stir frequently to ensure even distribution of sugar. You should also add any additional spices at this time.
If a hard chocolate is desired, pour semisweet chocolate into a mold to harden. Otherwise it is ready for use. Chocolate will harden quickly after it is removed from heat.
You may want to add additional cocoa butter to your mixture. Cocoa butter is especially good for chocolate that will be used for dipping and melting.
Quality of cocoa beans (and processing) does make a difference. Cocoa beans grown in different areas of the world also yield chocolate of varying flavors and textures. South American cocoa beans, for example, create chocolate that is more fruity, nuanced and rich than the cocoa beans grown in African nations.
If you do not have a double boiler, you may use two pots that are similar in size. Place the smaller pot inside the larger pot, and use less water. It is very important to prevent water from mixing with the chocolate.
Chocolate should be stored in a cool, dry place. When it gets too warm, it develops a light brown powdery surface called "bloom." This occurs when the cocoa butter separates and rises to the surface. Chocolate with bloom is still perfectly edible. To restore the uniform nature of the chocolate, simply melt according to directions above.
Don't let even a drop of water into your chocolate mixture. Water will turn your smoothly melting chocolate into a thick, grainy, clumpy mixture.
Linda Basilicato has been writing food and lifestyle articles since 2005 for newspapers and online publications such as eHow.com. She graduated magna cum laude from Stony Brook University in New York and also holds a Master of Arts in philosophy from the University of Montana.