When cocoa butter crystals in chocolate harden into a stable crystalline pattern, the chocolate is said to be in temper. All chocolate leaves the manufacturer in temper, but when stored incorrectly, it may go out of temper. When melted, it goes out of temper, too. A process called tempering restabilizes the crystals so that when the chocolate cools and rehardens, it is smooth and glossy and breaks with a satisfying snap. When untempered chocolate cools, it is dull and grainy and may even remain soft or sticky.
Tempering is done by heating and cooling the chocolate to particular temperatures. Different chocolates require different temperatures. Chocolate that is to be used in cakes, cookies, brownies and mousses does not need to be tempered. Candymakers, however, must temper chocolate for dipping or enrobing.
To use chocolate for dipping without tempering it, melt the chocolate with 2 tsp. of vegetable shortening for every 8 oz. of chocolate. The shortening will keep the chocolate looking shiny and smooth after it cools.
Adapted from Williams-Sonoma Kitchen Companion: The A to Z Guide to Everyday Cooking, Equipment and Ingredients (Time-Life Books, 2000)