When you examine a top-quality chocolate bar or a well-made dipped truffle, you'll see that the chocolate is shiny, firm enough to tap with your fingernail, and will break with a sharp snap. That's because it's tempered. Tempering is a process that encourages the cocoa butter in the chocolate to harden into a specific crystalline pattern, which maintains the sheen and texture for a long time.
When chocolate isn't tempered, it can have a number of problems: it may not ever set up hard at room temperature; it may become hard, but look dull and blotchy; the internal texture may be spongy rather than crisp; and it can be susceptible to fat bloom, meaning the fats will migrate to the surface and make whitish streaks and blotches.
Anytime you need chocolate to be firm at room temperature and to have a glossy sheen and a crisp texture--as you would with chocolate nut clusters, dipped candies or decorations like chocolate leaves or ruffles--you must temper the melted chocolate. For tempering, always use top-quality dark, milk or white chocolate. Compound chocolate, which is a lower-quality chocolate, contains other fats beside cocoa butter, so it often doesn't need tempering. And chocolate that's combined with other ingredients, as in a chocolate cake or mousse, doesn't need to be tempered.
Beta crystals: the goal of tempering —
Tempering seems like a mysterious process because you can't really tell what's happening; instead, you need to learn to control the process only by temperature, by sight, and by touch.
When chocolate is melted and cooled, it can crystallize into any one of six different forms. Unfortunately, only one of these—the beta crystal, or Form V—hardens into the firm, shiny chocolate that cooks want.
Traditionally, pastry chefs and chocolate manufacturers use one of several tempering methods that all contain the following stages:
Stage one: Melting the chocolate so that the cocoa butter melts completely. Most cooking literature advises you not to get the chocolate over 120° F for fear of burning the cocoa solids, or causing the chocolate to irreversibly separate into solids and fat. But melting curves of chocolate in the technical literature indicate that most of the fats in cocoa butter aren't melted until 122° F, and some processors recommend heating their chocolate even higher—up to 131° F. If you're serious about perfecting tempering, you should consult the manufacturer of the chocolate you're using for the best temperature. Cocoa beans from different locations vary: at the same temperature, cocoa butter from Malaysian beans grown near the equator will be firm, while cocoa butter from Brazilian beans grown in a cool climate will be very soft.
Stage two: Rapid cooling to about 82° F for dark chocolate (79° F for milk and white chocolates). This gets the crystallization of the good beta crystals started, but it does allow some undesirable beta-primes to form, too.
Stage three: A slight warming, first back to 86° F for dark (84° F for milk and white) where it's held for a few minutes to let the beta crystals continue to form, and then a final warming to 89° to 91° F for dark and 87° to 89° F for milk and white. This final increase in temperature melts the undesirable beta-prime crystals that were formed.
Stage four: Verify that your chocolate is indeed in temper. Smear a thin layer onto a piece of parchment or waxed paper, then wait five minutes and try to peel the chocolate from the paper. If it peels easily and the chocolate is shiny, not blotchy, you're fine. If not, start the tempering process again.
A radical shortcut to tempering —
When you buy blocks or pastilles of good-quality chocolate from the manufacturer, that chocolate is already tempered. Is there a way to just maintain that temper and avoid going through the whole process again? I learned from an internationally renowned chocolate expert, Dr. Paul Dimick, Professor Emeritus of Food Science at Pennsylvania State University, that this is indeed possible. The good beta crystals don't melt until 94° F, so if you never heat chocolate over 91° to 92° F, you won't lose them and your melted chocolate will remain tempered. The trick is to barely melt the chocolate. Chocolate begins to melt at about 89° F. Start by grating or finely chopping the chocolate so it melts evenly. Put the chocolate in a metal bowl and warm it over very low heat -- an electric heating pad is a neat idea. Stir constantly until about two-thirds of the chocolate is melted. Take the bowl from the heat and continue stirring until all the chocolate is melted. For dark chocolate, you want the whole mass to end up at 89° to 91° F (87° to 89° for milk and white). As long as you haven't exceeded 92° F, your beta crystals should be fine.
You do need to be sure that the chocolate you start out with is truly in temper. Chocolate that has been stored improperly or for a long time may look all right, but it could be on its way to losing its temper. If you use this shortcut method, you should still test the chocolate on parchment or waxed paper to make sure that the chocolate sets up hard and shiny.