Think of tempering as the alchemy of chocolate. Tempered well, chocolate is glossy, breaks with a crisp snap, and melts smoothly in the mouth; if this step is skipped or done poorly, chocolate becomes gray, crumbly, and almost dusty as it hardens.

Tempering is a way of "freezing" liquid chocolate. Water freezes in much the same way, except, of course, that the temperature at which water freezes is much lower. Freshly made liquid chocolate first enters a bowl on the tempering machine at 105°F. It then flows into a jacketed steel tube that cools the chocolate to about 85°F and then heats it to 91°F. The purpose of these temperature changes is to create a specific type of cocoa butter crystal that will eventually multiply until there are enough crystals to turn chocolate from a liquid to a solid.