Tempering is a procedure where pure chocolate is stabilized through a carefully controlled melting-and-cooling process, which allows the cocoa butter molecules to solidify, and for the chocolate to harden properly. Commercial chocolate, such as a candy bar, is already tempered, but this condition changes the minute you melt it for your own use; the molecules of fat separate (as cream separates from milk). In order to restore them, you must temper the chocolate.
Tempering determines the final gloss, hardness and contraction of chocolate. At each step of the tempering process the temperature of the chocolate must be precise and uniform. A tiny variation can ruin the result.
Tempering isn't necessary for all recipes, but is done when the chocolate will be used for candy making such as molded chocolates or dipped centers, as well as more extensive decorations, such as sculptures or ribbons. Without tempering, the chocolate does not harden properly as the cocoa butter separates, but when tempered; the chocolate is more manageable and glossy when it sets.
The two most common problems of working with chocolate are SEPARATING and SEIZING. There are steps to follow which ensure that neither separation nor seizing occur:
Separation-the cocoa butter separates from the rest of the ingredients because it has gotten too hot. A gray or white film, known as BLOOM can be seen on the solidified chocolate. Once visible, there is no way to salvage the chocolate from bloom.
Seizing-the chocolate becomes clumpy of stiff from an exposure to moisture, or becoming burnt. Once seized, chocolate can be used only in bakin recipes
Some theorists suggest storage of tempered chocolate confections should be at room temperature, while others may use some sort of refrigeration. Most lean toward room temperature because the chocolate may "bloom"-that is the cocoa butter starting to separate out from the chocolate, and forming a thin layer of cocoa butter on the surface. Chocolate is not affected, taste-wise, if they bloom, but the aesthetics strongly decrease. Fat absorbs heat at a different rate than the other ingredients in chocolate, so it's unstable and floats to the surface, as cream would float to the surface of milk.