On Food and Cooking

cocoa butter that contains suspended particles
of the original cacao beans and of sugar. Milk
chocolate also contains butterfat, milk
proteins, and lactose, and proportionally less
cacao bean solids.
The last step in manufacturing chocolate is
to cool the fluid chocolate to room
temperature and form the familiar solid bars.
It turns out that this transition from fluid to
solid is a tricky one. To obtain stable cocoa
butter crystals and a glossy, snappy chocolate,
manufacturers carefully cool and then rewarm
the liquid chocolate to particular temperatures
before portioning it into molds, where it
finally cools to room temperature and
solidifies.
Cooks often melt manufactured chocolate
in order to give it a special shape or to coat
other foods. If they want it to resolidify with
its original gloss and snap, then they must
repeat in the kitchen this cycle of warming up
and cooling down, or tempering (p. 709).