Cooling and demoulding

Cooling looks like waiting and is a controlled operation. Chocolate leaving a moulding head is correctly tempered liquid; what happens over the next several minutes decides whether the finished bar has gloss, snap and a clean release, or whether the work done in tempering is thrown away.

At industrial scale this is a cooling tunnel with zones at different temperatures, through which moulds travel on a belt. The profile is usually gentle at first, colder in the middle where most of the crystallisation heat has to be removed, and warmer again at the exit so bars do not meet warm humid air while still cold.

The release mechanism is contraction. Cocoa butter in its stable crystal form occupies less volume as a solid than as a liquid, so a correctly tempered and correctly cooled bar shrinks slightly away from the mould walls and drops out under its own weight with a tap. A bar that will not release has almost always failed earlier — poor temper produces less contraction — which makes demoulding an unusually informative quality check: the mould tells you about the temper before anybody tastes anything.

After demoulding the chocolate is set but not finished. Crystallisation continues for days, and that is why bars are commonly rested before packing.

Removes the heat of crystallisation at a controlled rate, allowing the stable cocoa butter crystal form seeded in tempering to propagate through the whole mass, and produces the volume contraction that releases the bar.

Cooling too fast traps unstable crystal forms and produces a dull, soft bar that blooms early. Cooling too slowly lets fat migrate and coarse crystals form, with the same visible outcome by a different route. Exiting into warm humid air causes condensation on cold chocolate, which dissolves surface sugar and leads directly to sugar bloom.