Dark Crystal

Reader Evelyn wants to know: why does tempered chocolate have a higher melting point than untempered chocolate? When I wake up to a food science question like this I can only say: life is good.

The answer is that it all has to do with crystals. As regular Joe Pastry readers know, crystals abound in the kitchen. Certainly in the salt shaker and the sugar bowl, but in lots of other places besides. There are starch crystals (in bread) and fat crystals (in solid fats like butter). There are even such things as protein crystals, though I honestly don’t know where (or if) they occur in the kitchen. Will a real scientist please stand up?

Chocolate contains fat crystals, at least when it’s in solid form. As I mentioned yesterday, cocoa butter is unusually uniform in its composition, made up of just three different types of fats. That uniformity makes cocoa butter extremely crystal-prone, because similar molecules are wont to stack up on one another like LEGOs under the right conditions (the individual molecules form masses, stop flowing, and voilà you go from a liquid to a solid crystal).

But here’s the rub: depending on the way in which cocoa butter is allowed to cool and harden, there are six different types of crystals that the fat molecules can form. Just two of those are stable and uniform, the rest are comparatively unstable and random. Tricking the fat molecules into forming only (or at least mostly) the stable, uniform kind is what tempering is all about.

But I digress. A bit. The interesting thing about those different crystal formations is that they all have different melting points. The more random, less stable crystals have a lower melting point (around 86 degrees Fahrenheit), while more the uniform crystal formations have a higher melting point (around 91).

It’s the higher melting point that’s partly responsible for tempered chocolate’s firmer texture and more brittle “snap” vis-à-vis untempered chocolate which is softer, duller and more pliable at room temperature.