Chocolate – Bizarre: Chocolate tempering is good on the outside

Chocolate is an odd substance when it comes to melting and hardening. When chocolate hardens, its melting point will end up being just a few degrees higher than the hardening temperature.

When chocolate crystallizes at high temperatures, it forms a strong, dense crystalline structure that, texture-wise, is quite brittle. Most bought chocolate (baker's chocolate and chips) is already tempered, but when you melt it, you break down that crystalline structure, and if you harden it at room temperature then it ends up forming very weak crystals that will melt in your hand.

If you use a special coating chocolate (couverture or the lower-quality compound chocolate) then you don't need to worry so much about tempering (although it's still a good idea), but if you use ordinary chocolate and don't temper it then your coating will end up being messy and wet and rub off on your hands while you eat it. It might even melt while stored.

Tempering is the key to making a room-temperature-stable chocolate coating. If you don't do this, you'll need to keep your pastries refrigerated until they're ready to consume.

To answer your last question: yes.

Regarding the previous question, it's because the temperature at which the cocoa butter in the chocolate crystallizes affects the overall consistency of the chocolate. If you've ever eaten a chocolate bar that was left in a car on a hot day after it has cooled down again, and who hasn't, you'll know about this. Sometimes chocolate tastes fine but has a definite 'grittiness' to it: other things being equal, that's usually because the cocoa butter crystals are too large.

Cocoa butter has a number of different crystal forms, each of which will have a slightly different effect on texture and melting point. When melted chocolate sets, the cocoa butter crystallizes, and it will generally all crystallize with the structure that it starts to crystallize with. (This process where crystals start to grow is called nucleation.)

So you want to have control over the temperature at which crystallization starts. The optimum crystal form for nice chocolate will tend to predominate when crystallization starts somewhere between 18-25 degrees C (around 64-77F).

So if you think about it: when you add room temperature stuff (like a pretzel) to chocolate that is considerably hotter than room temperature, the resultant temperature on the surface of that pretzel will likely be way higher than 18-25 degrees. On the other hand, if you are dipping an item that is significantly below room temp, then your chances of hitting that window are much higher.

The surface structure of the thing being dipped can of course make a difference to crystallization as well, but for normal purposes that is marginal. To put it another way, it doesn't matter what ingredients you're dipping - temperature is key!