What is the purpose of tempering chocolate?

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.

Tempering, in scientific terms, is a process of encouraging the cocoa butter to form a stable From V crystal structure.

When you temper chocolate, you are first melting the chocolate to a temperature that will break all of the crystals, leaving you a more or less uncrystalized soup of melted chocolate. From this clean starting point, you somehow encourage the chocolate to form only the right kind of crystals (Form V). This can be done either by adding pre-tempered chocolate as the melted chocolate cools or by agitating the melted chocolate on a marble slab. The former method is obviously much easier.

All real chocolate (including bars, most chips, and courverture) is sold in tempered form and must be in temper to use. The best way to use this chocolate is by melting it fully and adding unmelted tempered chocolate, but, if the chocolate you are starting with is tempered, you can also melt it very slowly until it is just barely melted it should remain in temper.

As far as the practical differences, tempered chocolate:

• Glossy finish
• Hard snap
• Higher melting temperature
• Will not have fat bloom (white splotching after hours to days)
• Sets in 5 minutes or less

I wondered this myself over the holidays when I wanted to dip some cookies in chocolate. I couldn't be bothered with buying a thermometer and figuring out how to do the tempering, so I just melted the chocolate (some nice quality chocolate bars, so not special chocolate meant for dipping) gently in a double boiler (ok, metal bowl on top of a pot of water), dipped, then set things on parchment paper. It took a few hours to set and it probably would melt if you sat with it in your hand, but it worked well enough for me. I stored the cookies at room temperature and they didn't seem noticeable melty when we ate them.

The beauty of chocolate is that it firm, crisp and solid at room temperature however when at body temperature like in our mouths it melts.

The simplest explanation of the effects of tempering chocolate is that the melting temperature increases when the chocolate crystallizes so it melts in your mouth and not your hands. Also, the texture of the chocolate is finer as cooled untempered chocolate has a grainy texture on the tongue.

Years ago I watched Pierre Herme who was at that time executive pastry chef of Fauchon in Paris put a plastic bowl of chocolate in the microwave until half was melted and then use a handheld electric blender to mix the melted and unmelted chocolate together to create a perfect tempered chocolate for dipping.

Perhaps, the easiest way to temper chocolate is to grate half the chocolate with a vegetable grater and melt the other half in a plastic bowl in the microwave until it is all just above body temperature. Then with a spoon stir in the grated chocolate. This is called the 'seeding' method. If the chocolate begins to get too cool just place it in the microwave for 2 or 3 seconds without melting it again.

Put your Hershey bar in your car's glove box. Wait for a hot day. Remove it. Fix the situation by putting it in your fridge.

Now taste it. That is what chocolate that is way out of temper tastes like. It is still chocolate, but something is clearly, terribly, wrong.