Why temper chocolate? Because chocolate is a lot like steel. When melted chocolate becomes solid again, it's important that it has the right crystal structure. It's been 25 years since I took metallurgy, and I don't remember much, but one thing I do remember about tempering steel is that the different phases of tempering results in different crystallography, and thus different material properties. Different kinds of steel are used for different things - you might want to use a certain kind of steel to make a car door, a different kind to make an I beam, etc. Steel has all different kinds of properties, and that's a good thing. Same with chocolate.
When melted chocolate returns to solid form the cocoa butter in the chocolate forms a crystal structure, and the crystal structure it takes on depends on the temperature at which they are formed. If the chocolate is allowed to cool on its own, the crystals of fat will be loose, resulting in a chocolate that is dull in appearance, soft & malleable, and greasy to the touch. It won't "set up right", in candy speak. While tempering, the goal is to keep the chocolate above that temperature so that the cocoa butter actually forms a dense crystalline structure. Holding the chocolate at this temperature and stirring will allow a whole bunch of these stable crystal structures to form providing a lot of seed crystals to form in the chocolate. When the chocolate is finally allowed to fully cool, if there are enough stable seed crystals, then the chocolate will harden into a very stable hard chocolate with a slight sheen, snap when broken, and hold a nice shape. In candy talk, it will "set up well" and it will also prevent blooming of the chocolate - unsightly light brown streaks. So to make candy, you can't just melt chocolate any old way.
Some other things to know about chocolate for candy making:
- You have to use real chocolate for chocolate making - not a bag of chocolate morsels to use for baking. At the grocery store, you can buy bars of Ghirardelli baking chocolate at various percentages and those have worked really well for me. I just recently bought some on sale at Busch's that were 3 for $5. That works out to about $6.66 per lb. It's a little extra work, because you will have to chop it up into small pieces. Chocolate for chocolate making comes in drops, but if you are just getting started with chocolate making, I'd suggest going with bars from the grocery store.
- Don't bother with the double boiler. The microwave is a much better tool for chocolate making. Double boilers are a pain to do anything in, especially chocolate tempering. At my house, the microwave is just sitting there, waiting to reheat last night's dinner leftovers or to make a bag of popcorn. It's good to have another use for it. (by the way, making rice is also another great use for the microwave, but I will save that for another post).
- Great tip I learned from Tammy - use a plastic bowl for tempering chocolate - it retains less heat than glass. I have some Tupperware Rock and Serve containers that work well for me.
- To temper a pound of chopped up dark chocolate, microwave it for a minute and stir, and return it to the microwave for about 30 seconds and stir again, and keep doing this (reduce how many seconds you wave it as it gets closer to being done) until is about 75% melted. Once it's that far melted, just keep stirring it until it's all melted. Check the temperature....the goal is to get it to 90 F without going over.
- If you blow it and go over 90 F, all is not lost. Return the chocolate to the microwave and heat it to 115-120 F. Don't go over. Then add about 4 oz. of finely chopped chocolate that is already tempered (this is called seed chocolate). Bars of baking chocolate are already tempered, so that will work. This gives the cocoa butter some crystals of the already formed chocolate to glom onto. Remember back in high school chemistry where you made crystals? No, of course you don't! Anyway, what you learned and forgot is that crystals beget other crystals. Once a crystal has formed, it's easier for others to form on it. Crystals need friends!
- How to know if your chocolate has tempered? Dip your finger in and smear it on a piece of parchment paper. It should set up and get hardin a couple minutes. You can put it in the fridge to hasten the process. If not, go back and do a redo like described above. Chocolate is very forgiving.