Tempering chocolate is one of those things that seems really scary if you've never done it before. I have to admit, when we learned tempering in pastry school, it could get really frustrating (especially in the summer when the A/C wasn't working). But with a little practice, you'll start to recognize the signs of tempered chocolate more and more quickly until you're tempering like a pro.
The Science Part
I like to think of the science behind tempering it in terms of bricks. If you're going to build a structure that's sturdy and even—and likely to stay that way—you want to use bricks that are all the same size, are evenly stacked, and fit tightly together. Right? Right.
Well, cocoa butter's structure is crystalline. There are several different shapes and sizes of crystals ("bricks") and you want to make them all the same size.
If you just melt chocolate and let it set up, the bricks are scattered all over the place—giving it a dull, mottled appearance and soft texture. When you temper, you're making sure the bricks in the cocoa butter are the right kind: uniform in size and shape, and stacked tightly together. This is what gives tempered chocolate its desired characteristics: a smooth glossy surface, a nice "snap" when you bite into it, and better resistance to melting and scuffing.
"So, miss smarty-pants," I hear you say, "how exactly DO you temper chocolate?" I'm so glad you asked.
Really, You Can Do It
There are several ways to accomplish your lofty goal of beautiful, shiny chocolate, but we'll stick to the simplest one—it's called seeding. The basic process of seeding is to heat your chocolate, add some already-tempered chocolate, and stir the hell out of it as it cools down. Just be sure to use a high-quality block or chunk chocolate, and not chips! Chocolate chips have additives that help them keep their shape during baking, which affects the tempering process (and you don't want them around in this case).
Do you need a tempering thermometer? They're a must while learning and available online or at specialty kitchen stores for about $10 to 15. After a while you might not need it, but to start you'll really want it so you can get familiar with the different temperatures at which you'll need to have your chocolate.
Step One: Melt
Chop your chocolate into chip-sized pieces and melt about half of it in a bowl over a saucepan of simmering water, stirring occasionally. Once it's melted, check the temperature.
For dark chocolate you want around 115°F. For milk or white, 110°F.
Remove it from the saucepan and wipe the moisture off the bottom of the bowl.
Note: Chocolate + water = trouble.
Step Two: Seed
What you'll do now is stir the melted chocolate with a spatula. Stir like your life depends on it. As you stir, add the rest of the chopped chocolate bit by bit—add some, let it melt, add some more. And keep stirring! The more it's agitated, the nice-n-shinier it'll be.
For dark chocolate, you want to get it down to about 90°F. For milk or white, 88°F.
This will take you about 15 minutes, give or take depending on how much you're tempering, and how warm the chocolate was to begin with.
Step Three: Test
Once the chocolate is close to the desired temperature (a degree or two above is fine) you'll want to test it. Take a metal knife or spoon and dip it in the chocolate, then stick that in the fridge (1 to 2 minutes for dark, more like 4 to 5 for milk and white). If the test comes out of the fridge totally set up—not tacky to the touch, a little glossy, not streaky or blotchy—then huzzah and kudos to you! You just tempered chocolate.
You can lord that over all of your friends at your next dinner party. If the chocolate is setting up too quickly for you to work with, you can re-warm it very carefully over the saucepan—but don't go over 92°F!
Not Working? Don't Freak Out
A few things might be going on:
If it's sticky or soft to the touch, it's not tempered yet. Keep stirring! And get that temperature down. Once it's there, test again. You should be fine.
If it's firm and shiny but looks streaky, it's probably in temper. You just need to agitate it more. (I promise, you do this enough and you'll have forearms like the Incredible Hulk.)
If the chocolate doesn't set up even after you've gotten it down to the correct temperature and stirred the crap out of it, please don't hurt me but, you should start over. I know, it's unfair, but chocolate is very finicky. Ambient temperature, humidity, and many other factors out of your control can have an adverse effect on how chocolate decides to temper (or not). Hell, why do you think they call it "temper?" But practice makes perfect, and once you do get it, which you will, it'll be that much more rewarding.
1. Chop your tempered chocolate into chip-sized pieces, reserving half for seeding, and melt half of it to about 115°F.
2. Remove the melted chocolate from the heat and stir with a silicone spatula while seeding with (adding) the reserved chocolate, a bit at a time.
3. When the chocolate has reached about 90°F, test on a knife or spoon that has been placed in the fridge.
4. Once temper has been achieved, the chocolate can be warmed slightly (to 92°F) to make it easier to work with.