Just for you, Marilyn--from today's Oregonian. (article copied inside in case link expires)
It's as simple as microwaving popcorn
Making bark starts with tempering chocolate, and it's not the tricky job people think it is Tempering isn't difficult to do, but it helps to know a bit of the science behind the process before you begin. Unless it has been stored improperly along the way, the chocolate you buy at the store comes already tempered. It's shiny, hard and doesn't melt as soon as you touch it. But when you heat the chocolate above 90 degrees, you melt the network of crystals (called beta crystals) that give it that crisp and glossy structure. As the chocolate cools, "bad" crystals form and the finished product will feel tacky and look dull, like it's been sitting in your pantry for years.
That's fine if you're going to use the melted chocolate in a recipe, but if it's meant to be used as a bark or for a coating for a candy or dipping fruit, you'll want to get it back into temper so it sets up glossy and snappy again.
This means rebuilding that network of beta crystals. The easiest way for home cooks to do this is to stir in chunks of tempered chocolate (i.e. unmelted store-bought) to the melted stuff. The tempered chocolate acts as a "seed," offering its own beta crystals, which encourage more of these good crystals to form in the melted chocolate. Stirring ensures that those good crystals get distributed and make even more.
Strangely enough, the temperature at which these crystals melted in the first place is the same temperature at which they form as the chocolate cools -- between 88 and 91 degrees.
Confusing, right? Well, here's how that works: When melted chocolate cools down quickly, beta crystals don't have a chance to form. "Bad" crystals, which form at a lower temperature, take over instead. By holding the melted chocolate between 88 and 91 degrees, you give the beta crystals a chance to form first.
The Microwave Method:
For 1 pound batches (like barks), the microwave can't be beat. It's fast and requires just one bowl. 1. Chop the chocolate into uniformly small (about 1/2-inch) pieces so it'll melt quickly and evenly. 2. Set the microwave at 50 percent power and put about three-quarters of the chocolate in a glass or ceramic bowl. Heat for 30 seconds, stir and repeat until about three-quarters of the chocolate in the bowl is melted. It should take about 3 minutes total. 3. Check the temperature of the chocolate. When it's around 100 degrees, add the reserved chopped chocolate and stir until it's melted and the temperature has reached tempering range: 88-90 degrees for dark and semisweet, 86-88 degrees for milk, 80-82 degrees for white.
The Double-boiler Method:
The method is similar when using a double boiler; just make sure the water is at a gentle simmer and not even a drop of it gets into the bowl of chocolate. Melt three-quarters of the chocolate until three-quarters of it is melted, then, when the temperature is 100 degrees, add the rest of the chopped chocolate, stirring until all the chocolate is melted and it's reached the desired temperature.
The Test:
Whichever method you choose, test the chocolate before using it to make sure it doesn't need a little more time to become tempered. Drizzle a bit on a smooth, cool surface and wait. If it doesn't set up shiny and hard in 3 minutes, it's not tempered yet. Keep stirring or add a big additional hunk of seed chocolate. After a few minutes test again. When the overall batch is finally tempered, part of the added seed chocolate may remain unmelted. Remove and save it for another day.
-- Danielle Centoni
http://www.oregonlive.com/foodday/oregonian/index.ssf?/base/living/1201899312226870.xml&coll=7
