It’s because chocolate, in a solid state when you buy it is tempered. This means that liquid chocolate has been cooled to the right temperature and is worked and mixed while it cools to re-align the crystals. This makes the chocolate shiny and gives it that desirable snap.
So how can you do it at home? You’ll need a microwave, a microwaveable dish and a stirring implement like a spatula.
Break the chocolate into chunks and place in your microwaveable dish.
Microwave it for 30 seconds, take it out and stir it. It will still be very solid. Return it the microwave for ten seconds – remove and stir again. Repeat at increments of five seconds until the chocolate is fully liquid BUT (and here’s the catch), you don’t want the chocolate to be warm. It must remain cool whilst liquid to stay tempered and shiny.
Test the temperature each time you remove it from the microwave by touch a bit of the chocolate to your lower lip. It shouldn’t feel hot or cold.
Once it is fully liquid (all lumps have disappeared) and is smooth but cool in temperature, test a little by drizzling a strand onto a metal or cool surface – a plate will suffice. If it sets evenly then congratulations – you’ve tempered chocolate.
If it doesn’t set, throw in a couple of left over pieces of chocolate. Stir for a bit and try the setting again. These pieces can re-introduce the hardening crystals – called ‘seeding’.
Once you’ve checked it and it’s fine use it to decorate cakes, truffles, make cake-pops or cover millionaire’s shortbread and it’ll be shiny and brilliant.