As I live inside the EU, I am not so familiar with the procedure, but I know that on german airports, the VAT refund is handled by Global Refund. But they only handle special cheques given out by shops that take part in the "Tax Free Shopping" - system. And I think only shops that have a lot of foreign tourists do take part in this system. So with the general receipts, things will get a little tricky. You might get a refund directly from the German customs, but I do not know how much paper work you need to fill out for that. Sorry that I can't help you more, but you might find some more information on the webpage mentioned above.

Cheers, Stefan