Further investigation of the roaster told the whole story about the end product.
The two beans seen on the picture were found in the drum after the roast was performed. They were actually almost glued to the drum and have certainly a longer history in the roaster then the beans I was preparing this evening.
It is incredible that two small beans can destroy a whole batch consisting of thousands of beans!
Here the roaster have been properly cleaned and is now ready for new tasks. I am really looking forward to get my next shipment of beans. They are currently crossing the Atlantic while I have to settle with my smoke-roasted beans in the meantime..