Castoreum is a excretion product of beavers
Castoreum is also known as Beaver and is a dark brown resin-like substance. It has a fairly characteristic scent that is often compared to the scent of musk. Beavers use Castoreum to grease the fur. In the past, Castoreum was used in bitter drinks, nowadays it is used in alternative medicine, perfume and as a flavoring agent. It is becoming less used by the high price. In Castoreum sits salicylic acid, which is also in aspirin, the reason that in former times doctors also used it to fight fever.
The inspection service of value has conducted research into castoreum. Part 1