Korpiklaani, the Finnish folk-metal band that started in 1993 under the name of Shaman, and changed their name in 2002 to Korpiklaani (Clan of the wilderness).
Their music consists of metal with a happy folky base. So does their choice of instruments, they use a mixture of electric guitars and drums as well as violin, woodwinds, jouhikko, djembé, and the typical Finnish folk instrument: the accordion. They reject synthesizers (of course), and use only genuine instruments.
To most people their music is so cheerful and lively that they cannot resist dancing, laughing and feeling happy. Maybe that is why fans call it 'beer-metal' (it certainly has the same effect as beer), but it could be also due to the many songs about this all-time favorite drink of Korpiklaani.