No question that beer is the way to go here. I'll offer one that goes great with brats and leans a bit away from the standard "beer". An outfit in Canada called Unibroue makes an ale they call Ephemere. It is brewed on lees with an apple wort. They recommend it as an appertif but I think the subtle apple flavor plays beautifully off the brats. If you live in the North East it is widely available. I'm not so sure about out West.