The Bavarian purity laws defined beer in that part of the world as something that can only have hops, water and wheat.
Hops, water and barley. I think not using wheat was kind of the point actually, since wheat can be made into bread, and you wouldn’t want a bread shortage, would you? Banning others from brewing wheat beers, and then giving a monopoly to your own court brewery to corner the market, is also a baller business move.