Part of the Barley plant and...
'Hops, a minor ingredient in beer, are used for their bittering, flavoring, and aroma-enhancing powers. Hops also have pronounced bacteriostatic activity that inhibits the growth of Gram-positive bacteria in the finished beer and, when in high enough concentrations, aids in precipitation of proteins.'
Oh and I have to say Chocolate Milkshake, though I very rarely get to drink it.