Prior to the 1600's in Europe, most beer was spiced with an herbal mixture. These beers are called Gruits. The exact blend of herbs and spices was a closely guarded secret, but commonly used were mugwort, yarrow, cinnamon, nutmeg, and nettles. Mugwort has a mellow sage-like aroma, but it has strong bittering properties and is one of the best herbs aside from hops for this purpose.
From 1/2 to 1 oz. of dried Mugwort for bittering is sufficient for a 5 gallon batch.