Hops are the female flower cones of the hop plant (Humulus lupulus). They are use primarily as a flavoring and stability agent in beer, and also in other beverages and in herbal medicine. The first documented use in beer is from the eleventh century. Hops contain several characteristics favorable to beer, balancing the sweetness of the malt with bitterness, contributing flowery, citrus, fruity or herbal aromas, and having an antibiotic effect that favors the activity of brewer's yeast over less desirable microorganisms. The hop plant is a vigorous climbing herbaceous perennial, usually grown up strings in a field called a hopfield, hop garden or hop yard. Many different varieties of hops are grown by farmers all around the world, with different types being used for particular styles of beer.