|What the hop?|
Hops are the the female flowers of the hop plant and in Latin that's Humulus Lupulus. Hops have been used in brewing for over 1,000 years with the first records of their use dating back to 1079 in the Hallertau region of Germany. They are used mainly to flavour beer adding bitterness to balance the sweetness of a beer's malt. They also impart aroma, act as a preservative, have mild anti-bacterial qualities and play a part in the foam quality.
Before hops herbal mixtures were used to add bitterness to beers. It's thought that once people noticed that hopped beers were less prone to spoiling then the herbal mixtures (known as gruit) were abandoned in favour of hops.
When brewing, hops are added to the kettle and boiled with the wort. The longer hops are boiled for the more bitterness they impart and the less aroma. Although hop variety has a role to play in the bitterness/aroma stakes too.
The hop flowers, or cones, contain alpha and beta acids and also essential oils. The essential oils are what give the aromas and the alpha acids the bitterness. You get certain type of hops which are high-alpha and so are very bittering such as Pacific Gem and Green Bullet. Whereas Motueka and Pacifica are aroma hops. There are also hops that are dual purpose, the famous Nelson Sauvin being an example of one of these.
If you ever hear the term "noble hops" that refers to some traditional hop varieties from Europe namely Hallertauer Mittlefruh, Saaz, Spalt and Tettnanger. These hops are low alpha and therefore are high aroma hops.