Hops 

Hop plants are native to the temperate zones of the northern hemisphere, and are grown worldwide between the 30th and 50th latitudes, north or south. The hop plant is a perennial fast growing plant – 6-8 meter in less than 8 weeks are recorded. Hops are dioecious, which means that the male and female flowers are borne on separate plants. 

Under ideal conditions each hop-vine produce up to 0.9 kg of hop cones a year. The hop cones are the dried fruits of the female hop plant.
Hops are one out of three members of the plant family Cannabinaceae, which includes hemp and cannabis. There are only three recognized species of hops: Humulus Lupulus, Humulus Japonicus and Humulus Yunnanensis. 

Humulus Lupulus is the only species, which contain large amount of resins and oils needed in the art of brewing beer.

The hop cone is made up of a central stem, called a strig. The bracteoles contain the resin producing glands and are protected by the bracts.  At the base of each bracteole is the seed (if any) and the lupulin glands. The lupulin glands are tiny and yellow, filled with the resin containing alpha and beta acids and hop oils, which is of interest to the master brewer. 

Hops are the spice in beer; they not only give the bitter taste and hoppy aroma, but also affect how the head forms. The bitter taste balances elegantly the sweetness from the malt. Hops increase the stability of the beer, potentially giving it a longer shelf life. Hops are e.g. imported from Germany, USA, Czech Republic and United Kingdom.

The hops are to beer, what grapes are to wine; by choosing a specific or a blend of hop varieties the master brewer can control the desired aroma - e.g. pine needles, elderflower, passion fruit or grape fruit - and desired type of bitterness. By choosing a specific hop variety the master brewer also decide how the bitterness is perceived (smooth harsh, astringent, metallic, rounded, lingering/hanging) and how it is felt on the tongue.

Hop cones can be processed into pellets and extract dependent on the need and policy of the brewer. Hops can be added at different stages in the brewing process to impart a stronger or weaker aroma or bitterness. There are many different types of hops, each having its own characteristics.

Some of the most frequently used hops are:

Hallertauer Mittelfrüh – mild German aromatic hops, especially used in classic lagers

Perle – German universal hops with a medium content of alpha acids

Saaz – classical Czech aromatic hops – one of the oldest and most expensive type of aroma hops.

Cascade – American aroma hops, which among other things deliver aromas of elderflower and citrus to the beer

Fuggles – one of the oldest English sorts, which primarily contributes with an exquisite fruity and hoppy aroma

Hallertauer Magnum – typical German bitter hops

Please also look at this page for more hop varieties: www.hopsteiner.com and for some hop aroma notes: www.brewsupplies.com

Final comments:

How much the hops are dominating the aroma of a beer is e.g. depending on the beer style, the malt-composition, the water composition, the use of hops and when the addition is made, and which yeast strain is used.

When comparing bottom-fermenting and top-fermenting beer styles and how much the ingredients and yeast strain is dominating the final aroma of the beer, I would give the following guidelines, with certain reservations:

Jens Eiken, Master Brewer

Illustrations and part of the text is from Hopsteiner (S.S.Steiner Inc.)