Sure bittering hops are added during the boil, and aromatic hops are added towards the end of the boil, but If you want your beer to have that really enhanced hoppy aroma dry hopping is the way to go!
Adding hops near the end of the boil for aromatic qualities may lead to the loss of the aromatic oils due to the inherent harsh nature of the boil so dry hopping is a great way to really enhance the hoppy aroma. By adding hops to the secondary fermenter or keg (or cask) the hops are able to bask in the near finished beer and release their delicate oils to impart their wonderful flavour into the beer. This process can take anywhere from a few days to a few weeks depending on the desired outcome.
Brewers use hop plugs, hop pellets and even whole leaf hops to dry hop their beer. By the time the beer is in the secondary fermenter or keg (or cask) there is sufficient alcohol present to prevent any bacteria (which may be present on the fresh whole leaf hops) from contaminating the beer. Sometimes a mesh bag is used to contain the hops to make it easier for clean up and to prevent blockages in the keg but simply tossing them in is a very common and acceptable method. The homebrewer typically brews 5 gallon batches and it is said that 2 oz of hops is at the high-end of moderate dry hopping, and 4 oz is at the high-end for the hopheads.
Since the objective of dry hopping is to provide additional aromatic properties to the beer aromatic hops are the best choice. These hops have a relatively low alpha acid content (under 6%) and more aromatic hop oils. Goldings, cascade, saaz, and fuggles are just a few of the varieties suitable for dry hopping. It is also important to ensure the hops used for dry hopping are suitable for the beer being made. For example saaz hops would be suitable for dry hopping pilsners or European lagers, and Cascade suitable for an American pale ale. In theory you can dry hop any beer but the purpose of dry hopping is to enhance the hop properties of already hoppy beers. India pale ales, American pale ales and pilsners are good examples of the types of beers ideal for dry hopping. This site notes hop varieties including alpha acid percentage and style of beer commonly used in.
A few local examples of dry hopped beers include Granite Best Bitter Special, Great Lakes Lackeys Caskey and Flying Monkeys Smash Bomb Atomic IPA.
Oh yeah, why is it called ‘dry’ hopping? Since once the hops hit the beer they get wet, right? The ‘dry’ adjective indicates that the hops have not been boiled and are uncooked.
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