Hops can also be added to the fermenter to increase the hop aroma in the final beer. This is called “dry hopping” and is best done late in the fermentation cycle. If hops are added while the fermenter is still actively bubbling, then much of the hop aroma will be carried away by the carbon dioxide. It is best to add hops after foaming has slowed or stopped and the beer has gone through the conditioning phase before bottling (usually about half an ounce per 5 gallons). The best way to utilize dry hops is to place them in a secondary fermenter, where they can sit for a few weeks after the beer has been racked off the residue, allowing the volatile oils to diffuse into the beer before bottling. Many homebrewers keep their hops in a nylon mesh bag – a hop bag – to make it easier to remove the hops before bottling. Dry hops lend themselves to many pale ale and lager styles.
When you use dry hops, there is no reason to worry about adding unboiled hops to the fermenter. Infection of hops does not happen.
It is rare for any group of brewers to agree on the best form of hops to use. Each of the common forms has its own advantages and disadvantages. Which form is best for you will depend on where in the brewing process you use hops and may change as your brewing method changes.