Dry hopping is a process used by homebrewers and commercial brewers to add hop flavours and aroma to a beer, which is usually carried out by putting an amount of hops into the brew usually at the end of the primary fermentation, although there are other methods available e.g. directly into the cask. Dry hopping is distinct from hops usually added in the boil for bittering. It seems to have become more popular in recent years with the advent of American style beers some of which use prodigious amounts of hops in the fermentation process. Pre hopped liquid malt homebrew beer kits can be greatly improved by a simple dry hop since the process will replace some of the hop profile lost when the kit was originally manufactured, and some premium kits do include hops for dry hopping to address this. Some hop types are better than others for dry hopping and for late boil additions, although some are dual purpose where they can be used for bittering as well. Clibit's guide on hops http://www.thehomebrewforum.co.uk/sh...777#post483777 and this link http://beerlegends.com/hops-varieties are two of many useful sources of information on hop selection. Typically Goldings and Styrian Goldings are often used to dry hop British style beers, whereas Centennial and Cascade are often used in American beers, although many other hop types are suitable. Hops usually come as flowers or in pellet form. Pellets are ground up flowers compressed into pellets. Pellets are probably better than flowers for dry hopping since when they are immersed in a liquid they break up and the hop particles present a large surface area to give up their flavour and aroma. Note that hop pellets do not dissolve, they simply break up. And hops are naturally sterile so there is little danger of infection when they are directly put in the brew. To dry hop a beer:- - Decide on the hop type or types to be used. There is no rule about what you can add, experiment when you have done a few dry hopped beers. - Decide the weight of your dry hop, the choice is extremely varied from say 25g to 100g plus for a 23 litre brew. It all depends on the style of beer and your personal taste. - Dry hop at the end of the primary fermentation when the CO2 bubble rate has dropped to virtually nothing and cannot strip out the volatile hop oils from the brew, which is mainly what the dry hop process adds to the brew. - Decide whether you are going to chuck the hops in as they are, or use a muslin or nylon bag with or without weights to contain the hops. 'As they are' may mean you have to filter out the hop particles when you bottle or keg, but bags can restrict how the hops give up their flavour and aroma. If you use a bag make sure it it sanitised; boiling before and after use is one way. And bigger bags are better than small bags since they allow the hops to distribute better in the brew. At the beginning of the dry hop period you could also swirl the brew from time to time to move the hop particles around and keep them distributed. - Decide how long the hops will be in your brew. Four to seven days is usual; less than this and the hops won't have been given the best opportunity to work, too long and you may get unwanted flavours being leached out into the brew. - Choose where the brew is stored for the dry hopping period. Warmer temperatures will generally be better than colder temperatures. As an example Brew Dog in their DIY recipe book say that 14*C gives the most aromatic hop profile for their Punk IPA.