Dry hopping is a technique used to develop more aroma and flavour in a beer, especially those with a good hoppy bite such as an IPA and some pale ales. You will find that with a lot of kit beers that include dry hop additions you are advised to add the hops about three days before bottling. This is so that the flavour and aroma of the hop is not ruined by primary fermentation as the production of Co2 and the activity of the ferment destroys some of the hop aroma. The hop aroma is also lost in the boil as this environment is too severe for the aroma to stay intact.
Why Dry Hop?
Dry hopping will add aroma and flavour to your beer and is especially good for IPAs, however it can be done with any type of beer. The aroma from the hops, which is best achieved when dry hopping, improves the overall experience of the drink.
When do I add the hops
Dry hop additions can be added at various stages which achieves a varied level of aroma and flavour, however dry hop additions will never add bitterness, the hops need to be boiled in order for the bitterness to be extracted through the process of isomerisation.
You can add your dry hops during the last 5 to 10 minutes of the boil, this does mean that some of the delicate aroma oils are lost in the boil so for an intense hoppy aroma you would still need to add hops later on.
Some brewers add the hops in the primary fermenter about 3 days before bottling/kegging. This is a method that you'll find with most kit beers that contain a separate hop addition. This will impart aroma, however due to the fermentation process some of the aroma is lost due to the production of Co2 which carries the flavour and aroma away with it.
The secondary fermenter is the most popular option for dry hopping among many brewers. Through this method you can extract the optimum amount of flavour and aroma from the hops. Add the hops for about a week, try not to leave them for too long otherwise you could get an unpleasant grassy aroma/flavour from them.
Some brewers add the hops in the keg however this can lead to a grassy flavour if the hops are left in the keg for too long.
How do I add the hops
Hops can be added loose to the fermenter or in a muslin bag, some say that more flavour and aroma is extracted if added loose however I haven't seen a noticeable difference between the two methods. I prefer to add the hops in a muslin bag and then add it to the brew as this makes less mess when bottling/kegging by containing the hops.
Which Hops Do I Use?
You would usually use hops with a low alpha acid content for dry hopping these include: East Kent Golding, Fuggle, Saaz, Cascade, Williamette and Tettnanger. However you can use whatever hops you like, it's up to you.
Pellets or leaf
You can use both but pellets work quite well when dry hopping. Pellets are often used in commercial brewing and are generally far more convenient to use than leaf hops. If you are using leaf hops don't worry about sanitising them as the alcohol in the beer will kill any bacteria that may be on them. Hops are natural preservative and also have antimicrobial properties.
I hope this info helps!