When the boil has stabilized, then the first addition of hops can be put in. These are the “boiling” hops or “bittering” hops, and it is from this point that we begin measuring the time of the boil. This hop addition will be boiled a total of 60 minutes.
After 45 minutes of boiling the wort, the “flavor” hops are added. These will be boiled for 15 minutes, and these hops add hop flavor to the finished beer.
Along with the flavoring hops, Irish moss is added. This is because the Irish moss should boil for 15 minutes as well in order to kill any bacteria that may exist in it. Irish moss aids in clarifying the finished beer.
Finally, the “aroma” hops are added at the end of the 60 minute boil directly after the heat has been turned off. Hops that are not boiled long add a floral hop aroma to the finished beer.