One of the qualities that stands out between different styles of beer is the bitterness of the beer. This can be measured in IBU’s or International bittering units. The IBU measurement goes from 0 IBU’s or a beer that has no noticeable bitterness like a fruit based beer to 120 IBU’s which is like a strong Imperial IPA. And of course that bitter flavor comes from the hops you add to your beer.
But it is what’s inside the hops that really makes the bitter flavor. Alpha acids are present in all hop varieties. The more alpha acids the more bittering potential that hop has and the higher IBU’s you can attain. Just because you used a hop in your brew doesn’t mean that you will achieve the bitterness that your hops could bring. It depends on when you add a hop to the boil and how much of the alpha acids are extracted from the beer. Beersmith is one of the best brewing software tools out there and can calculate the IBU’s in your beer before you even start brewing.
In general a 60 min brew will extract most of the alpha acids from a hop but there are beers out that even use 90 min boils to extract even more. Keep in mind though that these long boils will generally lose any of the flavor and aroma from the hops. Hops added in the begging of a brew or 30-60 left in the brew are generally called your bittering hops. These are the hops that are meant to mostly contribute to the bitterness off the beer. Standard bittering hops that I have used are cascade hops. These are a hop used widely in the beer world though many including myself are now looking for more exotic hops for their unique bittering ability.
The next hop addition zone is flavoring hops. These hop additions can generally take place between 10 and 40 min. There are many variations of flavor you can get from hops like, herbal grassy notes, citrusy notes, or even floral flavors. If hops are boiled too long you can lose flavor and if you do not boil enough you may never gain it. Keep this in mind when deciding how you want your beer to taste. Hops that I like to use for flavoring are Fuggle hops. These have a nice citrus and floral flavor along with a hint of herbal. They have worked well in many beers I have made.
The last hop addition category is aroma hops. These hops are generally added in the last 15 min of your boil. The purpose is to attain the aroma of the hop in your beer. This is the easiest flavor to predict in your beer because the aroma you will get in your beer will closely match that of the hop. You can also achieve hop aroma by dry hopping or adding hops to your fermentation. My favorite aroma hop has to be Citra hops. This hop has very floral and citrus notes and can also be a good flavoring hop if you would like a citrusy flavor in your beer.
Now you probably noticed that these categories overlap. This means that you can use a hop for dual purposes. Add a hop at 12 minutes to get some flavor and some aroma or ad one at 35 minutes to a little more bitter from your flavoring hop. It’s all up to you. Try different hops and addition times and note the results. This will make you a better and more knowledgeable brewer.