Don't confuse the idea of bittering, flavor and aroma hop additions with the common designation of many hops as
for bittering or
for aroma. All hops will provide all three components. How much you get of each one depends on variety and timing. Hops labeled "bittering" were bred to be high in alpha acid with little or no regard to their flavor and aroma. Hops labeled "aroma" are often older varieties, bred and cultivated before the bean counters at large commercial breweries demanded high-alpha hops. In the past couple of decades many "dual use" hops have been released. These high-alpha hops will provide lots of bittering, but also provide a strong aroma.
When hops are boiled, the
alpha acids become isomerized, making them soluble in wort and providing bitterness. This isomerization takes some time, and the "utilization curve," i.e., the graph showing how much bitterness you get from the hops from how long of a boil, starts to level off at just about one hour. So we usually base our hop schedules on a one hour boil. If you boil your hops longer than an hour you
will get more bitterness out of them, but you're in the land of diminishing returns.
Flavor and aroma are sort of two sides of the same coin. They refer to volatile oils that provide all the spicy, floral, fruity and piney notes. Since they are volatile, the longer they are boiled, the less they will be present in the finished beer. Flavor compounds are less volatile, and depending on the variety they can often be detected even after a full hour boil, though obviously at very low levels. So flavor additions to your beer will usually be at 30 minutes or less.
Aroma compounds are the most volatile. We'll put aroma additions in at ten minutes or less. Note that you will still get flavor from boiled aroma additions. If you
dry hop your beer, you will get aroma, with little (if any) flavor. Dry hopping will add
no bitterness to your beer.
Also note that you will get some
bittering from boiled flavor and aroma additions, but of course at lower levels than if you'd boiled them for 60 minutes. Brewing software such as
Beer Smith helps make your bitterness calculations much easier.
Designing hop schedules is the art/craft of balancing the three components that hops brings to beer. Experience, studying recipes and reading will be your guides. Don't be afraid to experiment!
