As a beginning homebrewer, you have most likely started out brewing using a kit that comes with instructions or at least a recipe you were given or found online. Depending on the beer style you are brewing, you are likely instructed to add one or more hop varieties at different times during the beer making process, usually during the boil. In case you have wondered why hop A is to be added at the beginning of your boil and hop B is to be added during the last 10 minutes of the boil, this “Did-You-Know” is for you.
Much like following a cooking recipe for your favorite meal, what you add to the kettle and at what stage of the process depends on what you want the finished product to taste and smell like. Most beer styles will require at least one, often more, additions of hops during the boil, and each of those additions is done on purpose to achieve a desired result in the beer profile.
You can research this topic exhaustively and you will find whole scholarly papers on the subject. But the “Cliff’s Notes” basics on hop additions boil down (pun intended!) to the following simple guidelines:
Early hop additions (those that you add at the beginning of a 60 minute boil, for instance) are meant to add base bitterness to the beer. Most all beer styles, even the ones that are not thought of as “bitter beer”, require at least some minimal level of hop derived bitterness, to balance the sweetness from the malt sugars and the “heat” from the alcohol. Without that bitterness being present, the beer would likely be unpleasantly sweet or “alcohol-y”. Some beer styles, like a classic West Coast IPA typically make heavy use of early hop additions to create their characteristic clean hop bitterness up front. How much bitterness you get will depend on the hop variety, the alpha acids it contains (this is typically data shown on the package the hops came in), and the total amount of time the hops remained in the boil. By boiling these hops a long time, you maximize their contributions to bitterness, but you are also losing most if not all of those hops’ ability to contribute flavor and aroma profiles to your beer, as these tend to “boil off” the wort during a long boil.
Any recipe that calls for hop additions in the middle of the boil, say anywhere from 45 to 20 minutes before the end of the boil, is using these hops as “flavor” hops. Yes, you will still get some bitterness since you are afterall boiling them, but more importantly, you will get some of the hop flavor compounds to survive the boil and get into your beer. You will still lose most of the more volatile aroma compounds.
Late hop additions during the last 5-10 minutes of the boil (and even after the boil ends) are called “aroma” additions. The short time in the hot wort will still impart some small levels of hop bitterness and flavor, but most importantly, most of the aromatic hop compounds will survive into the finished beer, giving off the hop aroma so characteristic of some beer styles.
So now that you know, start experimenting with different hop varieties and kettle times!