Hop Aroma Therapy
Remember the last time you had a fresh draft IPA or opened a bottle of pale ale and the floral, herbaceous, sometimes spicy aroma of hops smacked your olfactory nerves? The ability to create varying flavors, aromas, and characters in beer is a great aspect of brewing. And let’s be honest: Most of us love hops.
Hops are the signatures on the paintings that identify our beers. We love the bitterness, but we are constantly hunting the more elusive nuances of aroma and flavor that make our beer unique from batch to batch, style to style. So how do we achieve that perfect balance, trap all that delicious aroma into a bottle, and manipulate it to just the right degree?
What Are Hops?
The hop plant is a vine, and the hop cone, or flower, of the vine is used in brewing. The hop cones brewers use are always female because only the female cones contain significant quantities of lupulin glands. Lupulin glands are small yellow sacks at the base of the cone’s petals that contain the acids and oils that give beer its bitterness and aroma.
All hops contain both acids and oils, though different varieties contain different ratios of acid to oil. Acids, specifically the alpha acids, are the compounds that lend bitterness to beer. Oils, on the other hand, lend the aroma.
Hops that contain relatively high proportions of alpha acids, therefore, are generally used as bittering hops, while hops with a lower percentage of alpha acids and more oils are used as flavoring or aroma hops.
It is the way in which hops are used in the brewing process that dictates the final bitterness and aroma of the beer. Hop acids, for example, need to be isomerized in order to impart bitterness. Isomerization is a chemical reaction that dissolves the acids into a solution (wort) and rearranges the molecules so that they stay dissolved.
In brewing this chemical change is achieved through prolonged boiling. Hop oils, on the other hand, are extremely volatile, which means that they dissipate quickly in the steam of a kettle. Therefore, hop aroma needs to be captured delicately, and there are several strategies for doing so. Before choosing a strategy, however, it’s important to understand the differences between whole hops and hop pellets.
Cones versus Pellets
At harvest time hop cones are either hand picked or stripped from the vine by machine. The cones are then dried and baled together for sale. Hop pellets are made from the dried hop cones, which are ground into a powder and then pressed into pellets. The process of grinding the hops ruptures the lupulin glands, so the stickiness of the hop acids and oils naturally holds the pellets together.
There is very little physical difference, therefore, between whole hops and hop pellets, though there is a degree of practical difference. Hop
pellets have the advantage of being much more compact and therefore easier to store.
They are almost always the packaging of choice for American microbreweries for this reason. Because the powder breaks apart in the boil, no straining from the kettle is necessary and this, again, is an advantage.
Whole hops will rely on the heat and agitation of the boil to release the acid and oil resins, but because the lupulin glands of pelletized hops have already been ruptured, the acids and oils can more quickly and easily dissolve into solution. This may be an advantage in trying to capture aroma at the end of or after the boil.
The process of grinding and pelletizing, however, does give off some heat, and some believe this may change or destroy some of the acids and oils present in the hops. So purists will stick with whole hops, although with modern methods, pellets are probably of equal quality, are easier to use, and stay fresher longer. For homebrewers the choice is one of personal preference.
Using Hops
Hops are a natural preservative, and that was perhaps the first consideration in the advent of their use in beer. Brewers would have quickly discovered, as well, the wonderful balancing effect that the bitter taste and aroma of the hop had on the sweet malt.
Flavor combines the experiences of sense of smell and taste together much in the same way we experience and enjoy the foods we eat as a dual taste/aroma sensation.
Aroma stands alone as an olfactory sensation divorced from the experience of taste.
Both of these characteristics can be controlled individually through specific methods in the brewhouse. These methods include: late kettle hop additions, whirlpool or steeping additions, use of the hop back, dry hopping, and use of hop oils and teas.
Late Kettle Hopping
Late kettle hopping, also called flavor hopping or finish hopping, consists of adding hops in the last few minutes of the boil so that hop oils are dissolved and very little or no isomerization of hop acids (and no bittering) occurs.
Many brewers add bittering hops at the beginning of the boil, flavoring hops about half way, and then finishing hops. As mentioned earlier, hop oils that are responsible for aroma are extremely volatile and will be driven off in the steam of your boil almost immediately. Therefore, a hop addition in the middle of the boil will add some bitterness, probably no aroma, and be more costly for you. Calculate all your bittering hops to be added at the start of the boil. You’ll use fewer hops and can reserve the fine tuning of flavor for the last five to 10 minutes.
The addition of an aroma hop during the last five to 10 minutes of the boil should contribute a significant amount of hop flavor while minimizing the addition of any bitterness. Hop pellets will dissolve more quickly into a boiling wort and the extraction of oils will therefore be more efficient than with whole hops.
Because the contact time with boiling wort is short, a greater amount of hops (1.5 to two ounces) can be used in the last few minutes to achieve maximum flavor. The heat from the boil will affect the chemical makeup of the hops, however, and the resulting character will not be the same as the aroma of the fresh, uncooked hops. In any case limit the boil time of late kettle hops to less than 10 minutes.
Whirlpool or Steep Hopping
Many of the best examples of American microbrewed beers with outstanding hop aroma have undergone no more than a whirlpool hop addition. In commercial breweries the whirlpool occurs after the boil is finished. The heat is turned off and the kettle is recirculated in a clockwise motion to centrifuge the hops into a cone that settles on the bottom of the kettle.
There are two key elements to this stage of the process: The wort is kept covered, and it is no longer agitated by boiling. Some of the beers with the greatest hop aroma made today have seen no dry hopping but rather have undergone liberal additions of whirlpool hops.
In the homebrewery the setup is the same. After the heat to the kettle has been turned off, a generous amount of hops is added to the kettle. The wort is then stirred rapidly for a minute or so, covered, and allowed to stand for about 20 minutes. The covered kettle will trap more volatiles in the wort and the lack of agitation will be more gentle to the hop oils. Again, heat will still change the chemical makeup of the hop, and a unique flavor will result.
If you use an immersion chiller, hop flavor will continue to be extracted for the duration of the 20- to 40-minute chilling time.
The Hop Back
A hop back is nothing more than a strainer that was used in days of old to separate the whole hops in the kettle from the sweet wort running into the fermenter. At some point brewers discovered that adding fresh whole hops to the hop back first and then straining boiling wort through them accomplished two things. First, it acted as a filter bed, straining out the hops and trub, and second, it imparted a fresh hop aroma.
In the homebrewery this method is effective if you are straining boiling wort into a fermenter filled with cold water or using a counterflow chiller to cool your wort. In an open straining system the hot wort flowing over the hops carries oils into the wort, though some of the volatiles will be lost to the open air.
The system is most effective when used in conjunction with a counterflow chiller and constructed so that the hop back is sealed, allowing hot wort from the kettle to flow through it on the way to the chiller without allowing any of the volatiles to escape. It has little practical use in an immersion chiller system.
In general a hop back will be a bit more time consuming, costly, and messy, but it can impart a very close-to-fresh hop aroma.
Dry Hopping
Dry hopping is perhaps the most widely used and most talked about method of adding fresh hop aroma to beer. In principle the method involves adding a quantity of whole or pelletized fresh hops in a straining bag to the secondary fermentation of the brew.
Because the secondary fermentation will be taking place at room or cellar temperature, the chemistry of the hops is not altered or affected by heat. Therefore, the aromatic oils can be slowly extracted from the hops, and the delicate volatiles will not escape. Again, a liberal amount of hops should be used to achieve a full aroma (about two ounces in a five-gallon batch).
For those who employ kegging systems, add the hops at kegging time and allow them to steep for a few weeks before the beer is served. This is the most traditional way of dry hopping and will produce the best results.
If you bottle your beer, you should employ a secondary fermentation for at least a week (two is better) to fully extract the hop aroma before bottling.
Dry hopping during the primary fermentation is possible, but it should only be done when the primary fermentation has subsided (after three or four days) so that the volatiles will not be carried off in the escaping carbon dioxide of fermentation. In any case, secure the hops in a straining bag and weight the bag so that they are fully submerged in the beer.
Proper dry-hop aroma will take some time to develop, and the aroma should continue to improve for months in the keg. Dry hopping, as seen by the success of the first well-traveled and generously dry-hopped India pale ales, also has a great preservative effect on beer. And because fermented beer is an environment hostile to bacteria, don’t worry about contamination from unsterilized hops; it is highly unlikely to occur.
While many beers are late-kettle or whirlpool hopped and not dry hopped, most dry-hopped beers have also seen late kettle and/or whirlpool hopping. The fresh hop aroma of dry-hopped beer seems to be complemented by the flavor quality of late hopping.
Hop Oils and Teas
Isolated hop oils are also available to the homebrewer. Using a carbon dioxide extraction process, manufacturers are able to provide pure, liquid hop oils that can be added directly to the secondary fermenter or keg to produce a calculated amount of hop aroma. Extracted hop oils need to be diluted into extremely small amounts and therefore are difficult for homebrewers to use.
There are also products on the market called late hop essences. Manufacturers of these products have isolated the individual compounds of the oils that give the distinctive late kettle hopping or whirlpool flavor. These are easier for homebrewers to use than the aroma oils.
Hop teas also provide some of the flavor associated with late kettle and whirlpool hopping. Bring a quart of water to a boil in a saucepan, add a generous amount of aroma hops, stir well, turn off the heat, and allowthe hops to steep for about 20 minutes. You can strain this hop tea directly into the secondary fermentation, keg, or simply make the tea when you are preparing your priming sugar and add it directly to the bottling bucket.
Capturing the perfect balance of hop aroma and flavor in your beer will depend on the style and gravity of the beer you are brewing, the brewing method you use, and of course the type and variety of hop. Certain aroma hops, Cascade for example, have become the defining aroma hops in American pale ales.
There are many hop varieties to choose from, and they all have subtly different, wonderful properties. Do some controlled experimentation. You will be rewarded upon opening your next bottle of homebrew with the same tingly sensation you get when smelling freshly cut grass for the first time in the spring.
