Part II: The Care and Feeding of Hops in the Brewhouse
Originially Published By Don Put (Brewing Techniques, Volume 4, Number 3)
The practical application of hops in home brewing requires a basic understanding of how they add bitterness, flavor, and aroma to finished beer. The best beers are crafted by brewers who know when to add them and how to remove them.
The previous installment of Home Brewery Basics discussed the hop plant’s botanical background, structure, essential brewing components, and commercial forms and freshness evaluation for home brewers. This installment focuses on the use of hops in your home brewhouse to get the most out of the form and variety you’ve chosen.
Hops can be added to the brew kettle at any time during wort boiling, but they are usually added at fairly specific times, depending on whether you want to take advantage of their bittering, flavor, or aroma properties. This article examines each of these boil times and explores the mechanical aspects of dealing with hops during each stage of the brewing process.
Hop varieties are loosely classified as either bittering or aroma (see Table I), though some confusion can result if you don’t approach this distinction with some flexibility. Hops known for their bittering properties typically have higher alpha-acid levels (approximately 8% and above) compared with those used for aroma and flavor additions. (For a detailed explanation of hop alpha-acids, see last issue’s installment [March/April 1996, pp. 12–19].) Most bittering hops are not used for later additions, where the brewer wants the finer, more delicate characteristics of the hops to shine through. (Traditionally, bittering hops have been associated with high levels of cohumulone, an alpha-acid linked to “coarser” bitterness.) On the other hand, aroma hops, with low- to mid-alpha-acid levels (8% and below), can be used for bittering without any problems. You will have to use more of them to get the desired bitterness level, but some brewers prefer the mellower bitterness they impart.
As in other areas of brewing, however, exceptions to the rule can be found. The Columbus hop, a recently introduced high-alpha variety, displays desirable properties for both bittering and aroma. Use the table and suggestions as a guideline; let your palette be the final judge. Whatever you do, don’t be afraid to experiment.
Don Put has been an avid brewer since he heard the airlock bubble on his first batch of beer. When he is not brewing with or tweaking his ½-bbl system, he writes fiction, teaches creative writing at Idyllwild Arts Academy, reads any brewing texts he can get his hands on, and spends a great deal of time enjoying the small mountain community of Idyllwild, California, where he lives and brews. He can be reached through the internet at dput@cello.gina.calstate.edu.
Bittering Additions
Numerous factors affect the amount of bitterness that ends up in the finished beer. These factors can be roughly divided into boil or kettle reactions and post-boil handling. The alpha-acid conversion that takes place during the boil is linked to the form of hop used (whole, pellet, or plug), the duration of hop contact time in the boil, the agitation in the boil (is it a good rolling boil or an exaggerated simmer?), and the volume, pH, and specific gravity of the wort. Postboil factors include the amount of time the hops remain in the hot wort, agitation of the hot wort (which should be kept to an absolute minimum to avoid hot-side aeration), and fermentation losses that result from the adsorption of hop bitterness by the yeast cells. Some bitterness is lost when the initial kräusen forms and is either skimmed off or ends up stuck to the side of the fermentor (See “When Fermentation Rears Its Dirty Head” on page 50 of this issue for more information on bitterness losses from kräusen removal). Fermentation losses are the reason your postboil wort always seems a lot more bitter than the finished beer (if you haven’t tasted this difference yet, I highly suggest you try it; you’ll be amazed).
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Table I: Hop Varieties |
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Bittering* |
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Aroma |
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Brewer’s Gold |
Cascade |
Liberty |
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Bullion |
Challenger |
Lublin |
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Centennial |
Columbus |
Mt. Hood |
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Challenger |
Crystal |
NZ Hallertauer Aroma |
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Chinook |
East Kent Goldings |
Progress |
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Cluster |
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Saaz |
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Columbus |
Ultra |
Spalt |
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Eroica |
Fuggles |
Strisselspalt |
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Galena |
Hallertauer |
Styrian Goldings |
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Northern Brewer |
Hersbrucker |
Tettnang |
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Nugget |
Hallertauer Mittelfrüh |
Willamette |
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Perle |
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Pride of Ringwood |
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Progress |
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*Traditionally, these hops have been classified as bittering hops only. The adventuresome nature of brewers, however, has led to experimentation and favorable results using these hops for their aroma quality. |
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During the boil, alpha-acids are isomerized to iso-alpha-acid, which is significantly more bitter than alpha-acid in its unconverted state (see the previous installment for an explanation of isomerization). The greatest extraction and conversion of alpha-acid occurs with boil times between 60 and 90 minutes, with 90 minutes being close to the ideal time. Longer boil times — say 120 minutes — can yield slight gains in conversion, but the gains are small and usually not worth the extra bother. Any differences in extraction can be easily made up by adjusting the amount of hops added, so the amount of time the “bittering” hops are in contact with the boiling wort falls into the realm of brewer’s preference, with one caveat — bittering hops should be boiled for a minimum of 60 minutes. This is one of the reasons that extract brewers usually boil their worts for an hour.
Hop pellets offer up their alpha-acid more readily because the lupulin glands, which carry the alpha-acid, are ruptured during processing. As a result, pellet hop charges can usually be about 10% less for a recipe that specifies whole or plug hops. Pellets also shorten the required boil time (to approximately 45 minutes minimum).
In whole and plug forms, the hops’ lupulin glands are relatively intact, so something must happen in the boil to make sure that the lupulin glands burst, thus liberating the alpha-acid. This is where the vigor of the boil comes into play. A strong, rolling boil is important for many reasons, no matter which hop form is being used, but when using whole hops the rolling boil is essential because it provides the necessary lupulin-gland–bursting agitation. Once the alpha-acid is freed, heat and time facilitate the conversion to iso-alpha-acid.
In general, larger wort volumes yield increased hop utilization in the boil. Thinner worts (lower specific gravity worts) also increase utilization; as specific gravity increases, hop utilization decreases. Wort pH also affects utilization, but pH is beyond the scope of this article.
One of the more challenging aspects of the hop’s magic is its dramatic reaction with boiling wort at first contact. To help prevent boilovers, some brewers prefer to add the charge of bittering hops just before the wort comes to a boil. Others wait until the wort comes to a boil; they then either add the hops slowly or turn the heat down, add the hops, stir them in, and then turn the heat back up. The choice is up to the brewer; either way works well, as long as the length of time the hops are in contact with the boiling wort is taken into consideration (more on this later). You may want to experiment with each method to see which one works best for your brewing setup.
Finish Hops
Finish hops are added 0–30 minutes before the end of the boil. All hops added to the boil contribute to the overall bitterness in beer, although the amount of alpha-acid utilization drops with shorter contact times. Late hop additions impart flavor and aroma qualities — “hop character” — in addition to bitterness. The closer to the end of the boil the additions are made, the more the brewer can emphasize the flavor or aroma aspects of the selected hop variety. Finish hopping, therefore, can involve more than one hop addition.
Flavor aspects are harder to define and describe and are definitely more subjectively experienced than bitterness, but they exist nonetheless. Hops added 15–30 minutes before the end of the boil usually contribute little aroma to the beer because the volatile aromatic elements of the essential oils evaporate rather quickly. Some of these compounds, however, undergo temperature-induced changes and survive into the finished beer, affecting its flavor profile. Remember, hops make many subtle contributions to the overall taste of the finished beer, and many of these contributions are at best only vaguely understood.
Aroma hop additions can be divided into two groups, depending on the temperature of the wort. Hop additions made within 10 minutes of the end of the boil or after the end of the boil, and hop additions made after primary fermentation (commonly called dry hopping). Dry hopping can be done during secondary fermentation or in the keg. Whether the hops are added before knockout or in the fermentor, both methods are designed to give the beer a strong hop nose, though they don’t necessarily give identical results.
Late-boil additions: The closer to knockout the aroma additions are made, the greater the odds that their varietal bouquet will end up in the finished beer. I’ve had the best luck with additions made within 5 minutes of the end of the boil, followed by a steeping for about 10 minutes. These additions give a different aroma than if the same hop were used for dry hopping. Even a short exposure to the hot wort causes chemical reactions that tend to remove some of the initial harsh piney or resiny aromas and tastes that can result during some stages of dry hopping. Even though late charges will contribute some bitterness, it will be negligible in the overall scheme of things.
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Calculating Bitterness |
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Numerous formulas of varying complexity are currently available for calculating the bittering potential for any given hop charge (references 1, 2, 3, and 4, or reference 5 for a summary of each). These formulas attempt to quantify the level of hop utilization — the amount of alpha-acid converted and the resultant bitterness — for a charge of hops with a certain alpha-acid percentage. One of the main differences between the formulas is the degree of utilization ascribed to various boil times. Do the differences between the various formulas mean that they are essentially useless? Not at all. For home brewers, the important thing is to achieve your goals in the beer you are brewing. The formulas give you reasonable tools for estimating your beers’ bitterness so that if you want to increase or decrease the bitterness in subsequent batches you will have some real numbers with which to work. (The only completely accurate way to measure bitterness is by laboratory analysis. As a practical matter, though, laboratory data would have to be collected for each batch before you could make any meaningful generalizations. Consistency is the key, and a simple calculation method, consistently applied, can be of great practical benefit.) Easy Calculations for Home Brewers The easiest calculations measure hop bitterness in terms of alpha-acid units (AAUs) or homebrew bittering units (HBUs). The more advanced formulas give the result in terms of international bittering units (IBUs), so you can tell something about the measurement method by the units in which the result is given. The interchangeable HBU and AAU measurements are derived by the following simple formula: AAUs (or HBUs) = AA x W where AA is the percent of alpha-acid in the hops, and W is the weight of the hops in ounces. The AAU method of measuring bittering potential has a couple of drawbacks. Batch size is not figured into the equation, and there is no way to adjust the formula to account for the time the hops contact the boiling wort. For the beginning home brewer, however, the formula is a very useful tool. Because the AAU is closely aligned with the normal homebrew batch size of 5 gal, and because most of the bitterness in the finished beer comes from the first hop charge, the AAU formula can get you in the ballpark, especially in beer styles where only one hop charge is the norm and finishing hops are added within 15 minutes of the end of the boil. Though the AAU formula is not nearly as “accurate” — a relative term when trying to estimate bitterness levels in beer — as the more complex IBU formulas, it is convenient and affords beginning brewers the opportunity to get used to applying some simple science to what previously may have been a follow-the-easy-steps process. For the more adventuresome, I suggest checking out the IBU formulas by Jackie Rager and Glenn Tinseth (2,4,5). The AAU formula also makes it easy to work backwards from a recipe that gives only the target AAU value or the hop variety and alpha-acid level of the hops (your hops may differ from those of the recipe). For example, if a recipe calls for 12 AAUs of Northern Brewer for 60 minutes, and you have some 8.7% alpha-acid Northern Brewer hops, you can simply divide the desired AAUs (12) by the alpha-acid rating of the hop (8.7%); in this case, you would know to add about 1.4 oz of your 8.7% Northern Brewer hops to duplicate the AAUs of the original recipe. For a defense of the AAU, a thorough examination of factors affecting utilization, and an examination of one of the factors affecting utilization in Rager’s IBU formula, see “Hop Utilization,” in Dave Miller’s “Ask the Troubleshooter” column in a previous issue of BrewingTechniques (6). A detailed examination of the more complex formulas is beyond the scope of this column; I encourage you, however, to experiment with them as your quest for understanding grows. (The online Hops FAQ compiled by Norm Pyle [5] is an excellent reference — it provides an overview of hops, the various bitterness formulas, and the currently available utilization numbers.) |
Freshness is an important consideration when choosing hops for any boil addition, but it is especially critical for late aroma additions. Experiment with various quantities. An ounce of the freshest aroma hops you can find is a good place to start for a 5-gal batch; adjust from there.
A third method for adding hop aroma — known as first wort hopping — has received a lot of attention in homebrew circles lately. This process, mainly used in Pilsener-style beers, can be considered an aroma addition even though the hops are added as the first runnings from the sparge fill to the kettle. Because this is a relatively new technique in the home brewing community, and one that falls in the domain of advanced brewing techniques, it is outside the scope of this column. At present, the best summary of the technique is available on the World Wide Web at Dave Draper’s page (7). Stay tuned for more coverage in BrewingTechniques.
Steeping hops: Steeping hops is easy if you use an immersion-type chiller or a water bath to cool the wort. For those who use a counterflow chiller, where the wort in the kettle stays at higher temperatures longer, experimentation with steeping-hop additions at regular intervals while chilling may offer interesting results. The longer the aroma hops contact the still-close-to-boiling wort, the greater the chance of losing the delicate aromatic fractions through evaporation. Keep good notes, and don’t be afraid to add quantities that may seem excessive. With bold experimentation, you just might find an ideal aromatic hop addition schedule that fits your taste and procedure. It is really difficult to ruin a beer through large aroma-hop additions (within reason, of course).
Dry hopping: As I mentioned earlier, dry hopping can give a beer an incredibly fresh hop nose. Dry hopping is simply adding hops to the finished beer (½–2 oz for a 5-gal batch is a good start) and allowing sufficient contact time (7–14 days) for the essential aromatic oils to infuse into the beer. The effect is almost as if you’re smelling fresh hops. Just toss them in, using any form of hops — pellets will settle out, whole hops will float — and siphon the beer out from over or under them when it’s time to bottle.
One refinement involves using hop bags to keep the hops from getting loose in the beer. Tight meshes that will contain pellet hops are available.
I’ve had the best luck when dry-hopping in a keg. Because this is a closed system, the effect lasts longer than when I dry hop in a secondary fermentor and transfer the beer to a bottling bucket. No matter how careful you are, some of the aroma is lost during any transfer process, and you risk damaging the delicate aroma constituents through oxidation reactions.
The main question that usually arises is, “How do I keep from infecting my beer if I toss in unsterilized hops?” Although there are no guarantees, finished beer is not a very hospitable environment for most spoiling microorganisms, and hops provide a poor host environment for bacteria to inhabit (remember hops’ preservative qualities). Furthermore, the process has been used successfully for hundreds of years without problems with contamination. I personally have never had a dry-hopped batch of beer go bad. I do take precautions, though, like boiling the hop bags and the stainless steel weights I use to sink the hops to the bottom of the keg to sterilize them before use. But I have never done anything to the hops.
One of the finest beers I ever made was a style that really shouldn’t have been dry hopped, but, hey, that’s what home brewing’s all about. I used ½ oz each of whole, fresh Fuggles and East Kent Goldings. I can still smell the incredible aroma that resulted from the synergistic interaction between the two varieties. About the only downside I have experienced with dry hopping is that it is often hard to get consistent results, and there seems to be a definite time frame required for full effectiveness.
Keeping Hops out of the Fermentor
Whether you use whole or pellet hops, you usually have to devise some way to leave the hops behind when you transfer the hopped wort from the kettle to the fermentor. Hops trap a large amount of the hot break, which can cause off flavors in finished beer. In addition, you risk plugging up the fermentation lock or blowoff tube, if you use these methods.
There are almost as many methods for separating hops from wort as there are home brewers. Most of the methods involve using hop bags, some sort of filter, an extended settling time, whirlpooling, or a combination of these methods.
Hop bags used in the boil can be very effective in preventing siphoning problems during transfer. Fairly wide mesh bags can be used for whole or plug hops, while finer mesh bags are available for containing hop pellets. One thing to keep in mind when using hop bags is that utilization usually suffers a bit, and you should compensate by adding about 10% more to any given hop addition, no matter when it is added in the boil. Also, hops, even pelletized hops, swell quite a bit when they get wet. Therefore, don’t pack the hops so tightly in the bag that they form a pillow. Fill the bag to a maximum of about one-quarter full of dry hops so that the hops are readily saturated.
A simple filter can be made using a copper or stainless steel scrubbing pad (the ones without soap!) and attaching it to the inlet side of your racking cane. I use large stainless steel pads that I buy from restaurant supply stores, but my batch size is usually 17 gal, and that’s a lot of wort to filter.
The pads work pretty well for whole hops, but they are considerably less effective for trapping the smaller pellet particles. For pellets, you can replace the scrubbing pad with a fine-mesh hop bag. Some brewers use a combination of both; they attach the hop bag over the scrubbing pad (this keeps the bag “inflated” and provides more surface area for filtering).
I currently use a combination approach because I have found that it works best for my brewing setup. I attach a filter assembly to the inside of my kettle, but I let the chilled wort stand for 30–45 minutes to allow the hops and trub to settle to the bottom. If I use a high percentage of pellets and get impatient during the settling process, I may use a fine-mesh hop bag on the discharge end of the racking hose and catch any hop particles that may have made it past the primary filter. Of course, if you plan to use filters that have not been immersed in the boil, sanitize them thoroughly along with your siphon hose and racking cane.
Hops: A Fertile Ground
Although it could be argued that the hops’ contribution to beer spills over onto the art side of the brewing process, there is enough science involved to make repeatability possible, even on the homebrew level. Just as fine spices give a good chef the freedom to explore and invent, so do hops provide brewers the opportunity to develop his or her own “hop” style. Home brewing is not only about trying to nail a specific style well; it is also about developing your own style through creative recipes. Each of these goals are admirable for different reasons. It is important to remember that many if not all beer styles developed as the result of brewers experimenting within the constraints imposed by the time period, location, and available ingredients.
Hops form a vital part of many of today’s beer styles, and there are more hop varieties available now than ever before in brewing history. Adventurous home brewers have the opportunity to try many possible varietal combinations in their brews. I encourage you to explore the fertile ground that hops offer.
References
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