Section 1 – Brewing with Malt Extract
Chapter 5 – Hops
What are They?
Hops are the cone-like strobiles of a climbing vine that is native to the temperate regions of North America, Europe and Asia. The species has separate male and female plants. Only the female vines (known as bines) produce the cones. The vines will climb 20 ft or more up any available support and are commonly trained onto strings or wires when grown commercially. The leaves resemble grape leaves and the cones vaguely resemble pinecones in shape but are light green, thin and papery. At the base of the bracts are the yellow lupulin glands that contain the essential oils and resins that are so prized by brewers for their bittering and aroma qualities.
Hops have been cultivated for use in brewing for over 1000 years. The earliest known cultivation was in Central Europe, and by the early 1500s, cultivation had spread to Western Europe and Great Britain. At the turn of the century, about one dozen varieties of hop were being used for brewing; today, there are over one hundred. The focus of breeding programs has been to increase the alpha acid bittering compounds, while improving yield and disease resistance.
What Do They Do?
Hops are a natural preservative and part of the early use of hops in beer was to help preserve it. This is how one particular style of beer, India Pale Ale, was developed. The popular myth is that at the turn of the 18th century, British brewers began shipping strong ale with lots of hops added to the barrels to preserve it during the several month voyage to India. By journey’s end, the beer had acquired a depth of hop aroma and flavor. Perfect for quenching the thirst of British personnel in the tropics.
[figure 33 – lupulin glands]
Beer, as we know it today, wouldn’t be beer without hops. Hops provide the balance and are the signature flavor in many styles. The bitterness contributed by hops balances the sweetness of the malt sugars and provides a refreshing finish. The main bittering agents are the alpha acid humulone resins, which are insoluble in water and not particularly bitter until isomerized by boiling. The longer the boil, the greater the percentage of isomerization and the more bitter the beer gets. One humulone constituent, called co-humulone is easier to isomerize than the others, but it is also commonly perceived to give a rougher bitterness to the beer. Even though this position is debatable, selection of low co-humulone character was encouraged as new varieties were developed. Many of today’s high-alpha varieties like Magnum and Horizon, have lower co-humulone than older, lower alpha varieties of the past, such as Galena and Cluster.
While most of the bitterness comes from isomerization of the alpha acid resins, the characteristic flavor and aroma compounds come from the essential oils, which are typically 1-2% of the dry weight of the cone. These are volatile and are lost to a large degree during the boil. The light aromatic oils (Myrcene, Linalol, Geraniol, Limonene, Terpineol, etc.), are responsible for the fresh hop aroma you smell when you open the bag, and what you can impart to your beer by dry hopping. The heavier aromatic oils (e.g., Humulene, Caryophyllene, Farnesene) and their oxides/epoxides, are what you smell from the late hop additions to the boil, and it is these aromas as they manifest in the beer that are identified as "noble".
There are many varieties of hops, but they are usually divided into two general categories: bittering and aroma; although today there is a pretty clear-cut group of “dual-use” hops of moderately high bitterness but with good aromatic properties too. Bittering hops are high in alpha acids, at about 10% by weight. Aroma hops are usually lower, around 5% and contribute a more desirable aroma and flavor to the beer. Several hop varieties are in-between and are used for both purposes. Bittering hops, sometimes called kettle hops, are added at the start of the boil and boiled for about an hour. Aroma hops are added towards the end of the boil and are typically boiled for 15 minutes or less. Aroma hops are also referred to as finishing hops. By adding different varieties of hops at different times during the boil, a more complex hop profile can be established that gives the beer a balance of hop bitterness, taste and aroma. Descriptions of the five main types of hop additions and their attributes follow.
For a good discussion of the essential hop oils, see Stan Hieronymus’ book, For the Love of Hops, from Brewer’s Publications (2012).
First Wort Hopping
An old yet recently rediscovered process (at least among homebrewers), first wort hopping (FWH) consists of adding a large portion of the finishing hops to the boil kettle as the wort is received from the lauter tun. As the boil tun fills with wort (which may take a half hour or longer), the hops steep in the hot wort and release their volatile oils and resins. The aromatic oils are normally insoluble and tend to evaporate to a large degree during the boil. By letting the hops steep in the wort prior to the boil, the oils have more time to oxidize to more soluble compounds and a greater percentage are retained during the boil. A blind-tasting among professional German brewers suggested that the use of FWH resulted in a more refined hop aroma, a more uniform bitterness (i.e. no harsh tones), and a more harmonious beer overall compared to an identical beer produced without FWH.
The merits of FWH are hotly debated among brewers. The popular consensus among many seems to be that it really doesn’t contribute to flavor or aroma and the utilization of FWH equates to about a 90 minute boil.
Bittering
The primary use of hops is for bittering. Bittering hop additions are boiled for 45-90 minutes to isomerize the alpha acids; the most common interval being one hour. There is some improvement in the isomerization between 45 and 90 minutes (about 5%), but only a small improvement at longer times (<1%). The aromatic oils of the hops used in the bittering addition(s) tend to boil away, leaving little hop flavor and no aroma. Because of this, high alpha varieties (which commonly have poor aroma characteristics) can be used to provide the bulk of the bitterness without hurting the taste of the beer. If you consider the cost of bittering a beer in terms of the amount of alpha acid per unit weight of hop used, it is more economical to use a half ounce of a high alpha hop rather than 1 or 2 ounces of a low alpha hop. You can save your more expensive (or scarce) aroma hops for flavoring and finishing. See Table 7 for the percent utilization of the hops as a function of boiling time and boil gravity.
Flavoring
By adding the hops midway through the boil, a compromise between isomerization of the alpha acids and evaporation of the aromatics is achieved to yield moderate bitterness and characteristic flavors. These flavoring hop additions are added 40-20 minutes before the end of the boil, with the most common time being 30 minutes. Any hop variety may be used. Usually the lower alpha varieties are chosen, although some high alpha varieties such as Northern Brewer and Challenger have pleasant flavors and are commonly used. Often small amounts (1⁄4–1⁄2 oz, 7-15 g) of several varieties will be combined at this stage to create a more complex character.
Finishing
When hops are added during the final minutes of the boil, less of the aromatic oils are lost to evaporation and more hop aroma is retained. One or more varieties of hop may be used, in amounts varying from 1⁄4–4 oz, depending on the character desired. A total of 1–2 oz. is typical. Finishing hop are typically added 15 minutes or less before the end of the boil, or are added “at knockout” (when the heat is turned off) and allowed to steep ten minutes before the wort is cooled. In some setups, a “hop back” is used—the hot wort is run through a small chamber full of fresh hops before the wort enters a heat exchanger or chiller. A word of caution when adding hops at knockout or using a hop back—depending on several factors, e.g., amount, variety, freshness, etc., the beer may take on a grassy taste, probably due to tannins or other compounds which are usually neutralized by the boil. If short boil times are not yielding the desired hop aroma or a grassy flavor is evident, then I would suggest using FWH or Dry Hopping. High quality, noble hop varieties are your best bet for fine hop aroma character.
Whirlpool Hopping and Hop Steeping
Whirlpool hopping or hop steeping, comes from commercial brewing practice where the wort is directed to a whirlpool after the boil to separate spent hops and trub from the wort before it goes through the plate heat exchanger for chilling. The hot wort will often spend 30–60 minutes in the whirlpool before being chilled, and brewers would use this opportunity to add more hop oil to the wort. The temperature in the whirlpool is hot (>175°F [>80°C]) but not boiling, which prevents a lot of the hop oil from evaporating. It is important to understand that the use of a whirlpool is a necessity for commercial brewers having to separate the trub, but generally not a necessity for homebrewers. Hop steeping is a good way to improve hop flavor and aroma in a beer, but the whirlpool action is not necessary, simply steeping the hops in the hot wort will extract the oils. Some isomerization will also occur at hot temperatures, but it will only be 20-40% of the isomerization that would occur by boiling for the same amount of time as the steep.One drawback to hot steeping is that the beer may take on a grassy taste, due to hop polyphenols that would normally be neutralized by the boil. If the hop character ends up too grassy, then I would suggest using more of your hops in the boil and less in the steep. If there is not enough fresh hop character, then I would suggest using dry hopping.
Dry Hopping
Hops can also be added to the fermentor for increased hop aroma in the final beer. This is called “dry hopping” and is best done late in the fermentation cycle. If the hops are added to the fermentor while it is still actively bubbling, then a lot of the hop aroma will be carried away by the carbon dioxide. It is better to add the hops (usually about a half ounce per 5 gallons) after bubbling has slowed and the beer is going through the maturation phase prior to bottling. The benefit of adding hops at this stage is that the yeast are still active and can take up any oxygen that gets into the wort. On the other hand, the hops oils will adsorb onto the yeast cells, and an appreciable fraction will be taken out of solution when the yeast settle out. The best way to utilize dry hopping is to put the hops in a secondary fermentor or keg, after the beer has been racked away from the trub and let it sit a couple of days to a week before bottling, allowing the volatile oils to diffuse into the beer. The drawback here is that the extended time allows for more hop polyphenols and tannins to leach into the wort, which can give the beer a dry aftertaste, like old tea. Many homebrewers put the hops in a nylon mesh bag—a “hop bag,” to facilitate removing the hops after a couple days.
Many varieties of hop are appropriate for dry hopping, and several varieties can be combined to give the beer a more complex character. While you may be tempted to use a large portion of noble hops in your beer, you need to consider that this will also add a lot for plant material to the beer, which can contribute to tannic/husky flavors. Even though this tannic quality will subside after a few weeks, a lot of craft and microbrewers use higher alpha varieties, like Centennial, Columbus, and Horizon, because high alphas often have higher oil content per pound also, which means less vegetative matter in the tank. Choose your variety with care because some are very citrusy, resiny and/or assertive, and are not appropriate for every beer style.
Don’t worry about adding unboiled hops to the fermentor when you are dry hopping. Hop oils and resins are anti-microbial, so infection and beer spoilage from the hops just doesn’t happen.
Hop Forms – Pellets, Plugs, or Whole
It’s rare for any group of brewers to agree on the best form of hops. Each of the common forms has its own advantages and disadvantages. What form is best for you will depend on where in the brewing process the hops are being used, and will probably change as your brewing methods change. See Figure 34
Whichever form of hops you choose to use, freshness is important. Fresh hops smell fresh, herbal, and spicy, like evergreen needles and have a light green color like freshly mown hay. Old hops or hops that have been mishandled are often oxidized and smell like pungent cheese and may have turned brown. It is beneficial if hop suppliers pack hops in oxygen barrier bags and keep them cold to preserve the freshness and potency. Hops that have been stored warm and/or in non-barrier (thin) plastic bags can easily lose 50% of their bitterness potential in a few months. Most plastics are oxygen permeable; so when buying hops at a homebrew supply store, check to see if the hops are stored in a cooler or freezer and if they are stored in oxygen barrier containers. If you can smell the hops when you open the cooler door, then the hop aroma is leaking out through the packaging and they are not well protected from oxygen. If the stock turnover in the brewshop is high, non-optimum storage conditions may not be a problem. Ask the shop owner if you have any concerns.
Bittering Hop Varieties
Author’s Note: As of 2025, the following lists are very outdated. These varieties are largely still available, but there are dozens of new varieties that are currently more popular. There are new varieties every year, so these lists are included here for posterity.
Name: Brewer’s GoldGrown: UK, USProfile: Blackcurrant, fruity, spicy aroma; Sharp bittering hop.Usage: Bittering for alesAA Range: 8-10%Hop Oil: 2.0-2.4 ml/100gSubstitute: Bullion
Name: ChinookGrown: USProfile: Heavy spicy/piney aroma; Strong versatile bittering hop, cloying in large quantitiesUsage: BitteringExample: Sierra Nevada Celebration Ale, Sierra Nevada StoutAA Range: 12-14%Hop Oil: 1.5-2.5 ml/100gSubstitute: Brewer’s Gold, Nugget, Target
Name: GalenaGrown: USProfile: Strong, clean bittering hop, citrusy aromaUsage: General purpose bitteringExample: The most widely used commercial bittering hop in the US.AA Range: 12-14%Hop Oil: 0.9-1.2 ml/100gSubstitute: Cluster, Northern Brewer, Nugget
Name: MagnumGrown: US, GermanyProfile: Clean bittering hop;Usage: Good general purpose bitteringAA Range: 12-14%Hop Oil: 1.9-2.3 ml/100gSubstitute: Northern Brewer, Perle, Horizon
Name: NewportGrown: USProfile: Strong bittering hop;Usage: New high alpha bittering hop for ales.AA Range: 13-17%Hop Oil: 1.6-3.6 ml/100gSubstitute: Galena, Nugget, Magnum
Name: NuggetGrown: USProfile: Heavy, spicy, herbal aroma; Strong bittering hopUsage: Strong bittering, some aroma usesExample: Sierra Nevada Porter & Bigfoot Ale, Anderson Valley ESBAA Range: 12-14%Hop Oil: 1.7-2.3 ml/100gSubstitute: Galena, Magnum, Columbus
Name: Pacific GemGrown: New ZealandProfile: Pleasant blackberry aroma with woody undertones, good bittering hop;Usage: Widely used bittering hop AA Range: 14-16%Hop Oil: 1.0-2.0 ml/100gSubstitute:
Name: PerleGrown: Germany, USProfile: Pleasant aroma; Slightly spicy, almost minty, bittering hopUsage: General purpose bittering for all lagersExample: Sierra Nevada SummerfestAA Range: 7-9.5%Hop Oil: .7-1.3 ml/100gSubstitute: Northern Brewer, Cluster, TettnangerName: Pride Of Ringwood
Grown: AustraliaProfile: Poor citric aroma; Clean bittering hopUsage: general purpose bitteringExample: Most Australian beers.AA Range: 9-11%Hop Oil: 1.0-2.0 ml/100gSubstitute: Cluster
Name: SimcoeGrown: US Profile: Strong bittering hop, with unique fresh-cut-pine aromaUsage: Bittering and aroma in American Pale ales. AA Range: 12-14%Hop Oil: 2.0-2.5 ml/100gSubstitute:
Name: WarriorGrown: UKProfile: Mild aroma; A clean bittering hop.Usage: Growing acceptance as a good bittering hop for ales. AA Range: 15-17%Hop Oil: 1.0-2.0 ml/100gSubstitute: Nugget, Columbus
Dual Purpose Hop Varieties
Name: AmarilloGrown: USProfile: Floral and citrus, similar to CascadeUsage: Dual purpose bittering and aroma hop for ales.Example: Old Dominion New River Ale, Rockies Mojo India Pale Ale, Hale’s Pale American AleAA Range: 8-11%Hop Oil: 1.5-2.0 ml/100gSubstitute: Cascade, Centennial
Name: CentennialGrown: USProfile: Floral, citrus aroma, often referred to as Super Cascade because of the similarity; A clean bittering hop.Usage: General purpose bittering, aroma, some dry hoppingExample: Sierra Nevada Celebration Ale, Sierra Nevada Bigfoot AleAA Range: 9-11.5%Hop Oil: 1.5-2.3 ml/100gSubstitute: Cascade, Columbus
Name: ChallengerGrown: UKProfile: Medium, fine spicy aroma widely used for English Bitters; A clean bittering hop.Usage: Excellent dual purpose bittering, flavoring, and aroma hop.Example: Full Sail IPA, Butterknowle BitterAA Range: 6-8%Hop Oil: 1.0-1.7 ml/100gSubstitute: Progress, Perle, Northern Brewer, Horizon
Name: ClusterGrown: US, AustraliaProfile: Medium, spicy/floral aroma; Sharp, clean bittering hopUsage: General purpose bittering (Aussie version has a better aroma and is used as finishing hop)Example: Winterhook Christmas AleAA Range: 5.5-8.5%Hop Oil: 0.4-1.0 ml/100gSubstitute: Galena, Northern Brewer
Name: Columbus (aka. Tomahawk)Grown: USProfile: Strong herbal flavor and aroma; Solid, clean bittering hopUsage: Good general purpose bittering and aroma hop, often dryhopped.Example: Anderson Valley IPA, Full Sail Old Boardhead BarleywineAA Range: 13-16%Hop Oil: 1.5-2.5 ml/100gSubstitute: Nugget, Centennial, Chinook, Target,
Name: HorizonGrown: USProfile: Good Floral, spicy aroma; Excellent bittering dual purpose hop when used in the boil.Usage: Bittering and finishing for all ales and lagers.Example: Lagunitas IPAAA Range: 10-14%Hop Oil: 1.5-2.0 ml/100gSubstitute: Northern Brewer, Northdown, Challenger
Name: Northern BrewerGrown: UK, US, Germany (called Hallertauer NB), and other areas (growing region affects profile greatly)Profile: Hallertauer NB has a fine, fragrant aroma; Dual purpose clean bittering hopUsage: Bittering and finishing for a wide variety of beersExample: Old Peculiar (bittering), Anchor Liberty (bittering), Anchor Steam (bittering, flavoring, aroma)AA Range: 7-10%Hop Oil: 1.5-2.0 ml/100gSubstitute: Perle, Horizon
Name: NorthdownGrown: UKProfile: Similar to Northern Brewer, but with a better flavor and aroma than domestic NB; A clean bittering hop.Usage: Dual purpose bittering, flavor and aroma for ales.Example: Fuller’s ESBAA Range: 7-8%Hop Oil: 1.5-2.5 ml/100gSubstitute: Northern Brewer, Target, Horizon
Name: SantiamGrown: USProfile: Floral, slightly spicy, noble characteristics.Usage: Dual purpose bittering and aroma hop for ales.Example: (too new)AA Range: 5-7%Hop Oil: 1.0-1.5 ml/100gSubstitute: Tettnanger, Spalt,
Name: SterlingGrown: USProfile: Herbal, spicy, slight floral and citrus Usage: Dual purpose bittering and aroma hop for ales and lagers.Example: (too new)AA Range: 6-9%Hop Oil: 1.3-1.9 ml/100gSubstitute: Saaz, Mt. Hood
Name: TargetGrown: UKProfile: Strong herbal/floral aroma can be too strong for lagers; A clean bittering hop.Usage: Widely used bittering and flavoring hop for strong ales.Example: Fuller’s Hock, Morrells Strong Country BitterAA Range: 8-10%Hop Oil: 1.6-2.6 ml/100gSubstitute: Northdown, Fuggle, Willamette
Aroma Hop Varieties
The next group are common examples of Aroma hops. Aroma hops can be used for bittering also, and many homebrewers swear by this, claiming a finer, cleaner overall hop profile. I like to use Galena for bittering and save the good stuff for finishing. But making these decisions for yourself is what homebrewing is all about. There is a category of aroma hops, called the “Noble Hops,” that is considered to have the best aroma. These hops are principally four varieties grown in central Europe: Hallertauer Mittelfrüh, Tettnanger Tettnang, Spalter Spalt, and Czech Saaz. The location a hop is grown has a definite impact on the variety’s character, so only a Tettnanger/Spalter hop grown in Tettnang/Spalt is truly noble. There are other varieties that are considered to be Noble-Type, such as Perle, Crystal, Mt. Hood, Liberty, and Santiam. These hops were bred from the noble types and have very similar aroma profiles, having high humulone oil content and low co-humulone alpha acids. Noble hops are considered to be most appropriate for lager styles because the beer and the hops grew up together. This is purely tradition and as a homebrewer you can use whichever hop you like for whatever beer style you want. After all, we are doing this for the fun of it!
Name: British Columbia (BC) GoldingsGrown: CanadaProfile: Earthy, rounded, mild aroma; Spicy flavorUsage: Bittering, finishing, dry hopping for British style ales. Used as a domestic substitute for East Kent Goldings. Not quite as good as EK.AA Range: 4.5-7%Hop Oil: 0.5-1.0 ml/100gSubstitute: EK Goldings
Name: CascadeGrown: USProfile: Strong spicy, floral, citrus (i.e. grapefruit) aroma.Usage: The defining aroma for American style Pale ales. Used for bittering, finishing, and especially dry hopping. Example: Anchor Liberty Ale & Old Foghorn Barleywine, Sierra Nevada Pale AleAA Range: 4.5-8%Hop Oil: 0.8-1.5 ml/100gSubstitute: Centennial
Name: Crystal a.k.a. CJF-HallertauGrown: USProfile: Mild, pleasant, slightly spicy. One of three hops bred as domestic replacements for Hallertauer Mittelfrüh.Usage: Aroma/finishing/flavoringAA Range: 2-5%Hop Oil: 1.0-1.5 ml/100gSubstitute: Hallertauer Mittelfrüh, Hallertauer Hersbrucker, Mount Hood, Liberty
Name: East Kent Goldings (EKG)Grown: UKProfile: Spicy/floral, earthy, rounded, mild aroma; spicy flavorUsage: Bittering, finishing, dry hopping for British style alesExample: Young’s Special London Ale, Samuel Smith’s Pale Ale, Fuller’s ESBAA Range: 4.5-7%Hop Oil: 0.5-1.0 ml/100gSubstitute: BC Goldings, Whitbread Goldings Variety
Name: FugglesGrown: UK, US, and other areasProfile: Mild, soft, grassy, floral aromaUsage: Finishing / dry hopping for all ales, dark lagersExample: Samuel Smith’s Pale Ale, Old Peculiar, Thomas Hardy’s AleAA Range: 3.5-5.5%Hop Oil: 0.7-1.5 ml/100gSubstitute: East Kent Goldings, Willamette, Styrian Goldings
Name: GlacierGrown: USProfile: Excellent earthy, spicy aromaUsage: Aroma hop for ales.Example: (too new)AA Range: 5-6%Hop Oil: 0.5-1.5 ml/100gSubstitute: Willamette, Fuggle, Styrian Goldings
Name: Hallertauer HersbruckerGrown: GermanyProfile: Pleasant, spicy/mild, noble, earthy aromaUsage: Finishing for German style lagersExample: Wheathook Wheaten AleAA Range: 2.5-5%Hop Oil: 0.7-1.3 ml/100gSubstitute: Hallertauer Mittelfrüh, Mt. Hood, Liberty, Crystal
Name: Hallertauer MittelfrühGrown: GermanyProfile: Pleasant, spicy, noble, mild herbal aromaUsage: Finishing for German style lagersExample: Sam Adam’s Boston Lager, Sam Adam’s Boston LightshipAA Range: 3-5%Hop Oil: 0.7-1.3 ml/100gSubstitute: Hallertauer Hersbruck, Mt. Hood, Liberty, Crystal
Name: LibertyGrown: USProfile: Fine, very mild aroma. One of three hops bred as domestic replacements for Hallertauer Mittelfrüh.Usage: Finishing for German style lagersExample: Pete’s Wicked LagerAA Range: 2.5-5%Hop Oil: 0.6-1.2 ml/100gSubstitute: Hallertauer Mittelfrüh, Hallertauer Hersbruck, Mt. Hood, Crystal
Name: Mt. HoodGrown: USProfile: Mild, clean aroma. One of three hops bred as domestic replacements for Hallertauer Mittelfrüh.Usage: Finishing for German style lagersExample: Anderson Valley High Rollers Wheat BeerAA Range: 3.5-8%Hop Oil: 1.0-1.3 ml/100gSubstitute: Hallertauer Mittelfrüh, Hallertauer Hersbrucker, Liberty, Tettnanger
Name: ProgressGrown: UKProfile: Assertive fruity aromaUsage: Widely used for real cask ales.Example: Hobson’s Best Bitter, Mansfield BitterAA Range: 5-6%Hop Oil: 0.6-1.2 ml/100gSubstitute: Fuggles, Whitbread Goldings Variety
Name: SaazGrown: Czech RepublicProfile: Delicate, mild, floral aromaUsage: Finishing for Bohemian style lagersExample: Pilsener UrquellAA Range: 2-5%Hop Oil: 0.5-1.0 ml/100gSubstitute: Tettnanger, Spalt, Sterling
Name: SpaltGrown: Germany/USProfile: Mild, pleasant, slightly spicyUsage: Aroma/finishing/flavoring, some bitteringAA Range: 3-6%Hop Oil: 0.5-1.1 ml/100gSubstitute: Saaz, Tettnanger, Santiam
Name: Styrian GoldingsGrown: Yugoslavia (seedless Fuggles grown in Yugoslavia), also grown in USProfile: Similar to FugglesUsage: Bittering/finishing/dry hopping for a wide variety of beers.Example: Ind Coope’s Burton Ale, Timothy Taylor’s LandlordAA Range: 4.5-7%Hop Oil: 0.5-1.0 ml/100gSubstitute: Fuggles, Willamette
Name: TettnangerGrown: GermanyProfile: Fine, spicy aromaUsage: Finishing for German style beersExample: Gulpener Pilsener, Sam Adam’s Oktoberfest, Anderson Valley ESB, Redhook ESBAA Range: 3-6%Hop Oil: 0.6-1.0 ml/100gSubstitute: Saaz, Spalt
Name: WillametteGrown: USProfile: Mild, spicy, grassy, floral aromaUsage: Finishing / dry hopping for American / British style alesExample: Sierra Nevada Porter, Ballard Bitter, Anderson Valley Boont Amber, Redhook ESBAA Range: 4-7%Hop Oil: 1.0-1.5 ml/100gSubstitute: Fuggles
Name: Whitbread Goldings Variety (WGV)Grown: UKProfile: Flowery, fruity, a cross between Goldings and a Fuggle.Usage: Often combined with other varieties in BittersExample: Whitbread Best BitterAA Range: 4-5%Hop Oil: 0.8-1.2 ml/100gSubstitute: Progress, Fuggles, EKG
Figure 32 - Hops in their native habitat.
Figure 33— Yellow lupulin glands at the base of the hop petals.
Table 6 - Hop Forms and Merits
Figure 34 – hops (top), baled whole hops (left), an hop pellets (right).
(Author's note, 2025: I haven't seen a hop plug in about 30 years.)
Figure 35 – Cascade hops on the vine.
Figure 36 - Weighing hop pellets on an electronic scale.
How to Measure Hops
Alpha Acid Units (AAUs)
As noted in the glossary, there are two ways to measure hops for use in brewing. The first way measures the bittering potential of the hops going into the boil. Alpha Acid Units (AAUs) or Homebrew Bittering Units (HBUs), are the weight of hops (in ounces) multiplied by the percentage of alpha acids. This unit is convenient for describing hop additions in a recipe because it indicates the total bittering potential from a particular hop variety while allowing for year to year variation in the percentage of alpha acids.[figure 36 – weighing hop pellets]Whenever a brewer is using AAUs in a recipe to describe the quantity of hops, it is important to specify how long each addition is boiled. The boiling time has the largest influence on how bitter a hop addition makes the beer. If no times are specified, then the rule of thumb is that bittering hops are boiled for an hour and finishing hops are boiled for the last 10-15 minutes. Many brewers add hops at 15 or 20 minute intervals and usually in multiples of a half ounce (for ease of measurement).
Calculating Alpha Acid Units (AAU)AAUs are a good way to state hop additions in your recipes. By specifying the amount of alpha acid for each addition, rather than just the weight, you don’t have to worry about year-to-year variation in the hop. An AAU is equal to the % AA multiplied by the weight in ounces.For Example:1.5 oz of Cascade at 5% alpha acid is 7.5 AAUsIf next year the alpha acid percentage in Cascade is 7.5%, you would only need 1 oz rather than 1.5 oz to arrive at the same bitterness contribution.
International Bittering Units (IBUs) The second way estimates how much of the alpha acid is isomerized and actually dissolved into the beer. The equation for International Bittering Units (IBUs) takes the amount of hops in AAUs and applies factors for the boil gravity, volume, and boiling time. IBUs are independent of batch size, and to some extent, independent of the gravity of the beer, unlike the AAU.Hop resins act like oil in water. It takes the boiling action of the wort to isomerize them, which means that the chemical structure of the alpha acid compounds is altered so that the water molecules can attach and these compounds can dissolve into the wort. The percentage of the total alpha acids that are isomerized and survive into the finished beer, i.e. utilized, is termed the “utilization”. Under homebrewing conditions, utilization generally tops out at 30%. Several factors in the wort boil influence the degree to which isomerization occurs. Unfortunately, the way all these factors affect the utilization is complicated and not well understood. However, empirical equations have been developed which give us at least some ability to estimate IBUs for homebrewing.The utilization is influenced by the vigor of the boil, the total gravity of the boil, the time of the boil and several other minor factors. The vigor of the boil can be considered a constant for each individual brewer, but between brewers there probably is some variation. The gravity of the boil is significant because the higher the malt sugar content of a wort, the less room there is for isomerized alpha acids. The strongest bittering factors are the total amount of alpha acids you added to the wort, and the amount of time in the boil for isomerization. Therefore, most equations for IBUs work with these three variables (gravity, amount, and time) against a nominal utilization. The Utilization Equation describes the utilization versus time and gravity of the boil. This allows you to estimate how much each hop addition is contributing to the total bitterness of the beer. By incorporating a factor for gravity adjustment, the IBU equation allows for direct comparisons of total hop bitterness across beer styles. For instance, 10 AAUs in a Pale Ale would taste pretty bitter while 10 AAUs would hardly be noticed in an Imperial Stout. As the maltiness of the beer increases, so does the relative balance between hop bitterness and malt sweetness. A very sweet American Amber Ale needs about 40 IBUs to yield the same balance of flavor as a Bavarian Oktoberfest of the same gravity does with 30 IBUs. The ratio between the bitterness units and the starting gravity is a useful way to compare the bitterness between styles. The BU:GU ratios for several beer styles are plotted in Chapter 20. So, how bitter is bitter? Well, in terms of IBUs, 20 to 40 is considered to be the typical international range. North American light beers, like Coors™, have a bitterness of only 10-15 IBUs. More bitter imported light beers, like Heineken™, have a bitterness closer to 20-25. American microbrews like Samuel Adam Boston Lager™ have a bitterness of about 30 IBUs. Bitter India Pale Ales like Anchor Liberty Ale™ and Sierra Nevada Celebration Ale™ have bitterness of 50 or more. There are several different bitterness equations/models for calculating IBUs currently in use among homebrewers. The Rager, Mosher, Daniels, Garetz, and Tinseth models are the most commonly used. The Tinseth model is presented below. Everyone has their own preference, and your choice is not that critical since the resolution of the human palate is only about 5 IBUs. (This was determined in a blind tasting study using beers that had their IBUs measured using High Performance Liquid Chromatography.) Therefore, everyone is in the same ballpark and that is close enough for comparison.
Calculating Alpha Acid Units (AAU)AAUs are a good way to state hop additions in your recipes. By specifying the amount of alpha acid for each addition, rather than just the weight, you don’t have to worry about year-to-year variation in the hop. An AAU is equal to the % AA multiplied by the weight in ounces.For Example:1.5 oz of Cascade at 5% alpha acid is 7.5 AAUsIf next year the alpha acid percentage in Cascade is 7.5%, you would only need 1 oz rather than 1.5 oz to arrive at the same bitterness contribution.
International Bittering Units (IBUs) The second way estimates how much of the alpha acid is isomerized and actually dissolved into the beer. The equation for International Bittering Units (IBUs) takes the amount of hops in AAUs and applies factors for the boil gravity, volume, and boiling time. IBUs are independent of batch size, and to some extent, independent of the gravity of the beer, unlike the AAU.Hop resins act like oil in water. It takes the boiling action of the wort to isomerize them, which means that the chemical structure of the alpha acid compounds is altered so that the water molecules can attach and these compounds can dissolve into the wort. The percentage of the total alpha acids that are isomerized and survive into the finished beer, i.e. utilized, is termed the “utilization”. Under homebrewing conditions, utilization generally tops out at 30%. Several factors in the wort boil influence the degree to which isomerization occurs. Unfortunately, the way all these factors affect the utilization is complicated and not well understood. However, empirical equations have been developed which give us at least some ability to estimate IBUs for homebrewing.The utilization is influenced by the vigor of the boil, the total gravity of the boil, the time of the boil and several other minor factors. The vigor of the boil can be considered a constant for each individual brewer, but between brewers there probably is some variation. The gravity of the boil is significant because the higher the malt sugar content of a wort, the less room there is for isomerized alpha acids. The strongest bittering factors are the total amount of alpha acids you added to the wort, and the amount of time in the boil for isomerization. Therefore, most equations for IBUs work with these three variables (gravity, amount, and time) against a nominal utilization. The Utilization Equation describes the utilization versus time and gravity of the boil. This allows you to estimate how much each hop addition is contributing to the total bitterness of the beer. By incorporating a factor for gravity adjustment, the IBU equation allows for direct comparisons of total hop bitterness across beer styles. For instance, 10 AAUs in a Pale Ale would taste pretty bitter while 10 AAUs would hardly be noticed in an Imperial Stout. As the maltiness of the beer increases, so does the relative balance between hop bitterness and malt sweetness. A very sweet American Amber Ale needs about 40 IBUs to yield the same balance of flavor as a Bavarian Oktoberfest of the same gravity does with 30 IBUs. The ratio between the bitterness units and the starting gravity is a useful way to compare the bitterness between styles. The BU:GU ratios for several beer styles are plotted in Chapter 20. So, how bitter is bitter? Well, in terms of IBUs, 20 to 40 is considered to be the typical international range. North American light beers, like Coors™, have a bitterness of only 10-15 IBUs. More bitter imported light beers, like Heineken™, have a bitterness closer to 20-25. American microbrews like Samuel Adam Boston Lager™ have a bitterness of about 30 IBUs. Bitter India Pale Ales like Anchor Liberty Ale™ and Sierra Nevada Celebration Ale™ have bitterness of 50 or more. There are several different bitterness equations/models for calculating IBUs currently in use among homebrewers. The Rager, Mosher, Daniels, Garetz, and Tinseth models are the most commonly used. The Tinseth model is presented below. Everyone has their own preference, and your choice is not that critical since the resolution of the human palate is only about 5 IBUs. (This was determined in a blind tasting study using beers that had their IBUs measured using High Performance Liquid Chromatography.) Therefore, everyone is in the same ballpark and that is close enough for comparison.
Hop Bitterness (IBU) Calculations
For those of you who dislike math, I will make this as straightforward as possible. We will use the following “Joe Ale” recipe for our example:
Example Recipe – Joe AleIngredients for a 5 gallon batch 6 lbs. of amber DME 1.5 oz. of 6.4% AA Perle hops(60 minutes) 1 oz. of 4.6% AA Liberty hops(15 minutes)For a 5 gallon recipe, we will boil 1.5 oz of Perle hops for 60 minutes for Bittering, and 1 oz of Liberty for 15 minutes for Finishing. The recipe calls for 6 lbs. of dry malt extract and it will be boiled in 3 gallons of water because of the pot size. The remaining water will be added in the fermentor.
The first step is to calculate the AAUs from the recipe.AAUPerle = 1.5 oz x 6.4% = 9.6AAULiberty = 1 oz x 4.6% = 4.6To calculate how much bitterness the final beer will have from these hop additions, we apply factors for the recipe volume (V), gravity of the boil, and the boil time. The time and gravity of the boil are expressed as the utilization (U). The equation for IBUs is:IBU = AAU x U x 75 / V75 is a constant for the conversion of English units to metric. The proper units for IBUs are milligrams per liter, so to convert from ounces per gallon a conversion factor of 75 (74.89) is needed. For the metric world, using grams and liters, the factor is 10. (For those of you paying attention to the units, the missing factor of 100 was taken up by the % in the AAU calculation.)
Gravity of the BoilThe recipe volume is 5 gallons. The gravity is figured by examining the amount and concentration of malt being used. As noted in the previous chapter, dry malt extract typically yields about 40 pts/lb./gal. Since this recipe calls for 6 lbs. of extract to be used in 5 gallons, the calculated OG is:OG = 6 x 40 / 5 = 48 or 1.048But, since we are only boiling 3 of the 5 gallons due to of the size of the pot, we need to take into account the higher gravity of the boil. The boil gravity becomes:6 x 40 / 3 = 80 or 1.080It is the gravity of the boil (1.080) that is used in figuring the utilization. As you will see in the next section, hop utilization decreases with increasing wort gravity. A higher concentration of sugars makes it more difficult for the isomerized alpha acids to dissolve. I use the initial boil gravity in my utilization calculation; others have suggested that the average boil gravity should be used. (The average being a function of how much volume will be boiled away during the boiling time.) This gets rather complicated with multiple additions, so I just use the initial boil gravity to be conservative. The difference is small—overestimating the total bitterness by 1-3 IBUs.To increase your utilization, and thereby use less hops, you can boil your hops in a lower gravity wort using (for example) half of the total malt extract in the recipe. The other half of the extract can be added at the end of the boil to pasteurize it before cooling the wort, and diluting it to the recipe gravity in the fermentor. UtilizationThe utilization is the most important factor. This number describes the efficiency of the isomerization of the alpha acids as a function of time. This is where a lot of experimentation is being conducted to get a better idea of how much of the hops are actually being isomerized during the boil. The utilization numbers that Tinseth published are shown in Table 7. To find the utilizations for boil gravities in-between the values given, simply interpolate the value based on the numbers for the bounding gravities at the given time. For example, to calculate the utilization for a boil gravity of 1.057 at 30 minutes, look at the utilization values for 1.050 and 1.060. These are .177 and .162, respectively. There is a difference of 15 between the two, and 7/10ths of the difference is about 11, so the adjusted utilization for 1.057 would be .177 - .011 = 0.166The Utilizations for 60 minutes and 15 minutes at a Boil Gravity of 1.080 are 0.176 and 0.087, respectively. Inserting these values into the IBU equations gives:IBU60 = 9.6 x .176 x 75 / 5 = 25 (rounded to nearest whole number)andIBU15 = 4.6 x .087 x 75 / 5 = 6Giving a grand total of 31 IBUs. Utilization numbers are really an approximation. Each brew is unique; the variables for individual conditions, i.e. vigor of the boil, wort chemistry, or for losses during fermentation, are just too hard to get a handle on from the meager amount of published data available. Then why do we bother, you ask? Because if we are all working from the same model and using roughly the same numbers, then we will all be in the same ballpark and can compare our beers without too much error. Plus, when the actual IBUs are measured in the lab, these models are shown to be pretty close. Hop Utilization Equation DetailsFor those of you who are comfortable with the math, the following equations were determined by Tinseth* from curve fitting a lot of test data and were used to generate Table 7. The degree of utilization is composed of a Gravity Factor and a Time Factor. The gravity factor accounts for reduced utilization due to higher wort gravities. The boil time factor accounts for the change in utilization due to boil time:Utilization = ƒ(G) x ƒ(T)where: ƒ(G) = 1.65 x 0.000125^(Gb - 1) ƒ(T) = [1 - e^(-0.04 x T)] / 4.15 FINAL NOTE (2025): There is lots of brewing software out there these days that do these calculations for you.
Gravity of the BoilThe recipe volume is 5 gallons. The gravity is figured by examining the amount and concentration of malt being used. As noted in the previous chapter, dry malt extract typically yields about 40 pts/lb./gal. Since this recipe calls for 6 lbs. of extract to be used in 5 gallons, the calculated OG is:OG = 6 x 40 / 5 = 48 or 1.048But, since we are only boiling 3 of the 5 gallons due to of the size of the pot, we need to take into account the higher gravity of the boil. The boil gravity becomes:6 x 40 / 3 = 80 or 1.080It is the gravity of the boil (1.080) that is used in figuring the utilization. As you will see in the next section, hop utilization decreases with increasing wort gravity. A higher concentration of sugars makes it more difficult for the isomerized alpha acids to dissolve. I use the initial boil gravity in my utilization calculation; others have suggested that the average boil gravity should be used. (The average being a function of how much volume will be boiled away during the boiling time.) This gets rather complicated with multiple additions, so I just use the initial boil gravity to be conservative. The difference is small—overestimating the total bitterness by 1-3 IBUs.To increase your utilization, and thereby use less hops, you can boil your hops in a lower gravity wort using (for example) half of the total malt extract in the recipe. The other half of the extract can be added at the end of the boil to pasteurize it before cooling the wort, and diluting it to the recipe gravity in the fermentor. UtilizationThe utilization is the most important factor. This number describes the efficiency of the isomerization of the alpha acids as a function of time. This is where a lot of experimentation is being conducted to get a better idea of how much of the hops are actually being isomerized during the boil. The utilization numbers that Tinseth published are shown in Table 7. To find the utilizations for boil gravities in-between the values given, simply interpolate the value based on the numbers for the bounding gravities at the given time. For example, to calculate the utilization for a boil gravity of 1.057 at 30 minutes, look at the utilization values for 1.050 and 1.060. These are .177 and .162, respectively. There is a difference of 15 between the two, and 7/10ths of the difference is about 11, so the adjusted utilization for 1.057 would be .177 - .011 = 0.166The Utilizations for 60 minutes and 15 minutes at a Boil Gravity of 1.080 are 0.176 and 0.087, respectively. Inserting these values into the IBU equations gives:IBU60 = 9.6 x .176 x 75 / 5 = 25 (rounded to nearest whole number)andIBU15 = 4.6 x .087 x 75 / 5 = 6Giving a grand total of 31 IBUs. Utilization numbers are really an approximation. Each brew is unique; the variables for individual conditions, i.e. vigor of the boil, wort chemistry, or for losses during fermentation, are just too hard to get a handle on from the meager amount of published data available. Then why do we bother, you ask? Because if we are all working from the same model and using roughly the same numbers, then we will all be in the same ballpark and can compare our beers without too much error. Plus, when the actual IBUs are measured in the lab, these models are shown to be pretty close. Hop Utilization Equation DetailsFor those of you who are comfortable with the math, the following equations were determined by Tinseth* from curve fitting a lot of test data and were used to generate Table 7. The degree of utilization is composed of a Gravity Factor and a Time Factor. The gravity factor accounts for reduced utilization due to higher wort gravities. The boil time factor accounts for the change in utilization due to boil time:Utilization = ƒ(G) x ƒ(T)where: ƒ(G) = 1.65 x 0.000125^(Gb - 1) ƒ(T) = [1 - e^(-0.04 x T)] / 4.15 FINAL NOTE (2025): There is lots of brewing software out there these days that do these calculations for you.