Hop Extracts – Advanced Brewing

Molecular gastronomy (MG) is an exciting and occasionally contentious aspect of modern fine dining. MG is an approach to cooking that re-appropriates compounds and equipment developed for large-scale commercial food production to achieve flavors or textures impossible with traditional recipes. A few brewing ingredients even have assumed prominent roles in MG; these include maltodextrin (oil powders), carrageenan extracted from Irish moss (dairy gels), and calcium chloride (spherification). In most cases the final dish also includes foraged, local, or artfully cooked ingredients that are highlighted by the unique presentation. Craft breweries are slowly embracing concepts similar to the culinary world, brewing delicious beers enhanced by ingredients created for macro breweries.

There will always be brewers who prefer to use only the most natural ingredients out of tradition. Any German will tell you that you need nothing more than malted grain, isolated yeast, untreated water, and hops to make a nearly perfect beer. However, highly-processed ingredients are becoming more common: Although wort isomerizes alpha acids and two of the most effective natural solvents (water and ethanol) extract hop aromatics from whole hop cones, many brewers, for convenience and economics, prefer additional pre-processing, using pelletized hops or even concentrated “Type 45” and “Cryo” hops. That may be good enough for some, but further industrial chemistry can save money, time, effort and, perhaps with the right touch, produce a superior beer. A huge range of hop extracts originally developed for large breweries are gaining acceptance with both craft brewers and homebrewers.

The leaf-like parts of the hops suck up wort thus lowering efficiency, clogging valves, and causing issues for harvesting yeast. Even pellet hops can be bulky to ship and store, sensitive to oxygen, and sometimes inconsistent. Hops contain hundreds of components including alpha and beta acids, hydrocarbons, thiols, tannins, enzymes, terpenes, and glycosides. The exact compounds and amounts differ depending on variety and growing conditions. Even with ideal storage (cold and low-oxygen), the ratios shift over time. Some processors isolate and concentrate specific hop compounds so that each can be added to either enhance or minimize a desired attribute. These hop extracts roughly fall into two categories, those primarily intended to add bitterness and those where aromatics are the goal.

Hop Bitterness

CO₂ Hop Extracts

CO₂ hop extract is a sticky honey-like resin collected from the lupulin glands by supercritical CO₂ (high-pressure liquid).¹ This is a relatively eco and health-conscious approach compared to industrial solvents used in the past. CO₂ hop extracts contain alpha and beta acids as well as many aromatic oils. They do not include glycosides, which are water soluble and located in the green parts of the hop (see “The Science of Hop Glycosides”, BYO July/August 2015). While there are varietal-specific CO₂ extracts, most such products available to homebrewers are generic.

CO₂ hop extracts contain alpha acids that, just like those in hop cones or pellets, require isomerization to provide substantial bitterness. Typically, alpha acids are 30-50%, and the form also encourages higher-than-typical utilization (~35%).

Usually these extracts are added early in the kettle instead of or in addition to a bittering hop. I find the sensory bitterness contribution to be lower or perhaps “smoother” than an equivalent estimated IBU from actual hops. This perception is a result of the extract not contributing polyphenols, including tannins, which increase perceived bitterness. Extracts also allow for better yields, eliminating hop wort-absorption; this is especially beneficial in styles with large bittering charges such as a West-Coast DIPA or American barleywine.

Craft breweries buy CO₂ hop extracts canned and usually design recipes to use an entire can in each batch (for example enough to add 30 IBUs to 30 bbls) to avoid measuring smaller quantities. For homebrewers, these cans aren’t practical because even the “small” ones are enough to add 50 IBUs to 297 gallons (1,124 L) of wort; instead CO₂ extract is repackaged in small syringes (e.g., HopShot). 1 mL adds approximately 10 IBUs to 5 gallons (19 L) of wort. Store the extract in the freezer, and either take it out the night before brewing or place the syringe in a glass of warm water to make the extract easier to dispense directly into the boiling wort. While the cans are shelf-stable for extended time at room temperature, I have had issues with unopened syringes darkening and even going off in the freezer when stored for an extended time.

Pre-Isomerized Hop Extracts

Another class of bittering products is pre-isomerized hop extracts. These are intended to be dosed into the beer post-fermentation as an easy way to increase bitterness in beer that does not taste as balanced as intended. These extracts do not contribute any hop aroma. The extraction process starts with pure alpha acids refined from hops, often initially like CO₂ extract. Subsequent processing determines the configuration of the iso alpha acid. In the case of rho-isohumulones, heat and sodium borohydride isomerize and reduce the alpha acids by hydrogenating them. For tetra hydro-iso-alpha a slightly different configuration is created by hydrogenating the alpha acids in the presence of a palladium/carbon catalyst. Hexa hydro-iso-alpha acid combines the processes that create tetra and rho.²

There are other benefits to these products in addition to convenience. As a result of the treatment these iso-alpha acids do not skunk like alpha acids isomerized in the boil because the side-chain of the molecule has been reduced preventing the reaction that leads to skunky 3-methyl-2-butene-1-thiol (MBT).³ Miller is able to bottle their beer in clear glass because they use tetra hydro-iso-alpha acid as the sole hop addition. Reduced alpha acids could be used to beautiful effect in a colorful low-hopped fruit beer in clear bottles without fear of skunking!

Even if you are planning to keg your beer or store it in brown bottles you might consider these pre-isomerized extracts for their positive impact on head retention. Kalsec found that each 1 ppm (1 IBU) of Tetralone (their version of tetra) increased head retention by 10-12 seconds.⁴ I chose to add 1 g of Tetralone as the only hop addition to a 5-gallon (19-L) batch of quick-soured beer with stone fruit and vanilla (see recipe at the bottom of this article). This approach allowed the Lactobacillus to work without inhibition, and provided a relatively substantial head especially when served on beer gas through a stout faucet! See “Nitrogen and Stout Faucets”, BYO November 2015.

These extracts also influence body, with hexa adding a rounder mouthfeel. I haven’t split a batch to gauge the difference for myself, but I did not find hexa to be especially foam or body-positive in a New England-style IPA which already had plenty of other hop compounds. Hexalone is available as Kalsec Head Master, which they promise will soon be available in smaller quantities more reasonable for homebrewers.⁵ Precise measurement is important with such concentrated products; a scale with 0.1 g precision and a few disposable pipettes can make the task easier.

Hop Aroma

There are also hop extracts that add aroma. Rather than select hop varieties high in a particular molecule, you can purchase concentrated aromatics. Unfortunately there aren’t many available in homebrew-scale packaging at this time, but they have slowly been gaining popularity with craftbrewers to augment traditional hopping.

A varietal CO₂ extract can be added late in the boil or to the whirlpool alone or in combination with hops. The advantages are similar to bittering in terms of losses, storage, and consistency. However, one study from Weihenstephan suggested that the delicate aromatics volatilize more easily than traditional hop forms.⁶

Other products have removed the bittering components and concentrated the aromatics alone. Usually this type is best saved as a final boost of aroma right as the beer is being packaged. A few extracts blended to impart a particular profile include: Kalsec Hopfenatic (for IPAs) and Hop HySterian (for Pilsners).

Concentrated varietal hop essential oils can be added, boosting hop aroma. For craftbrewers these are available from Hopsteiner and Barth-Haas. As they are oil, and beer is mostly water the two don’t mix well especially at higher rates. To encourage emulsion, the hop oil is diluted in propylene glycol to act as a dispersant.⁷ BREWFERM Hop Sensation is sold to homebrewers in versions including Citrulicious and Kentish Gold.⁸ These are pre-diluted in monopropylene glycol and can be added directly to beer post fermentation.

You could even try making your own hop aroma extract! The simplest option is to steep hops in vodka to create a tincture to be dosed into the finished beer to taste. A more labor-intensive option is to use an essential oil distillation rig, such as the PicoStill, to pass steam through the pulverized hops, carrying the aromatics along for the ride. The oil and water naturally stratify allowing for separation. This approach is similar to that used by Sierra Nevada for their Hop Hunter IPA.

One potential benefit of hop aroma oils as compared to dry hopping is the elimination of “hop creep.” Hops contain enzymes that when added after cooling are capable of converting unfermentable dextrins into fermentable sugars, causing renewed fermentation. While a recent area of interest, the phenomenon was written about as long ago as 1939 in “The Diastatic Activity of Hops, Together with Note on Maltase in Hops”.⁹ In addition to over-attenuation, “hop creep” can cause other issues as the stressed fermentation leaves diacetyl. Certain hop varieties (anecdotally, Mosaic®), contain more of these enzymes than others. By adding processed hop products for a post-fermentation addition, you remove this risk. The other solution, mentioned to me by brewers at Modern Times Beer Co. and North Park Beer Co., is to soft-crash to 58 °F (14 °C) before dry hopping to prevent a renewed fermentation.

Extracting Excitement

For me, what matters most is the result in the glass (and the hop aroma floating out of it). If you add hop extracts to cut costs or make brewing easier, that is fine, but my excitement comes in using them as part of my search to brew the most delicious beers possible! In some cases, hop extract has allowed me to brew beers not possible with more traditional whole or pellet hops.

Some of these products are difficult or expensive to procure in homebrew quantities; but with increased demand, it’s likely more companies will come along willing to create packaging more suited to a smaller scale.

Sources

¹ https://ychhops.com/hop-products/resinate-co2-hop-extract
² https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/alpha-acid
³ https://beersensoryscience.wordpress.com/2011/03/17/lightstruck/
⁴ Kalsec Advanced Hop Bitter Extracts
⁵ https://www.brewersfriend.com/forum/attachments/kalsec-hop-bitter-extracts-explained-pdf.1778/
⁶ Oxford Companion to Beer: Hop Extracts p. 456
⁷ https://www.hopsteiner.com/wp-content/uploads/2017/11/14_08_HopOil.pdf
⁸ https://www.brouwland.com/content/docs/Brewferm_Sensations_Guide_EN_LR.pdf
⁹ https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1941.tb06070.x

Recipe

Nitro Stonefruit Sour

(5 gallons/19 L, all-grain)
OG = 1.044 FG = 1.011
SRM = 3 IBU = 6 ABV = 4.3%

The vanilla helps to make a more sherbet-like balance. You can add lactose to taste at packaging if you want more sweetness. The hop extract increases head retention, improving the perceived creaminess of the body and appearance of the beer. Lowering the pH before souring reduces protein breakdown by the bacteria, improving body and head retention.

Ingredients
9 lbs. (4.1 kg) Dingemans Pilsen malt
2 lbs. (0.91 kg) flaked oats
1 vanilla bean (day 5)
6 lbs. (2.7 kg) white nectarines, sliced or pureed (day 7)
4 lbs. (1.8 kg) white peaches, sliced or pureed (day 7)
1 Tbsp. lactic acid
1 g Kalsec Tetralone (tetra iso extract) (keg or bottling bucket)
2 GoodBelly Straight Shot (Lactobacillus plantarum)
Safale S-04 or Wyeast 1099 (Whitbread Ale) yeast
4 oz. (113 g) table sugar (if priming)

Step by Step
My water profile was as follows, 85 ppm calcium, 75 ppm chloride, 90 ppm sulfate, 15 ppm sodium, 10 ppm magnesium, and 90 ppm bicarbonate. Mash at 152 °F (67 °C) for 45 min. The wort is not boiled, only heated to 170 °F (77 °C), then chill to 85 °F (29 °C). Pitch two Goodbelly Straight Shots or another source of Lactobacillus brevis or Lactobacillus plantarum of your choice. Lower wort pH to 4.4-4.5 with approximately 1 Tbsp. (15 mL) of lactic acid. Leave at 68-70 °F (20-21 °C) to sour. After 24–36 hours of souring, aerate and pitch rehydrated S-04 or an English ale yeast strain of your choice. You may want to pasteurize the wort prior to pitching the brewer’s yeast if you want to mitigate the risk of Lacto infection in your brewery.

After five days, add one vanilla bean, split lengthwise. After a week, add fruit. Slice or puree the fruit discarding the pits but retaining the skins. After two weeks on the fruit, package adding the hop extract to the keg or bottling bucket while siphoning the beer. If serving on nitrogen, chill and pressurize to 20-25 PSI with beer gas. Otherwise, package the beer as you normally would.

Written by Michael Tonsmeire