Dip Hopping vs. Coolpooling
There have been so many ways developed to impart different hop notes in beer. Two of the ways I have explored recently are dip hopping and coolpooling. They are similar in that neither method isomerizes hop alpha acids. Without isomerization, the hops do not impart bittering but can add a great deal of flavor and aroma.
In this article I will break down how the two processes work, how they are similar and how they are different, and the impacts I have seen from both. My hope is you will be curious enough about the two techniques to try them in your brewing. The reward for those who do will be unique hop expression and increased aroma in your homebrews.
In 2021, when I first learned about dip hopping from an article in Brew Your Own, I was immediately interested in exploring what it had to offer a homebrewer like myself. A newer process that can increase aromatics and open up flavors in hops not normally tasted? How could I not look into it?
I immediately started a discussion with my brewing partner about the process and in a short time we had our first beers in production using dip hopping techniques. We did a parallel brew of a double IPA and were very impressed with the results. The bittering seemed “softer,” and the hop profiles and aromatics were much more pronounced. We continued our own experiments to make five beers that were dip hopped. This experimentation led to the best double IPAs either of us had ever made. In the last four years I have used this process in over 20 different brews. It’s offered me a way to easily pasteurize the strange herbs and addends I use as a farmhouse brewer while at the same time releasing flavors that I had never encountered before.
The Science Behind Dip Hopping
Dip hopping is a method that helps accentuate pleasant hop aromas while suppressing off-flavors. First developed by brewers at the Kirin Brewery in Japan in 2012, dip hopping involves removing a portion of the wort early in the boil, cooling it, and adding hops to it in a sealed fermenter before fermentation starts. Kirin kept the results of their study very close to the vest for quite some time but revealed some of their results at a brewers’ conference in 2018. The variables they experimented with were temperature, volume of liquid, amounts and types of hop products added, and time of contact.
This technique is believed to produce a few notable effects. The main one is the volatilization of myrcene (β-myrcene), a hop monoterpene that can contribute harsh flavors to beer. Myrcene is a naturally occurring compound found in various plants like hops and cannabis and is known for its grassy, earthy, and sometimes musky aroma. It is one of the key components of hop aroma so it might seem counterintuitive to reduce this hydrocarbon. But by suppressing this component in the liquid and holding it in the wort as a gas, other much more pleasant aroma components are brought to the forefront. Some brewers have reported amplified linalool and geraniol through reduction of myrcene in their own experiments.
One of the most exciting discoveries for me has been the unlocking of new flavors from familiar varieties of hops. Azacca® and Enigma® are two hop varieties that typically offer spicy notes. The flavor notes in my own trials were significantly changed in these two varieties of hops through the dip-hop process. Other hops that will benefit from this process are the hop varieties already rich in geraniol or linalool.
Popular geraniol-rich hop varieties:
Cascade
Mosaic®
Citra®
Bravo
Amarillo®
Comet
Pacific Hallertau
Southern Cross
Centennial
Chinook
Motueka™
Styrian Golding (Celeia)
Popular linalool-rich hop varieties:
Amarillo®
Cascade
Columbus
Centennial
Mt. Hood
Nugget
Pacifica™
Willamette
Cluster
The dip-hop process can also suppress the production of 2-Mercapto-3-methyl-1-butanol (2M3MB), an off-flavor that can make beer taste onion-like. The suppression of this compound is partly due to lower hydrogen sulfide content in the beer, which is typically associated with the development of off-flavors. There are other things brewers do to reduce the formation of this chemical like controlling oxygen levels during wort preparation, but dip hopping really seems to do the job.
My Experience with Dip Hopping
I have always used boiled wort for my dip-hop additions and have experimented extensively with a contact time of 20–30 minutes with good results. The variables I’ve played with are choice of hops, quantity and types of additions, volume of liquid for steeping, and time in contact. Brewing 5-gallon (19-L) batches, I typically dip hop using 1–2 gallons (4–8 L) of wort (enough to cover the addition with liquid). Keep in mind, pellet hops will absorb liquid and solidify, so be sure to add enough wort to overcome this absorption. I finish the boil and transfer wort at 180 °F (82 °C). At this temperature I am effectively pasteurizing anything that is added to the beer while staying below the temperature where isomerization of the hops occurs. With my system, the dip-hop addition will free fall in temperature to about 150 °F (66 °C) while the remaining wort is cooling. Myrcene volatilizes at 150 °F (66 °C) so this temperature drop works throughout the steeping time. In my studies I have put an airlock on the fermenter to see how long the off-gassing continues, but I now seal the fermenter to hold as much in the way of aromatic compounds as possible in the wort.
I bag what is added to the fermenter, and pull it out prior to transferring the larger volume of cooled wort. I have been successful top cropping yeast if the dip-hop addition is small, (2 oz./56 g or less). But be prepared to lose the ability to harvest yeast if you decide to dip hop. I calculate the IBUs by considering the dip hop as a whirlpool addition. The dip-hop bitterness is softer — very much like a mash-hop addition. This is ideal for hazy IPAs and some less bitter styles, though at times, this soft bitterness has proven to be a bit too soft for my palate and I have adjusted some of my West Coast IPA recipes for a sharper hop note.
Coolpooling
When I started seeing the positive results of dip hopping firsthand, I could not for the life of me understand why more commercial brewers were not doing it. Shortly after starting my journey with dip hopping, Lagunitas made a beer called, “Dip Trip, Free Ride IPA.” In promotional material accompanying the beer at the time, it stated: “The wizard brewers of Lagunitas invented a brand-spankin’-new style of IPA just for IPA Day.” The “brand new” part, which is up for debate, was free rise (no temperature control and dip hopping). After this beer, I heard very little about commercial brewers using the process, but I did hear and see mentions of “coolpooling” from quite a few pro breweries.
Coolpooling is adding hops to cooled wort. Sometimes this addition is in the brew kettle, and other times it is in a secondary vessel. Many commercial brewers do it at 170–180 °F (77–82 °C), but some are known to do it at much cooler temperatures. Some brewers do it in place of whirlpooling in recipes (which consists of adding hops at flameout), and others do both; but either way the goal seems to be the same: Add full hop flavor and aroma without adding bittering.
“We do tend to get better fruit character from the hops with what I’d call a more refined aroma and flavor (through coolpooling),” explains Vinnie Cilurzo, of Russian River Brewing Co. “Bitterness is also lower due to less isomerization, so that needs to be taken into account.”
To learn more about the process of coolpooling, I asked some of the brewers doing it to share how they coolpool with me:
“We get down to about 180–185 °F (82–85 °C) using approximately 10% filtered room temperature water. One of the biggest keys to coolpooling is what temperature water you use. Some brewers will use cold liquor water, which allows you to get a cooler wort by using less diluting water to get to 180–185 °F (82–85 °C). We are careful to not go below 180 °F (82 °C) as this is the temperature known to keep things sterile.”
– Vinnie Cilurzo, Russian River Brewing
“We don’t add any hops until the coolpool. When we finish our boil (we shorten this to 60 minutes vs. 90 for most of our beers), we run the wort through our counterflow heat exchanger until it reaches 170 °F (77 °C). Then we add a heavy hop addition. We double the contact time we normally use (30 minutes vs. 15 minutes).
– J. Shilling, Dirt Road Brewing
“I use that technique on a select few of my beers. I pre-chill the entire batch and generally take it to 180–190 °F (82–88 °C) depending on what I am trying to achieve. We begin our 30-minute wort chill about 20 minutes after the whirlpool is complete.”
– John Kimmich, The Alchemist
“I personally haven’t found a big difference in the hop aromatics; we just use whirlpool temperature as a tool for controlling bitterness. Originally, we whirlpool in the kettle, so we’d recirculate through the heat exchanger and back into the kettle to get to the target temperature. Then we’d bypass the heat exchanger and pump for 20 minutes with the hops in there. Then settle for 20 minutes, then run off for ~30 minutes depending on how quickly we could knock-out. We now have a dedicated whirlpool, so we go through a shell and tube heat exchanger onto the hops. Now it’s just the momentum of the transfer that keeps it spinning. Closer to 10 minutes going in, 20-minute rest, 30-minute knockout.”
– Michael Tonsmeire, Sapwood Cellars
Whirlpooling vs. Coolpooling
Whirlpooling hot wort after boiling is used to remove hop material added during the boil. Because the wort is hot enough to isomerize alpha acids, heavy late additions of hops add significant bitterness. When coolpooling, the wort temperature is reduced before the last hot-side hop addition so hop aroma is extracted but alpha acids are not isomerized. Some brewers cool their wort by adding cold water to the kettle and others slightly cool their wort with a wort chiller. With a quicker wort cooling process in coolpooling, brewers are able to preserve terpene compounds and more of the delicate hop flavors and aromas in this hop addition. Rapid cooling also helps prevent the formation of dimethyl sulfide (DMS), a compound that can impart a “cooked vegetable” flavor to beer. In addition to these benefits, the process also aids in settling solids (trub) in the kettle, leading to a clearer beer to transfer out of the fermenter.
With recent products such as Abstrax® terpene extracts hitting the market, we have more ways to add terpenes to beer later in the process, but if a brewer could avoid the additional expense of these additives, why not? These products still seem like a good thing to have in the brewer’s toolbox to really “dial in” the desired hop flavor profile, but getting a head start helps and many brewers use both to really pack an aromatic punch.
How is Dip Hopping Different Than Coolpooling?
I have found between these two processes that dip hopping suppresses off-flavors while opening up the possibility of accessing new flavors, while coolpooling maintains and enhances more subtle flavors already present in the wort. The big difference in these techniques is that hop solids are removed from wort when coolpooling — as the wort is transferred after a period of coolpooling, leaving the majority behind. Because hop solids remain in the wort/beer when dip hopping, more nucleation sites are added to the fermenting beer. This is why Kirin believes that dip hopping suppresses less desirable “grassy” characteristics of myrcene. Another difference is dip hopping requires sealing the fermenter, ideally preserving more of the aroma compounds.
For commercial brewers, dip hopping can be problematic — which is likely why is isn’t utilized more on the larger scale. Either their systems are not set up to transfer wort to a separate vessel or they lose the ability to harvest yeast due to it, which can be a significant cost factor. Coolpooling seems to be much more easily done on a commercial system. Both methods amplify hop taste and aroma while minimizing bitterness additions, but the science and processes to achieve these results seem very different. Coolpooling is a gentler method for drawing out hop character while preserving subtler flavors that could be overwhelmed by more aggressive methods.
For brewers looking for a harmonious beer, blending the two could help create something more complex with many layers of hop expression, including more subtle flavors that you may have never tasted before. Dip hopping could give that fresh hop hit, while coolpooling could round out the flavors and help integrate them into a more cohesive whole. This approach would definitely require careful consideration of timing and amounts to ensure that the combination isn’t overwhelming, but it’s certainly an interesting avenue to explore.
I see these two processes this way: Dip hopping offers access to new flavors/aromas. Coolpooling gives the brewer a tool to access more subtle flavors/aromas while rounding them out.
My Experience with Coolpooling
In the last few years, I have become focused on the idea of balance in my beers. With IPAs and double IPAs I work with the bitterness units-to-gravity units (BU/GU) ratio as a starting point when designing recipes. A commercial brewer told me he looks at balance using a simple formula of 8–10 IBUs per percentage of alcohol in his finished IPAs. This formula is a quick and easy way to look at the hop balance in my beers, but there is a mathematic formula available to calculate it more precisely. This works with the addition of a “perceived bittering” calculation in addition to the somewhat simpler BU/GU formula. This perceived ratio takes into account the finishing gravity of the beer; sweeter beers do not manifest as bitter on the palate as drier beers do. Neither of these calculators take into account that bittering could be added to the beer with ingredients other than hops, nor do they account for bitterness from hop compounds other than iso-alpha acids.
Since I started looking at this balance ratio, the IBUs in my beers have consistently come down. Some of it is due to a change in my palate, but much of it has to do with the different late-addition processes I now use adding hops to beers. For my test beer I decided to shoot for the low end of the IBU range and see if coolpooling really enhanced the hop expression of flavors and aromatics.
I would commonly design a double IPA recipe like the one to the right with 80 IBUs. However, the Coolpooled IPA calculates to 58, (this results in a BU/GU of 0.725). The IBU range for DIPAs according to the Beer Judge Certification Program (BJCP) is 60–120, so looking at their scale I am at the low end of the range. The final gravity of this beer also did not finish as low as expected, with fermentation stopping at 1.018, which means that it is sweeter than I normally get. I usually hit 1.012–1.014 FG on these styles. If I would have hit these finishing numbers, I would have had an even greater hop punch. I’ll add my reflections on the results following the recipe.
Coolpooled DIPA Recipe
(5 gallons/19 L, all-grain)
OG = 1.081 FG = 1.018
IBU = 58 SRM = 7 ABV = 8.3%
Ingredients
13 lbs. (5.9 kg) pale 2-row malt
3 lbs. (1.4 kg) white wheat malt
8 oz. (230 g) dextrin malt
13 AAU Centennial hops (15 min.) (1.25 oz./35 g at 10% alpha acids)
20 AAU CTZ hops (15 min.) (1.25 oz./35 g at 16% alpha acids)
0.75 oz. (21 g) Centennial hops (coolpool)
0.75 oz. (21 g) Chinook Cryo Hops® (coolpool)
2 oz. (56 g) Mosaic® hops (dry hop)
Yeast nutrient (15 min.)
Whirlfloc (15 min.)
Omega Yeast OYL-071 (Lutra Kveik) or your favorite neutral yeast such as Wyeast 1056 (American Ale) or SafAle US-05
3/4 cup corn sugar (if priming)
Step by step
This recipe uses a “Light Hoppy” water profile. Mash in all of the grains at 150 °F (66 °C) with 6 gallons (23 L) of water. After 45 minutes, batch sparge with 5.5 gallons (21 L) of water at 170 °F (77 °C). With my system I ended up with 7.5 gallons (28 L) in the boil. My evaporation rate is 10% per hour. You should adjust the sparge amount based on your evaporation rate — shoot for 7.5–8 gallons (28–30 L) in the boil for a 5-gallon (19-L) batch.
This is a 90-minute boil. Begin boil and after 75 minutes add the 15-minute hop additions. At the end of boil, rest for 15 minutes. Add 10% cold water (about 3 quarts/L), then cool to 180 °F (82 °C) with your chiller. I used the coolpool process described by Vinnie Cilurzo at Russian River Brewing. When the target coolpool temperature of 180 °F (82 °C) is reached, add the coolpool hop additions and hold this temperature for 20 minutes.
After the coolpool, continue chilling the wort to yeast-pitching temperature (I fermented with kveik at 80 °F/27 °C, but other yeast will be cooler). When fermentation is complete, package as usual.
Extract version: Substitute the pale and wheat malts with 7 lbs. (3.2 kg) light dried malt extract and 1.5 lbs. (0.7 kg) wheat dried malt extract. Bag the dextrin malt and add it to 6 gallons (23 L) of water as you slowly bring it up to 170 °F (77 °C) and rest there 10 minutes. Remove grains and bring to a boil. Turn off heat and stir in malt extracts, being careful not to scorch any on the bottom of the kettle. Once dissolved, return to heat and follow the remainder of the all-grain recipe.
Reflections:
The bittering notes were more subdued than I would like due to the low attenuation, but the flavors and aromatics were definitely enhanced from coolpooling. There is also a fruitier tone to the hop build, which I am pretty sure did not come from increased ester production of the yeast. (Lutra is very neutral at lower fermentation temperatures.) After having the beer in the keg for a month, I found that the aromatics maintained their punch and the increased hop expression held up. The only tools I have used in my brewing that offered a similar long-term benefit were thiol-enhancing yeasts and processes.
Since I can cool 5-7 gallons (19–26.5 L) of beer with a 50-foot (15-m) stainless immersion chiller rather quickly, I am not really sure this technique is as effective for my small system as it might be with a larger volume, but if it offers subtle flavors that would not normally be perceived it is a winning technique that is worth exploring.
