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Hop It Like It's Hot: Whirlpools, “Dip Hopping,” and More Ways to Squeeze Out Aroma

Pull levers, turn knobs, spin wort—from whirlpools to “dip hopping,” here is a detailed look at some specific hot-side techniques and gear for dialing in substantial hop flavor and aroma.

John M. Verive Dec 11, 2020 - 14 min read

Hop It Like It's Hot: Whirlpools, “Dip Hopping,” and More Ways to Squeeze Out Aroma Primary Image

Photo: Courtesy Breakside Brewery

Regardless OF whether you like your IPAs dry, bitter, and pilsner-clear, or dense, soft, and opaque with polyphenol haze, you’re sipping them because of how they leverage the wondrous hop flower. No other beverage so effectively captures the myriad aromas and flavors contained within those pungent catkins. Short of packing a vaporizer with a bowl of freshly rubbed hops, IPA is your best bet for experiencing the “surreal expression of what hops are.”

Bob Kunz, founder and brewmaster of Highland Park Brewery in Los Angeles, dropped that “surreal expression” line on me while discussing his approach to IPA brewing. His team’s target varies with each new IPA they brew—their output ranges from classic West Coast–style to new-school soft and hazy ales to the more recent attempts to find a middle ground—but Kunz says his ultimate goal is to “maneuver all the knobs available in the brewery to fully realize my vision.”

When brewing IPA, Kunz envisions a beer that not only provides the “pure experience of hops,” akin to sticking your head in a fresh sack of hops, but also a beer that contains a “through-line” of hop expression, from the initial pour to the sensations that linger even beyond the beer’s finish. He wants his beers to tell the hops’ story with a beginning, a middle, and an end. To establish the plot, he adds hops throughout the brewing process with time-tested techniques—including doses of aroma hops added to the whirlpool after the boil.

Whirlpool Design

In designing the brewhouse at Highland Park’s second location, Kunz got help from Tim Heath. The former engineering director at Premier Stainless, Heath now helps breweries design new systems and processes. Heath breaks down the design of late-hop-friendly whirlpool vessels into three aspects: getting wort in, the geometry of the vessel itself, and getting wort out. The goals are high velocity, good hop contact, the development of a dense cone of solids, and efficiency in separating the wort from those solids.

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“It’s hard to move a static body of liquid, and you want to get the mass moving as quickly as possible,” Heath says. The swirling inside the vessel is created by a high-velocity stream of liquid at the inlet of the whirlpool. Ideally, the flow from the kettle doesn’t lose any velocity at the whirlpool inlet, and the exact position, direction, and size of this port is crucial to whirlpool performance. “The hardest work a pump sees in the brewhouse is pulling dense, 212°F [100°C] liquid out of the kettle,” he says, to illustrate the importance of rugged, high-velocity pumps. Once the wort is transferred and swirling inside the tank, centripetal force pulls any solids into the center of the whirlpool and deposits them as a cone. Ports ideally positioned along the sides of the tank, just above that cone, draw off the clarified wort. Some whirlpools have a barrier between the cone and the draw-off ports to help prevent solids from leaving with the wort.

Layering Hops for Better IPA

In the world of cutting-edge IPAs, little tweaks to processes can make big changes in the finished beer. Heath says he’s seen brewers scale back their focus on whirlpool-hop additions in recent years. The brewers I spoke to agreed, often putting more emphasis on dry hopping. Sam Richardson from New York’s Other Half Brewing says his late-hopping regimens for IPA are fairly minimal, rarely more than a pound per barrel. “I think you see more whirlpool additions on the West Coast,” he says. Hops bring bitterness to beer no matter when they’re added, but the intensity and character of that bitterness changes depending on many factors. Each hop dose adds more variables to the brewing equation, and big charges of hops in the whirlpool can quickly push the bitterness out of balance—especially for hazy IPA brewers looking to minimize bitterness while maximizing hop impact.

“You can see some negative flavors from big whirlpool additions,” says Tim Sciascia, co-owner and head brewer at Cellarmaker Brewing in San Francisco. Cellarmaker is a lauded California IPA brewery whose products have evolved as the style diverged from the West Coast paradigm. Big whirlpool additions were common in the seven-year-old brewery’s early IPAs, but the increased focus on dry hopping can overshadow the impact of whirlpool hops. “Whirlpool additions are a big part of the complete hoppy experience but not as big a factor as we thought they would be,” Sciascia says.

So why bother with whirlpool additions at all? It goes back to Kunz’s “through-line” and “brewery knobs.” Adding hops post-boil, but still on the hot side, maximizes the amount of volatile aroma compounds extracted, but it minimizes the bittering that occurs at higher temperatures. It provides a sensory link between the structure of the hops added to the boil and the aromatic impact of dry hopping. “If you layer hops in the process, you get a more layered character in the finished product,” Kunz says. Late hopping is an opportunity to bring another layer to an IPA. Controlling the wort temperature and contact time during these hop additions are two more levers that a skilled brewer can pull to change the final flavor and aroma of their brews.

For Van Havig at Oregon’s Gigantic Brewing, late-hop additions are crucial even though he doesn’t have a dedicated whirlpool vessel in the brewhouse. The brewery uses all whole-cone hops, making whirlpool hopping logistically impractical. Instead, the brewery whirlpools in their 15-barrel kettle and then pumps the hot wort into a 21-barrel hopback vessel, which is stuffed with 10 to 40 pounds of whole-cone hops. Not only does this hop addition provide a boost of flavor and aroma, but the hop matter acts as a filter bed to catch the trub, hot break, and hop particles from the kettle.

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Dip Hop and Chill.

The process at Gigantic starts with wort just off the boil and lasts for about 70 or 80 minutes of total contact time with the hops. They have dialed in the process to make the most of the whole-cone hops, and Havig has another trick up his sleeve for when they want to focus on the more delicate volatiles in the hops—flavors and aromas that don’t survive the hotter wort temperatures and longer time in the hopback—or when they want to minimize additional bitterness via isomerization: It’s called dip hopping.

Havig describes dip hopping as a technique borrowed from Spring Valley Brewery in Japan—part of Kirin’s craft division. It combines lower-temperature late-hop additions, this time in the fermentation vessel, with exposure to active fermentation (and that brewer’s buzzword: biotransformation).

The Gigantic process is straightforward: load the late-hop addition into the empty fermentation vessel, purge the tank with CO2, then add some hot liquor at your target extraction temperature to create a concentrated hop tea in the tank. Hopping rates are similar to whirlpool additions—0.75 to 1 lb (340 to 454 g) per barrel—and a half barrel of hot liquor is used for each 11 lb (5 kg) of hops. Target temperatures are 150–170°F (66–77°C), and the hops steep for about an hour before the brewers pump cooled wort into the tank and pitch the yeast. Havig says that between the lower-temperature hop extraction and the effect of active yeast on the hop matter, the aromas and flavors produced are vibrant and complex.

The processes at Gigantic touch on the biggest challenges for whirlpool-hop additions. First, of course, there’s the need to have a whirlpool vessel. Gigantic gets around it with both a hopback and their novel dip-hopping method. Once the main hardware is sorted, brewers have to deal with the disparity between wort at almost 210°F (99°C) and the ideal extraction temperatures for whirlpool additions (150–195°F/66–91°C). There are two common methods for getting the wort into the target temperature zone: transferring through a heat exchanger or watering back the wort with cold liquor to hit the target temperature. The latter method will of course reduce the gravity of the wort, so a stronger wort must be made with this dilution in mind. Depending on the temperature of the cold liquor, a substantial volume of water may be needed to drop the temperature enough, and the mineral content of the cold liquor can impact the flavor of the cooled wort. It is a resource-inefficient method that adds more variables and complexity, but it doesn’t require much extra equipment (though the mash tun must be sized to handle the higher-gravity wort production).

The heat-exchanger solution is similar at first blush, but unfiltered wort from the kettle is full of hot break, trub, and hop particles that will quickly clog a common plate-and-frame heat exchanger. A separate in-line filter is required before the heat exchanger to catch the solids before they block the flow of wort and cause significant maintenance issues.

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In Portland, Oregon, Breakside Brewery has a custom shell-and-tube-style heat exchanger from JV Northwest. Not prone to clogging the way plate-and-frame units are, the shell-and-tube units have higher throughputs, an important consideration for Brewmaster Ben Edmunds. He says that the unit will drop the temperature of 10 barrels of hot wort by 30°F (17°C) in about 10 minutes. “We could go lower,” Edmunds says. “Some breweries have great success with whirlpooling at around 160°F [71°C], but any lower than 180°F [82°C], and our quality assurance team gets nervous.”

While more pivotal variables in recipe and process might overshadow them, whirlpool additions and other late hot-side hopping techniques provide fastidious brewers with more knobs to turn in their search for the most expressive beers. And while we may not all agree on the specifics of the perfect IPA, we can all get behind brewers developing their skills to extract the most out of every hop flower that goes into their beers.

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The four-vessel brewhouse at Breakside Brewery's Slabtown Pub was specifically designed for flexibility in brewing hop-forward beers.

Whirlpooling in the Home Brewery

Adding post-boil hot-side hops to a batch of homebrew is comparatively simple. The smaller batch sizes and hop doses minimize many of the challenges of whirlpool additions at the commercial scale. Of course, you probably don’t have a dedicated whirlpool vessel in your garage brewery, but here are three options for boosting the aroma of your custom IPAs.

Whirlpool in the Kettle

If you use an immersion counterflow chiller in your brew kettle, you can add a hop dose while your wort is cooling. It’s a time-tested method for homebrewers to add big charges of flavor- and aroma- boosting hops, but Sam Richardson from Other Half suggests using a mesh bag or some other way to contain the hop particles, lest you have a messy slurry to deal with alongside decreased wort yields.

Use a Hopback

You could repurpose a carboy or other vessel as a hopback between the kettle and your fermentation vessel (or make your own hopback—see “DIY: Make Your Own Hopback,” beerandbrewing.com). You’ll also need a pump to move the hot wort and a way to chill the liquid in the kettle to your target temperature (try about 180°F/82°C to start). Just add your dose of late hops to the hopback and rack the wort onto the hops. Give it between 45 and 60 minutes of contact time, then rerack the wort into your fermentor. Be mindful of wort temperature when you pitch your yeast though—it might be necessary to rack to an intermediate vessel with an immersion chiller to further cool the wort.

Try the Dip Hop

Oregon’s Gigantic Brewing uses a technique called “dip hopping” when they want to focus on the more delicate volatiles in the hops or when they want to minimize additional bitterness via isomerization. The hardest part about adapting the process to the homebrew scale is the math, but for a 5-gallon (19-liter) batch, it works out to about 2 oz (57 g) of hops steeped in 20 fl oz (591 ml) of hot water.

Begin by loading your late-hop addition into your empty fermentation vessel. Purge the fermentor with CO2, if possible, then add hot liquor at a target extraction temperature of 150–170°F (66–77°C). Let the hops steep for about an hour before you add the cooled wort and pitch the yeast. Make sure to adjust your gravity calculations to account for the extra liquid, watch your sanitization practices, and be careful to minimize oxygen pickup from splashing water or wort.

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