Hop Torpedoes Away
Sierra Nevada’s hop torpedo — a device the brewery designed for dry hopping beer — holds 150 gallons (570 L) of beer and up to 80 lbs. (36 kg) of whole hops. Beer is circulated through one or more torpedoes slowly for four days, ensuring that all the desired oils are extracted from the hops. The system is flushed with carbon dioxide before use to minimize the beer’s exposure to oxygen. The brewery’s Torpedo Extra IPA, named for the device, is dry hopped with whole hops — a mix of Crystal, Magnum, and Citra.
At first glance, they appear to be leftover props from an Ed Wood science fiction B-movie: long, slender metal contraptions with rounded tops, ready to transport aliens to earth on a seek-and-destroy mission. The only problem with this scenario is that it’s not an abandoned Hollywood set, but the Sierra Nevada Brewery, where these vessels are stored.
And while these mystery vessels may not be space-aged, they are certainly innovative devices for imparting hop character to beer. They are called hop torpedoes and are the latest in brewing innovation from Sierra Nevada founder Ken Grossman and brewmaster Steve Dresler. The idea for the device rose out of a growing desire, coupled with increasing consumer demand, for dry-hopped beers, including Celebration Ale and the Torpedo Extra IPA that is named after the device.
“We wanted to do something with post-fermentation hops, the dry hopping process, but stay with our historic philosophy of using only whole cone hops,” Dresler explains. “Most breweries that want to do a post fermentation hopping either use pellets or extracts or oils because they are easy to use and easy on how you handle the beer. We did not want to go that route. The question was, how do you get whole hop flavor and aroma into a beer without going from one tank to another and having (to utilize) hop bags?”
For years, Dresler explains, the brewery dry hopped with giant hop bags. But even after prolonged soaks, the center of the bags typically contained dry or marginally damp hops that never really touched the beer. This poor saturation resulted in an under utilization of the volatile hop oils. Dresler knew there had to be a better system than a passive soak. The plan was to come up with a way to circulate the beer through large beds of hops.
“As we were discussing these things in meetings, Ken got together with tank fabricators and was describing things on the phone and drawing pictures on napkins,” Dresler recalls. “All of a sudden we have this upright tank with proper fittings and a manway on top to hold the hops in place. We did some in-house modifications and voilà, there you have it. It’s nothing unique or fancy. It’s basically a small tank you hook up to a big tank.”
How it works
It’s what goes into the small tank that counts, hops, hops and more hops — up to 80 lbs. (36 kg) per vessel. Here’s how it works: the vessel, which holds 150 gallons (570 L) of liquid, is filled with hops and then the beer from the fermentation tank is slowly pushed through it. The beer is then pumped back to the main tank. At the beginning of the circulation, the beer is at fermentation temperature (68 °F/20 °C), carbonated and may still have some yeast in suspension. Depending on batch size, typically between 100 and 400 barrels, the beer might pass through two torpedoes before returning to the main tank. The circulation continues — at a rate of 3 gallons per minute (11 L per minute) — for four days, during which the beer is chilled. Prior to circulation, the loop is flushed with carbon dioxide (CO2) to minimize the amount of oxygen coming in contact with the beer.
“That’s really all it is,” Dresler said with a laugh. “We slowly circulate the beer through this vessel and back into the tank in the loop, and by doing so we very passively extract the volatile oils from the hops. But we do so much more effectively and efficiently than you can by having the teabag approach. We’re using everything we can get out of the hops.”
The torpedo is similar in many ways to a hopback (or hop jack). A hopback is a vessel that lies between the kettle and the heat exchanger. Hopbacks are packed with hops and hot wort flows through them, quickly extracting water-soluble hop oils. The wort is then chilled and fermented.
In contrast to a hopback, the torpedo is used on the cold side and extracts both water-soluble and alcohol-soluble compounds from the hops. The contact time required for the torpedo is much longer than with a hopback, and the hop oils extracted in the torpedo encounter far fewer yeast cells and do not experience a vigorous primary fermentation.
The other hop-extracting device with obvious similarities to the torpedo is the Randall. Developed by Dogfish Head, the Randall is a large canister that sits on the line between keg and tap. It is filled with hops and when a beer is drawn, it travels first through the hops, picking up some of the hop oils. Both the torpedo and the Randall filter carbonated beer through a bed of hops. The primary differences are the extended contact time with the torpedo and the fact that the beer is circulated through the device repeatedly, whereas the beer makes a single pass through the hop bed in a Randall.
Torpedo Extra IPA
The result is an IPA with an intense hop aroma. The key, Dresler says, is total saturation that allows almost 100 percent utilization of hop oils, which in Torpedo Extra IPA is a combination of Crystal, Magnum and Citra.
Citra is a new hop variety that has a unique flavor profile, showing hints of gooseberry, passion fruit, lychee, grapefruit and lime. If you wish to try the clone recipe, on the facing page, you will likely have trouble finding this variety as it is new. If you can’t locate a source, Amarillo may be the best substitute.
Even with 70 IBUs of bitterness, the beer does not come across as harsh, because the bitterness is backed by ample hop flavor. Although the focus of the beer is on the hops, there is just enough malt presence to make it a balanced brew.
“We can analyze the beer as we’re doing it,” Dresler says. “Eventually the hop oils flat line, but it’s not because the beer is saturated, but that we’ve extracted the entire amount out of the hops.”
Dresler says mastering the IPA took about two to three years, and there were a number of challenges. One was making sure the beer was well blended. This was accomplished by setting the return pipes higher in the beer.
“You’re basically drawing out of the bottom, going through the hops and returning to the tank through the bottom but at a higher level,” Dresler said. “We didn’t want to saturate the beer with hop oils at the bottom, but by introducing the beer back higher in the tank we get a better mixing and blending as well.”
Dresler also needed to fine-tune a recipe that would work well in conjunction with the vessel. The malts and boil hops were the easy part in creating this 70 IBU, 7.2% alcohol by volume (ABV) beer, he says, it was balancing the post fermentation hops that needed a lot of tweaking — something he seems to enjoy.
“I can modify the hops I’m using in the torpedo vessel to construct layers of aroma and flavor by having a quantified approach to it,” he says.
“Different varieties of hops have different levels of volatile oils, so when I’m going to use the torpedo I’ll rub the hops and get an idea of what hops and what percentage I want to use to end up with a really nice dry-hopped beer.”
“But we’ve also learned that, depending on the temperature and the flow rate, you tend to extract these compounds at different times in the process,” he added. “Some aromas come off very early in the circulation in the torpedo, some a little later. As we’ve developed this, we’ve learned when to hook up to the tank depending on what we want, how long we want to circulate, at what rate and at what temperature. We use all of this information to develop unique aroma profile. You can really develop some nice nuance and flavors with it.”
Dresler notes that all the monitoring offers one other advantage, knowing when to cut the flow to prevent off flavors.
“We monitor everything closely,” he says. “You can over circulate through the vessel and get more of a grassy, stemmy-type note. We now know when to cut that off. You take the positive attributes that give more floral notes. You’re leaving some stuff behind, but it’s stuff you don’t want.”
Dresler adds that even filtering of the Torpedo Extra IPA is reduced to prevent stripping any of the crucial hop aroma.
“We’re willing to sacrifice some of that beer clarity for enhanced flavor, aroma and mouthfeel. We’ve left all that original hop flavor and aroma intact,” he said.
“Quality of hoppiness and aroma is something we’re very proud of here.”
A Homebrewed Torpedo?
For the homebrewer wanting to produce this beer, the biggest difficulty, naturally, would be emulating the torpedo. While certainly not against the idea of a homebrewer using something like a torpedo device, Dresler questions the need, especially when considering that homebrewers are not under a production constraint and can leave the hops on the beer for as long as one chooses. Plus, most batches tend to be relatively small.
“One of the things with homebrewing, most of the vessel sizing is relatively small,” he says. “The teabag method tends to work really nicely and efficiently at this level.”
Even if a homebrewer fabricated a torpedo-like device, Dresler says circulation becomes the real issue since most homebrewers rely on gravity.
“The ability to pump and circulate would be the most difficult part,” he says. “But, if you can set up a pumping system in your homebrew system where you can go from a vessel into another vessel and back to another and have a canister of some type, like a filter housing, you could put hops in there and slowly pump the liquid through it. That would be kind of a way to emulate the same effect. It would be difficult at home, but if you’re the gadget type of guy, it would be kind of a fun challenge to see what you can do.”
One possibility for a set-up to emulate the effect of a torpedo could be assembled by almost any homebrewer who kegs his beer. If you had three Cornelius kegs, you could push beer with CO2 pressure from one keg to another, with a keg in the middle serving as the torpedo. For this, you would hook up the full keg to the torpedo with a tube connected from the “beer out” post on the full keg to the “gas in” post on the torpedo. The torpedo would be, in turn, connected from its “beer out” post to the “beer out” post on the receiving keg. A final tube would extend from the “gas in” post on the receiving keg into a glass of water. This would serve as a gas trap, to relieve pressure on the receiving keg without letting oxygen in. The center keg — the torpedo — would contain whole hops in a dry hop bag. The torpedo and receiving keg could be flushed with CO2 prior to pushing the beer. The full keg would, of course, be connected to your CO2 tank and should be connected to the torpedo last, so that beer doesn’t start flowing before you’re ready. You may also want to let some beer build up in the torpedo before letting it start to flow into the receiving keg. This will prevent you from pushing foam from the torpedo. Beer could be pushed through the hop bed several times by simply reversing the connections once the receiving keg is full.
For the hop-headed homebrewer or inveterate gadget guy, a homebrewed torpedo could add a twist to your IPA.
Recipes
Sierra Nevada Torpedo Extra IPA clone
(5 gallons/19 L, all-grain)
OG = 1.070 FG = 1.018 IBU = 70 SRM = 11 ABV = 7.2%
Ingredients
14 lbs. (6.4 kg) pale malt
11 oz. (0.31 kg) caramel malt (60 °L)
17 AAU Magnum hops (60 mins)(1.2 oz./34 g of 14% alpha acids)
1.0 oz (28 g) Magnum hops (5 mins)
1.0 oz. (28 g) Crystal hops (5 mins)
0.67 oz. (19 g) Magnum hops (dry hop)
0.67 oz. (19 g) Crystal hops (dry hop)
0.67 oz. (19 g) Citra hops (dry hop)
Wyeast 1056 (American Ale), White Labs WLP001 (California Ale) or Fermentis US-05 yeast
1 cup corn sugar (for priming)
Step by Step
Mash at 152 °F (67 °C). Boil for 90 minutes, adding hops at times indicated. Ferment at 68 °F (20 °C). Dry hop for 10 days to 2 weeks or use a torpedo to add hop character.
Sierra Nevada Torpedo Extra IPA clone
(5 gallons/19 L, partial mash)
OG = 1.070 FG = 1.018 IBU = 70 SRM = 12 ABV = 7.2%
Ingredients
3 lb. 5 oz. (1.5 kg) pale malt
11 oz. (0.31 kg) caramel malt (60 °L)
4.0 lbs. (1.8 kg) light dried malt extract
2 lb. 4 oz. (1.0 kg) light liquid malt extract (late addition)
17 AAU Magnum hops (60 mins)(1.2 oz./34 g of 14% alpha acids)
1.0 oz. (28 g) Magnum hops (5 mins)
1.0 oz. (28 g) Crystal hops (5 mins)
0.67 oz. (19 g) Magnum hops (dry hop)
0.67 oz. (19 g) Crystal hops (dry hop)
0.67 oz. (19 g) Citra hops (dry hop)
Wyeast 1056 (American Ale), White Labs WLP001 (California Ale) or Fermentis US-05 yeast
1 cup corn sugar (for priming)
Step by Step
To get the proper amount of hop bitterness, you must be able to boil 4.0 gallons (15 L) of wort. Mash grains at 152 °F (67 °C) for 45 minutes. Collect wort and add water to make 4.0 gallons (15 L). Stir in dried malt extract and bring wort to a boil. Boil for 90 minutes, adding hops at times indicated. Add boiling water if wort volume drops below 3.5 gallons (13 L). Add liquid malt extract for final 15 minutes of the boil. Ferment at 68 °F (20 °C). Dry hop for 10 days to 2 weeks or use a torpedo to add hop character.
Sierra Nevada Torpedo Extra IPA clone
(5 gallons/19 L, extract with grains)
OG = 1.070 FG = 1.018 IBU = 70 SRM = 12 ABV = 7.2%
Ingredients
1 lb. 5 oz. (0.6 kg) pale malt
11 oz. (0.31 kg) caramel malt (60 °L)
5.0 lbs. (2.3 kg) light dried malt extract
2 lb. 6 oz. (1.1 kg) light liquid malt extract (late addition)
17 AAU Magnum hops (60 mins)(1.2 oz./34 g of 14% alpha acids)
1.0 oz (28 g) Magnum hops (5 mins)
1.0 oz. (28 g) Crystal hops (5 mins)
0.67 oz. (19 g) Magnum hops (dry hop)
0.67 oz. (19 g) Crystal hops (dry hop)
0.67 oz. (19 g) Citra hops (dry hop)
Wyeast 1056 (American Ale), White Labs WLP001 (California Ale) or Fermentis US-05 yeast
1 cup corn sugar (for priming)
Step by Step
To get the proper amount of hop bitterness, you must be able to boil 4.0 gallons (15 L) of wort. Steep grains in 3 qts. (~3 L) of water at 152 °F (67 °C) for 45 minutes. Add water to make 4.0 gallons (15 L), stir in dried malt extract and bring to a boil. Boil for 90 minutes, adding hops at time indicated. Add boiling water if wort volume drops below 3.5 gallons (13 L). Add liquid malt extract for final 15 minutes of the boil. Cool wort and transfer to fermenter. Add cold water to make 5 gallons (19 L). Pitch yeast and ferment at 68 °F (20 °C). Dry hop for 10 days to 2 weeks or use a torpedo to add hop character.
