Dressed in a cowboy hat and plaid shirt and wrapped in his Woody Guthrie persona, Sam Calagione, founder of Milton, Delaware’s Dogfish Head Brewery, couldn’t help but keep grinning as he introduced his 120 Minute IPA to an audience of brewers who showed up at d.b.a. Pub in New Orleans during the 2003 Craft Brewers Conference to drink his beer and listen to him channel Guthrie.

“See what we did, we plated our yeast strains—this is probably the only time I’ll get to describe this and everyone will understand what I am saying—we plated our yeast strains,” he said gesturing with his right hand as if he were spreading icing across the top of a cake. “And we looked under that microscope. And we saw all these little yeast strains and they had all this little leather on.”

He put his hands to his hips and wiggled. “And little whips and chains and shit.” He lifted his right hand and cracked an imaginary whip. “And they were beating the [tar] out of each other.”

The result, Calagione said, was a beer with 20.4 percent alcohol, still grinning and knowing full well that brewing a super-high-gravity beer is not quite that simple.

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A little more than twenty years ago, beers such as Thomas Hardy’s Ale (12 percent) and Hürlimann’s Samichlaus (14 percent) were thought to present an upper limit. But now, professional craft brewers and homebrewers are pushing alcohol beyond the speed of sound.

“A lot of [homebrewers] are afraid to try it,” says The Bruery Head Brewer Tyler King, who has shared the secrets of brewing high-gravity beer in presentations to homebrewers. Homebrewers, in turn, have shared their beers with him. “They bring me bottles—they sometimes get higher alcohol than we do. It’s kinda cool to see them do it.”

It doesn’t necessarily get easier over time. “We’ve been doing this ten years and we are still learning,” says Adam Avery, founder and president of Avery Brewing in Boulder, Colorado, also a pioneer in brewing high-alcohol beers. “There are so many variables. We still throw away the occasional batch.”

He describes it as the most scientific brewing Avery does, but possibly the most insane amount of work. “It takes a lot to keep the yeast alive,” he says. “It’s like a triage unit trying to get the victim to the end of the road.”

Avery first brewed The Beast, now an annual release that contains between 15 and 17 percent alcohol, in 2003 and released it in 2004. It was the initial beer in what became “The Demons of Ale” series. “A lot of yeast strains can get you to 12 percent. After that you need to help them,” Avery says. At Avery, the help includes using glucoamylase, a starch-digesting enzyme that some people take to aid digestion or for other health reasons. That’s not classified information, but Avery would rather not share the complete details about how it is implemented. “These secrets were hard-earned,” he says.

Besides, he says, how much to use and when to add it are just two of many variables the brewers at Avery monitor carefully. The rest of the list is rather basic—much like one The Bruery in Southern California uses—and focuses on things such as osmotic pressure, yeast strains, temperature control, oxygenation, and pH levels, parts of the fermentation process that many homebrewers don’t fully appreciate. “I find many homebrewers focus on the brewing side and not enough on the fermentation side,” King says. “It’s hard to wrap their heads around.”

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The Bruery Founder Patrick Rue and King had a sense of what they needed to do but not totally how they would do it the first time they brewed a batch of Black Tuesday, their 18 percent-plus barrel-aged imperial stout. Although the beer is released once a year in October, they brew it at least once a month, sometimes twice, the batches aging a year or more before they are blended for the next release, allowing the brewers to refine the process. Here are their tips for brewing high-gravity beer.

Keep osmotic pressure low.

Osmotic pressure is the force that develops between two solutes of differing concentration separated by a semi-permeable membrane (such as a yeast cell wall). Very high osmotic pressures, such as those encountered in high-gravity worts, can distort yeast metabolism and decrease viability. The initial osmotic pressure placed on the yeast will affect the physiology of the cell until the end of fermentation, and everything The Bruery does is with that in mind.

To keep the osmotic pressure low, shoot for an original gravity no higher than 1.106 (25° P). Keep adjuncts out of the brewhouse, but add them gradually during fermentation, daily or in smaller doses multiple times a day. Adjuncts don’t contain nutrients, so add yeast nutrients (such as Yeastex) with each sugar addition. Although sugar should be your primary adjunct, high-gravity professional brewers also get creative and add other types of fermentable sugars into their worts. For instance, in July, King had just finished brewing Autumn Maple, a seasonal for the fall made with yams, spices, and maple syrup. He used the leftover syrup to feed barrels of Black Tuesday. “Every year [when it is time to blend], the barrels that include the maple syrup are the best batches,” King says.

Use the right yeast strain.

Obviously, brewers need to use a yeast strain that has a high alcohol tolerance and that is very attenuative. The Bruery’s house strain is proprietary (“the thing is a beast”), but King says it is similar to Belgian strong-ale strains. He warns brewers should resist the urge to over pitch, aiming for 15–20 million cells per milliliter if the original gravity is 1.106 (25° P).

Keep the fermentation ­temperature low.

Regardless what the yeast producer suggests, start with the fermentation temperature in the mid-60s (64–66°F/18–19°C) at the outset and monitor it throughout. (See “Homebrewing Lagers: Chilling Out” for tips on keeping fermentation temperatures low.)

Keep oxygen levels up.

Because yeast needs oxygen to do its work, you need to keep oxygen levels up. (Larger breweries with the necessary measuring equipment will target between 9 and 15 parts per million). Keeping oxygen levels up is particularly important in the first 24 hours after fermentation starts. “Shaking the wort before pitching is not enough,” King says. He suggests oxygenating every day for the first 3 to 6 days or each time sugar and yeast nutrient are added. Homebrewers can use aquarium stones or compressed oxygen cannisters for oxygenation.

Monitor the pH.

Use brewing salts to assure the wort pH is between 5 and 5.3. With proper aeration and the addition of nutrients, it should remain between 4.5 and 5 during fermentation, falling as it nears completion.

Agitate the wort regularly.

The Bruery uses pumps to recirculate the wort during fermentation. This delivers nutrients that the yeast needs right to the cell wall, keeps yeast from flocculating, and eliminates carbon dioxide, which is toxic to yeast. King acknowledges that few homebrewers have comparable equipment but suggests that the work involved shaking a carboy or fermentation bucket is worth the physical effort.

Finally, King stresses patience. “It’s a big beer and has to sit for a while,” he says. “It can taste bad out of the fermentor and bad anywhere from 6 months to a year.” Black Tuesday ages for a year, most of the time in used bourbon barrels. The barrels are blended to create the final beer, and if one tastes too young, it will be held back for a year.