Prepping Used Barrels for Aging Beer

Here are three things you need to know about prepping a barrel for aging beer.

Dave Carpenter Apr 3, 2016 - 8 min read

Prepping Used Barrels for Aging Beer Primary Image

Wood-aged beer has become a signature feature of craft breweries across the country, and homebrewers have discovered the beauty of the barrel as well. While it’s often impractical for solo homebrewers to fill an entire 50–60-gallon (189–227-liter) barrel, homebrew clubs regularly employ the divide-and-conquer method, in which several members brew and ferment similar recipes before blending their contributions in one or more community barrels.

To learn more about barrels, I turned to two brewers from completely different Portlands. Hair of the Dog Brewing Company in Portland, Oregon, is well known for its unusual lineup of diverse beer styles, many of which are barrel-aged. Founder and Brewer Alan Sprints currently nurtures almost 200 barrels at Hair of the Dog.

Meanwhile, across the country in Portland, Maine, Allagash Brewing Company has been crafting Belgian-inspired ales for almost exactly the same amount of time and has operated a highly respected barrel program since 2004. Brewmaster Jason Perkins oversees a vast portfolio that includes a series of spontaneously fermented beers that begin life in the brewery’s coolship.

So when I asked Alan and Jason for some tips on barrel prep, I was pleased to learn that you can pretty much avoid the chore altogether if you do just three things:

  1. Stick to freshly emptied barrels.
  2. Use spirits barrels for clean beers.
  3. Use wine barrels for sour beers.

Yes, it can certainly be more complex than that, especially if you want to work with brand-new barrels. But if you take these tips to heart, the inside of your barrel might never need to see a scraper.

Fresh Is Best

“I get barrels that have been freshly emptied,” says Alan. Ideally, you want to fill your barrel with beer immediately after it has parted ways with its former occupant because an empty barrel will start to dry out. And as wood dries, it shrinks, which means the staves will contract, and the barrel will probably leak when you fill it. Unfortunately, homebrewers don’t always enjoy the same supply chains as the pros, which means you may very well find yourself having to resurrect a leaky barrel.

Making a leaky barrel watertight again usually means filling it with hot water. Jason uses a sophisticated spray-head system to saturate Allagash’s barrels, but homebrewers can simply pour in hot water and slosh. Most of this hot water will leak right out at first, but repeated attempts will begin to hydrate the wood. As the wood absorbs water, the staves will swell, and after a while, you’ll have a leak-proof vessel once again. This process, however, washes away some of the barrel’s character—be it woody, vinous, or spirituous—so rehydration is a process best avoided.

Rather than let a barrel dry out, if it’s not convenient to fill your barrel straight away, then at least keep it hydrated while it awaits your next brew. Get a handle (1.75 liters) of the appropriate liquor (or water for wine barrels), add it to the barrel, and roll the cask around to ensure contact with all surfaces. Continue to swirl and swish every couple of days until you’re ready to fill the barrel with beer. Keeping the barrel hydrated will prevent leaks and ensure that when it comes time to fill it, you won’t have to suffer the indignity of watching your homebrew trickle from between loose staves.


In Craft Beer & Brewing’s Wood Aging Your Beer class, you'll learn how to use wood for its unique flavor contributions, as well as for its ability to host a wide range of souring microorganisms. Sign up today!

In Good Spirits

Spirits barrels are those that have held whiskey, tequila, rum, brandy, and—rarely but increasingly—gin and vodka. Wood gives barrel-aged spirits their beautiful amber color (all spirits emerge colorless from the still), as well as pleasant notes of vanilla and coconut. When you age beer in a spirit barrel, the beer takes on the flavors and aromas of the spirit itself, as well as some woody overtones from the barrel.

The nice thing about spirits is that they’re high in alcohol, which means that the barrels they inhabit are more or less devoid of microscopic life forms. As Alan bluntly phrases it, “Spirit casks are clean, and wine barrels are dirty.”

Your typical barrel absorbs about a gallon of spirits into its wooden walls, which renders the staves inhospitable for spoiling microbes. Consequently, a whiskey barrel is the perfect vessel for aging clean beers that benefit from some additional flavor infusion: The trifecta of imperial stout, bourbon, and oak is classic for a reason, but tequila añejo barrels deliver a spicy punch that can work wonders for a wheat beer.


You can, of course, age a sour beer in a spirit cask. Jason from Allagash says that “barrels are an ingredient just like anything else.” So if you want some of that spirit character in your sour beer, there’s no reason not to age it in a spirit barrel. Just remember that you’ll probably need to inoculate the barrel with your own bugs, since the alcohol will have prevented any critters from gaining a foothold.

Sour Grapes

Used wine barrels make excellent sour and wild beers for at least three reasons:

  1. Wine has a mellower flavor than spirits, so wine barrels let the beer shine (whiskey or rum barrels might steal the spotlight).
  2. Wine is low enough in alcohol that bugs such as Brettanomyces and Lactobacillus can survive within the staves. Indeed, Brettanomyces growth is one of the reasons that winemakers have to retire their barrels after a period of time.
  3. Unlike, say, a bourbon cask (which by U.S. law can be used exactly once to age bourbon), vintners often refill wine barrels several times. Repeated batches of wine draw out much of the wood’s raw character before it accepts your beer.

Furthermore, wood is porous and admits a slow trickle of oxygen over time. That oxygen, along with certain sugars within the wood itself, provides a cozy environment for Brettanomyces. Even beers that aren’t Brett-dominant usually benefit from the manner in which Brett metabolizes by-products of the other bugs.

Remember, a whiskey barrel can go sour, but a sour barrel can never truly revert to clean. Microorganisms infiltrate the wood up to a depth of almost a centimeter, which is far deeper than you’d ever be able to effectively sanitize without destroying the barrel in the process. So rather than attempt to clean a “dirty” barrel, do as the Belgians do and turn it into a dedicated inoculation tank that guards your own secret blend of house yeasts and bacteria.

Make It Your Own

Of course, much of the fun of homebrewing is that there are no rules. Want to sour a beer in a whiskey barrel? Go for it. Looking to infuse a bit of Gewürztraimer character into your imperial wheat? Why not? Just remember to keep your barrels moist and be willing to accept whatever your microbes throw at you. And as long as you take good care of your barrels, they’ll take good care of you.