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Use and Care of Oak Barrels for Aging Beer

03/07/2014 12:38 PM | Anonymous
Use and Care of Oak Barrels for Aging Beer
by J. Frey, F.H. Steinbart Co.


Oak barrels are widely used in wine making and the spirit industry for the flavor they impart as well as their effect on the aging process. Brewers and breweries have recently grown fond of using oak barrels for similar reasons, but the nature of an oak barrel’s use for beer is a bit different. Brewers typically (but not always) age beer in a barrel previously used for spirits or wine. Beers aged in these barrels pick up the essence of the beverage previously contained in the barrel as well as oak flavor. Depending on how the barrel was handled, sanitation and preparation practices can be different from those used for new barrels.

The flavors imparted by oak range from smokey, tannin/tannic, toasted/charred to smooth, rich chocolate and/or vanilla and of course, woody. The type of oak used and the level of toast determine the flavors imparted in the aged beverage. In my experience, American oak provides a more wood-forward flavor. The tannins are high impact, lending crisp woody characteristics. French oak is known for its smooth and soft flavor impact. When I am looking for the classic vanilla-like oak flavor and aroma notes, I look to French oak. Please note that these are “nutshell” descriptions based on my personal experience and much more can be learned about the flavors imparted by various oak origins and toast levels.

The major factors governing how much flavor is imparted are the amount of time that the beverage is left in contact with the wood, as well as the ratio of total oak surface area to amount of beer in contact with that surface area. When adding oak pieces to a container of beer, one can increase the amount of oak used to decrease the contact time necessary to extract suitable flavor. For barrel use this means that smaller barrels impart flavor faster than larger barrels. This is because a larger barrel has a lower ratio of surface area to volume than a smaller barrel. Barrel aging also imparts subtle oxidation to a beverage overtime, and this effect is accelerated in smaller barrels, just as the flavor impact is. It is also important to remember that a barrel will impart significant flavor in the beginning of its life, but will impart diminishing amounts of flavor with consecutive uses.

Prepping a new barrel for its first use:

A new barrel from a reputable supplier should be biologically sound and only needs to be swelled with clean water to tighten the joints in the pieces of wood and prevent leakage. If you need to clean a used barrel, refer to the cleaning procedures below before filling the barrel.

The hot water method for swelling a new barrel is recommended because it uses less water thus stripping out less oak flavor in the process. Follow these steps:
  1. Fill the barrel with clean hot, steamy water to 20% capacity. Hot water and vapor will swell the staves of the barrel faster than cold water.
  2. Insert the bung and slosh the water around the entire surface of the barrel. Agitate the water inside the barrel until any leaky areas in the sides seal up and stop seeping water.
  3. Stand the barrel on one end and allow the head (the round, flat end section) to swell until it stops leaking. Flip the barrel and allow the other head to swell.
  4. Place the barrel bung-down to allow the water to drain thoroughly. Allow the barrel to cool down and dry adequately before immediately filling with your beverage of choice.
The cold water method will seal most problematic leaks and is recommended for barrels that have been stored dry for extended periods of time. Since this method uses more water for longer contact time, more flavor will be stripped from the barrel than when using the hot water method.
  1. Fill the barrel completely with cold, clean water and soak overnight. This should be done above a floor drain or somewhere that you wouldn’t mind water leaking onto the ground for a day or two.
  2. Add one campden tablet (crushed) per 20 gallons of water to neutralize any chlorine in the water.
  3. All reasonable leaks should seal up overnight or in a few days. Water should never be left in the barrel for more than 48 hours to avoid mold or bacteria growth. If more than 48 hours soak time is needed to seal any leaks, the barrel should be drained and refilled with fresh water.
  4. When all leaks have sealed, place the barrel bung-down and drain thoroughly before immediately filling with your beverage of choice.
Most brewers prefer to use freshly drained spirit or wine barrels to age beer, because it also imparts the essence of the previous beverage. If the barrel is filled with beer almost immediately after the draining of the original beverage, and the barrel is properly handled, it will not need to be cleaned before filling. If the previous beverage is biologically sound, then the barrel is sanitary as well. If the previous beverage is contaminated (in the case of wine) it is impossible to remove the bacteria completely because contaminants can hide deep in the crevices away from cleaning procedures.

Since it is not always possible to fill the barrel with beer immediately after draining, it is sometimes necessary to store the barrel either dry or with a storage solution. Storing the barrel dry with the proper method is recommended because it will strip fewer flavors than the storage solution method. The dry storage method is as follows:
  1. After draining the barrel, rinse it several times with hot, then cold water and allow it to drain thoroughly.
  2. Place the barrel bung-side-up and insert a sulfur stick burner with 5 grams of burning sulfur stick per 60 gallons barrel capacity. A sulfur stick burner can be purchased or made at home. It consists of an apparatus to hang a flameproof cup inside the barrel and the cup itself, which needs to hold/hang the burning sulfur-stick and also catch the ashes and prevent them from depositing into the barrel. Most sulfur-stick burners also have a bung to close off the barrel and contain the sulfur gas inside. Think of a coat hanger, a small steel cup, and some ingenuity. Sulfur-sticks should be burned outside in a well ventilated area because sulfur gas is harmful to breathe.
  3. After burning the sulfur-stick, bung the barrel tightly to trap the sulfur gas inside. Store your barrel in a sound environment at the proper humidity. The sulfur-stick treatment should be repeated every six to eight weeks to replenish the antimicrobial effect of the gas. 
It is possible to store your barrel wet with a storage solution. The downside of this is that oak flavor will be stripped from the barrel as you store it. The upside is that the barrel can be stored for longer periods of time without continuous care, and there is less risk of the barrel drying out. Barrels kept full of storage solution will not need to be checked for leaks/swelled before filling with beer. The steps are as follows:
  1. Calculate your storage solution chemicals needed for your barrel capacity; 1 gram of citric acid and 2 grams of So2 powder per liter of barrel capacity. This solution can be corrosive to metals and can etch concrete floors. Be judicious with its use and wash up residual amounts that may spill.
  2. Fill the barrel half-way with cold water.
  3. Mix up your chemicals needed into a few liters of warm water until everything is dissolved. The fumes of this solution are abrasive and harmful to breathe, so do this in a well ventilated area.
  4. Add the chemical solution to the barrel, mix thoroughly and top the barrel up to capacity with more cold water. Bung the barrel securely.
  5. You will need to top up the storage solution periodically depending on evaporation rates.
  6. This solution will need to be replaced eventually, but it is hard to say how often. A good rule of thumb would be quarterly (every 3 months).
Barrel aging has a profound effect on the beer stored inside the barrel. Aside from the flavors introduced, barrel aged beers develop superior body and “structure,” in part from the concentration of flavors through evaporation. The slow exchange of oxygen through the walls of the wood lend a controlled maturation. Although the oak flavor contributed by a barrel will be completely spent in about 3-4 uses, the barrel will continue to offer its “structuring” benefits. Barrels that have lost most of their oak flavor can be “refreshed” by adding new oak pieces through the bung. The best determining factor in how long to leave your beer in the barrel is taste. As discussed earlier, smaller barrels impart flavor and other benefits faster than larger barrels. Over generations upon generations of wine and spirit makers and countless vintages of wood aged beverages, professionals have decided upon 30-60 gallon sized barrels as an ideal size for aging. Decisions about the aging process are done intuitively, and it will take some experience to gain an appreciation for the details of barrel aging. It is recommended to save a portion of un-oaked beer outside of the barrel to preserve the possibility of blending back in to the oaken beer, affording you the option of balancing the oak flavors in the direction of less oak. In this way, beer can always be left on oak for longer to develop more of its benefits, and in the case of mild “over-oaking” it can always be blended back into perfect balance.

Barrel spoilage:

With proper care and attention to detail, your barrel will provide you years of use. Visible mold growing on the outside of the barrel is relatively normal from time to time, but should be cleaned in a timely manner to avoid the growth of the problem penetrating the spaces between the staves, eventually working its way to the inside of the barrel. These problem areas should be scrubbed with a coarse brush and a solution made in the manner of the storage solution outlined above (1 gram of citric acid and 2 grams of So2 powder per liter of water). Take care not to leave the solution in contact with the metal hoops of a barrel to avoid corrosion of the hoops.

Unfortunately, a contamination issue left ignored for any period of time will render your barrel unusable. Bacteria can reside deep in the crevices of the wood, safe from the reach of our cleaning methods, only to emerge later and contaminate the next batch of beer introduced to the barrel. Proper sanitation methods combined with the proper barrel care outlined in this article will ensure a minimum of contamination issues for the life of your barrel. Under a worst-case scenario, a barrel can be sent to professional for a service in which the inside of the barrel is scraped, exposing new oak and re-fired to renew the toast to the wood. This can eradicate minor contamination but not well established colonies of bacteria. A confirmed brettanomyces contamination is said to be permanent in the wood, and these barrels should not be further used to age beer unless the bacteria is desired in the flavor profile. They make great decorations, furniture, or planters. Alternatively, you could dive into the murky depths of sour beer brewing (another topic reserved for another article).

With proper care and a little luck your barrel will provide years of trusty service. Employ steadfast attention to detail to limit contamination to an absolute minimum and you will "WOW" your friends and peers with beers as complex and high-impact as the super limited, wait-in-line, $20 per-bottle, wax-dipped, hand-numbered super beers that we are all so familiar with in this town!

Thanks for reading and cheers!

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