Bourbon Barrel Maintenance

This is another area where there is a lot of conflicting information, so I've gathered up my research here. This all seems to be correct and safe and won't ruin your barrel or your beer. Some of this applies to oak barrels in general, but my focus here is on bourbon barrels specifically.


About Barrels

Beer aged in used oak bourbon barrels takes on the characteristics of the bourbon and the oak, resulting in flavor complexity and possibly a fantastic beer. Bourbon is corn whiskey made in the United States and aged in charred, new oak barrels. Barrels used for bourbon are usually made of American white oak, as opposed to the French oak typically used for wine barrels.

The typical bourbon barrel holds 53 gallons, although there is some variation on size. Wine barrels usually hold 60 gallons (actually 225 liters, but close enough). Smaller barrels are available, with some distillers using 5 or 10 gallon barrels. These may or may not be charred, although bourbon barrels are always charred.


Purchasing a Barrel

New 5 and 10 gallon barrels (not charred) are available through most home brew shops. New barrels will give much stronger oak flavor in the first usage, and will mellow over time. Bourbon barrels are only used once for bourbon, but can be used over and over for beer.

Used bourbon barrels can be ordered online or through some homebrew shops. Distilleries may have used barrels available. The average cost seems to be around $160 for a used bourbon barrel. When selecting a barrel, there are a few things to look for:

• The metal hoops should be in good condition, not missing rivets or rusted through. Some rust is fine. The hoops should be snug on the barrel.
• The wood should not be overly detriorated.
• Residual bourbon in the barrel is good. It's best to buy a barrel that is still wet. 
• The bung hole should be sealed with a wood or rubber stopper, which keeps the inside clean and free of contamination.

Preparing to fill a bourbon barrel:

Drain off any residual bourbon. Invert the barrel and drain the bourbon through the bunghole. The residual bourbon will contain charcoal because the inside of bourbon barrels are charred. The residual bourbon will contain a fair amount of charcoal particles. Removing the residual bourbon serves to remove these charcoal particles, but you'll also end up with some bourbon that you can filter with a cheesecloth and drink or use as desired.

Rinse several times with clean water, drain thoroughly after each rinse. Fill the barrel completely and check for leaks. If there are leaks, keep the barrel full of clean water until the wood swells and the leaks stop. It should take no more than 10 days for the leaks to stop. If there is still leakage after that time, the barrel will likely need repaired or replaced.

Sanitize the barrel (see below). Locate the barrel in a cool, dry area, preferably 55F - 65F. Put the barrel on a stand so that it is well supported. Don't just let it sit on the side as this can damage the staves.

If desired, add a gallon of bourbon to the barrel and roll the barrel so that all sides are coated to help give the beer more bourbon flavor. Leave the bourbon in the barrel or not, your choice.


Filling a bourbon barrel with beer:

Don’t be overly concerned with preventing oxidation, as the beer will oxidize to a certain extent while aging in the barrel. Oak barrels are somewhat permeable to the outside air. However, there is no problem with purging the barrel with CO2 in order to prevent initial oxidation. It's always a good idea to place the end of the filling tube at the bottom of the barrel to prevent splashing, which is a major cause of oxidation.

Seal the bunghole with an airlock, just like you would for a fermenter. The beer will probably out-gas quite a lot in the first month or two. Once out-gassing has completed, a solid rubber stopper can be used.

Age the beer for a month to several years. Most microbreweries that age beer in oak barrels age the beer for 12 to 24 months, with 18 months being the average. Sample regularly (monthly) and drain the barrel into kegs or bottles when the flavor is where you like it. Oak flavors will be strongest in the first year and will mellow significantly in the second year.

There will be some loss of beer due to sampling and evaporation. Over an 18-month period, this can be as much as 5 gallons. Have additional beer ready to top off the barrel as needed. A cornie keg with a picnic tap is an easy way to top off the barrel.


Barrel Maintenance

While the barrel is filled, there really isn't any need for maintenance. There are some things to do while the barrel is being stored.


If stored empty:

• Rinse several times with clean water, drain thoroughly after each rinse.
• Place bung hole down for several days to completely drain.
• Stand barrel on end, leave bung hole open

Advantages: Easy to do.
Disadvantages: Barrel will dry and the staves will shrink over time, and will require extra preparation to swell the staves again and seal the barrel before transferring beer into it again. The hoops may come loose and will need to be reseated.


If stored wet:

• Rinse several times with clean water, drain thoroughly after each rinse.
• Fill with clean water.
• Insert a funnel into a rubber stopper, fit this into the bung hole, and overfill. Top up whenever the funnel level is low. This method keeps the inside of the bung area wet.

Advantages: Keeps the barrel swelled and ready to use.
Disadvantages: More maintenance.


Wet or dry, protect the barrel from freezing and from wide temperature variations. A constant cellar temperature of 55F - 65F is best.


If refilled immediately:

Used barrels require no special preparation beyond a simple water rinse, if desired, when transferring beer out and in immediately.


Sanitizing a Barrel

Sanitation can be a problem with oak barrels. Penicillium mold is the most common spoilage problem and can be difficult to eradicate. It is a blue-green fungus that may be visible around the bung hole. Typically, it will grow through joints or around the bung hole in barrels that have not been properly swelled. Other bugs that may grow in a barrel include acetobacter (especially in barrels that are not topped up regularly), brettanomyces (which can subsist on the  wood cellulose sugars in new barrels), lactobacillis and pediococcus.

To treat any of the above spoilage problems, make an alkaline solution, followed by an acid solution. For the alkaline solution, dissolve sodium carbonate or sodium percarbonate in a gallon or two of hot tap water. Use a mild solution (1 tsp per gallon of barrel volume) for general sanitation, or a stronger solution (3 tsp per gallon) for more severe problems.

For a 53 gallon bourbon barrel:
Mild: 1 tsp per gallon = 1 cup + 2 Tbsp
Strong: 3 tsp per gallon = 3 1/3 cup

Fill the barrel two-thirds full with water, add the solution to the barrel and then top up with water. Make sure to fill completely to wet the area around the bung hole. Let the barrel soak overnight, empty it and neutralize any remaining alkaline residues using a citric acid solution.  Prepare the citric acid solution by dissolving citric acid powder in one gallon of hot tap water. Use 1 tsp of powder per gallon of barrel volume (1 cup + 2 Tbsp for 53 gallons), again filling the barrel 2/3 full, add the solution, and top off. 

Sodium carbonate is the phosphate-free TSP that can be found in the paint department at Home Depot or Lowe's. 
Sodium percarbonate is Oxyclean and can be found at any grocery store.
Citric acid is available on Amazon for about $20 for a 5 lb bag of food grade powder.


Warnings:

Don't use StarSan in a barrel. 5-Star says not to use it on wood. I've seen several reports of people soaking their oak chips in StarSan, and getting a lot of gooey resin pulled out of the wood.

Other sources say to use 185F water as a pasturization treatment, and other sources say water over 150F will strip the oak flavors from the wood and can warp the staves. Using the alkaline/acid baths seem safest.


Holding solution (not for bourbon barrels):

A holding solution can be used to store a barrel wet. This is not recommended for new barrels, barrels less than one year old or barrels previously holding spirits such as bourbon since oak and other flavors would be stripped. Use a sulfur/citric solution to fill and store barrels. This holding solution will promote sanitation, keep the barrels swelled and smelling clean.

The holding solution is prepared using 0.5 oz of citric acid and 0.75 oz of potassium metabisulfite for each 4 gallons of barrel volume. (7 oz citric acid and 10 oz potassium metabisulfite for a 55 or 60 gallon barrel). Dissolve these in a gallon or two of hot water. Fill the barrel two-thirds with water, add the holding solution, top up the barrel with cool water, and bung the barrel. Top up the barrel with a holding solution once a month to replace lost solution. The barrel can be stored indefinitely without the risk of spoilage. During storage, rotate the barrel 45° in either direction every time you top up to keep the bung area soaked. (Or use the stopper and funnel method mentioned above.) This will prevent the bung area from drying out and protect it from spoilage organism growth. The holding solution will etch a concrete floor. Rinse the floor with water to prevent this.

Citric acid is available on Amazon for about $20 for a 5 lb bag of food grade powder.
Potassium metabisulfite is available at most homebrew shops since it is also sold as yeast nutrient.