Most oak kegs will arrive to you dry, and storage before or between uses is also usually done without liquid in the barrel. As a result, the wood will tend to dry and shrink when the keg is in storage, making it necessary to "cure" your barrel before use to ensure that the barrel is 'tight' and retains liquid. Failing to do so can result in lost product as it runs from the barrel almost as quickly as you pour it in.
Curing the barrel is a relatively simple process, but depending on what you intend to age it, can involve sterilizing the keg as a second step. Sterilizing the barrel is most commonly done when aging wine, as the lower alcohol content makes the product more likely to take on bacterial or fungal infections. The rather high proof of distilled spirits make this a non-issue, so providing the keg is generally clean inside it is acceptable.
Step 1: Getting the Wood To Absorb Water and Expand
What: The first part of curing your barrel is to force the wood staves to absorb water.
Why: This causes the staves to expand and tighten, closing the gaps between staves, which allows the keg to hold liquid without leaking.
How: Soaking the barrel in a tub of water is one option, however, if your barrel is finished, that is, it has stain or varnish, then this method can damage its appearance. A simpler option is as follows:
Place the keg in a sink or bathtub with the drain open and fill it with hot water from the tap. Doing this in a sink or bathtub allows the water running from the barrel to go down the drain, avoiding the exterior of the keg sitting in pooling water.
As the water runs from the keg, continue topping it up with hot water. Hot water tends to be absorbed by the wood more quickly, shortening this process. Keeping the keg topped up with water will also force the wood to absorb the water. Allowing all of the water to drain from the barrel will not force the wood to take on the water, and make this a very tedious project.
How long does it take? Depending on the dryness level of the wood this process can take anywhere from a few minutes to more than 24 hours. Smaller kegs, such as the 2 or 4L size, have smaller staves and therefore take less time to cure than larger kegs. This is because smaller staves require less water to expand than do larger staves. If you're curing a larger keg, hang in there--this is a proven technique that will efficiently tighten virtually any keg, so it will be worth your troubles!
Step 2: Testing the Oak Keg For Leakage
What: The second part of curing your keg is making sure that the wood staves have expanded enough to sufficiently hold liquid.
Why: You don’t want to wait until the keg is leaking the precious liquid that you intend to age in it! Try it out with water first so you don’t waste any of your efforts.
How: Once the keg appears to have only minimal leaking after completing Step 1, let it rest with the water overnight to ensure that it will hold liquid without leaking. You are then ready to drain the keg and add your spirit, or sterilize the barrel to prepare it to take on your wine for aging.
Don’t Skip Step 1!
It is important to note why the barrels should not be stored full of water to keep the wood wet and the barrel tight in the first place. Storing the barrel with water will result in mold issues, potentially rendering the barrel useless. One option is to add water to the barrel regularly and allowing it to sit overnight. This will keep the wood wet enough to have the staves remain tight, and reduce the time required to cure the barrel before use.
Sterilizing Your Oak Keg
Sterilizing the keg can be done in one of a couple of ways. The most common method is the burning of a sulfur strip in the barrel so that the sulfur dioxide emitted will kill bacteria, wild yeast, etc. A second option is to simply fill the barrel with very hot water (above 170 degrees Fahrenheit) and allowing it to sit for 30 minutes. The extremely hot water will sterilize the barrel without introduction of sulfur.