When whiskey is your business, few things are more disappointing than losing precious spirit to something as simple as a leaky barrel. Some loss is inevitable: Angel’s Share (or evaporation) will always claim its toll, but that’s the price we pay for aging in new oak barrels. Other losses can be stopped if you catch them in time though. We caught up with Kevin Curtis, Angel’s Envy’s Distillery Operations Manager, to learn more about the basics of barrel repair and maintenance.

Kevin Curtis

What can cause leaks? What are some of the more common types that you have to deal with?

Well, to start with, barrels can have wormholes. As the staves are being cut from the log, there might be trails through the wood from an insect from who knows how long ago. They can be easy for a cooper to miss because they don’t normally show themselves during the quality testing performed at the cooperage. Before aging bourbon, the barrels are pressure tested with water. This can weed out some of the clearly flawed barrels suffering from leaking seams, cracks, knotholes, warps, etc. But when a barrel is used to age whiskey, things can change. Alcohol is a better solvent than water and can erode those holes in a way that water can’t. That’s certainly one way to get a leak.

You can also have cracks in the wood, sometimes around the bunghole—which it should go without saying should always be stored facing up. Obviously if a barrel is dropped or handled roughly at any point, you run the risk of splits. There can also be a leak between the staves in a seam if a stave isn’t perfectly planed, or if the barrel is dropped on its chime (the edge of the barrel at the head). The staves of the barrel are normally bent using steam or heat to make them more flexible as the hoops are put on. Cracks can develop during the bending process, too.

Barrels can split as they heat and cool. Different staves absorb fluid at different rates, based on the wood’s density, causing them to shrink and expand at different rates. Heads and staves will occasionally warp from these variations. There might also be a knot that the cooper didn’t see, and that can cause a weak spot. There’s a lot of stress on a barrel as the spirit ages, and it increases every year as the whiskey flows into and out of the wood.

So how do you repair leaking barrels? What kinds of tools and techniques do you use?

We use a few specialized tools: cedar wedges and spiles (little plugs), punches, hoop drivers and a cross peen hammer for repairing barrels. If I have a small pinhole leak from a wormhole or small knot, I’ll use a sharpened punch to widen the hole and then a cedar spile. For seam leaks or cracks, I’ll use a knife to score a channel next to the seam and then hammer a cedar wedge into that, sealing it all up. Occasionally we’ll need to tighten up the hoops with a hoop driver—that can help.

If you get a leak around the head, sometimes we’ll put cattail reeds between the staves at the head. It requires removing the hoops, which is much trickier to do when there’s a lot of whiskey in the barrel. You can also pop out a head and replace it with another if you know what you’re doing. You just stand the barrel up, pop the top couple of hoops off, pry the old head out and put in a new one. It is easier to do on an older barrel. They tend to be not full to the top. And sometimes if there is a small leak at a stave seam we’ll just pound the crap out of it with a 3 lb. cross peen hammer. That will compress the wood and usually force the seam together. These barrels are quite resilient. I’ve seen a new fill (weighing in at about 520 lbs) roll off the end of a four-foot dock, bounce a few times and not break open.

We hope you haven’t seen that very often. What’s the worst-case scenario?

If a barrel is lying in the rick and a leak forms on the bottom of the barrel, you’re going to have a bone-dry barrel of whiskey—possibly in a matter of minutes depending on the severity of the leak. That’s something we work very hard to avoid. But rickhouses are dark, there are a lot of barrels stacked up and we can’t be there all the time. We never like seeing a leak, but we’re always happy when we catch one. Honestly, these barrels are amazing feats of engineering and craftsmanship. Considering there are over 100 feet of sealing surfaces (and potential leak points) between all of the staves and head pieces, the precision required to make the beveled and curved sides of the staves straight enough and smooth enough to hold liquid, simply by pressing them together with steel hoops, is very high level.

What is your favorite part of the barrel aging process?

Next time you’re in a bourbon barrel warehouse, try to find a well-aged barrel with what looks like black goo leaking out between the head pieces. It forms when the whiskey is heating up in the summer and high pressure inside the barrel forces some of the whiskey out of a tiny gap very slowly. We call that barrel candy. It smells like maple syrup and caramel and all of the great aromas that make bourbon so tasty. But it tastes like the bottom of an ashtray. I get a lot of perverse joy out of getting somebody to smell it and then assure them that it tastes just like it smells. So, pick it off when you see it and hand it to your buddy. Tell him he hasn’t lived until he has had real bourbon barrel candy and watch his face as he “experiences” his first piece.