Ask Wine Wizard

Oak Barrel Seepage


Eric Weinstein — Maine asks,

I recently purchased a new 32-gallon (121-L) wine barrel made of Hungarian oak from the Zemplen forest. I should let you know that I have been making wine, one of which won a Silver Medal in the WineMaker Amateur Wine Competition, for over 30 years. I have used French and American Oak before but this is the first time for Hungarian. I treated the barrel properly as per instruction, and then put my wine in it. To my surprise, the wine started to seep, not from between the staves or the barrel heads but through the staves themselves. The seepage was fairly wide spread affecting about half of the belly. I was told that wood from the Zemplen forest was so dense that in fact you need to keep wine in barrel for 14 months or so. I seem to have halted the seepage by using wax but now I am wondering about the state of my wine. Is there anything I should be worried about or any additional measures I should take to protect the wine? Have you heard of this happening before?


I’ve certainly had the odd leaker (or three) but I’ve never experienced trans-stave leakage of the scale that you describe. Before I delve any deeper, I first of all would like to say that your situation is unusual and one that warrants an immediate customer service call (read: complaint) to your barrel supplier. It is normal for barrels to need a little soaking up with water before they can be filled with wine. Sometimes we even need to go beyond the “instructions” and use hot water on the barrel head or something like that to properly swell up a barrel. Your type and scale of leakage, however, goes far beyond what is normal and in fact travels headlong into “product defect” category. Any self-respecting barrel supplier should show you the proper concern and offer to exchange your product.

Let me describe why I believe your situation goes quite beyond the expected “new barrel” seeps and leaks most of us are used to. Oak barrels (and barrels made of other woods, sometimes acacia wood or even cherry wood) are really structurally amazing. I liken a well-built barrel to a lovely piece of furniture. Just like a well-built chest of drawers with hand-cut dovetail joints, a correctly-made barrel is an exercise in close-fitting wood pieces held together by pressure and a little hardware (the metal hoops, to a cabinet’s finishing nails). The species of oak used in France, Hungary and the US for cooperage are all nice and hard (they can hold water) but are still also “soft” enough to be bent with heat and steam as they are in barrel making. As we all know, wood is a natural product and can lose moisture over time, drying up and shrinking. This is why introducing steam or water into the barrel is often necessary (“swelling up the wood”) before a new barrel is ready to store wine. It’s also just smart to rinse water around in your new barrel to check it for leaks, just to make sure you know what to expect.

A barrel is made up of exactly-cut staves (the long wood pieces) and two round barrel heads held together by the pressure exerted on them by the hoops, which are gently pounded on to hold all the pieces together. The stavewood in turn is cut from sections of a tree. Oak trees have almost-microscopic tubes called xylem and phloem running vertically up and down them. These tubes are essentially the tree’s veins, and carry the tree’s lifeblood (carbohydrates, minerals, water, etc) to all parts of the plants. When a tree grows straight up and down, these little tubes run straight up and down too. When a stave is shaped from a straight tree, the tubes generally run lengthwise up and down the stave as well. If you look closely, you can see evidence of this “grain” and tubular material at the end of each stave by the barrel head. Straight-growing trees are best for barrel-making because the little tubes, for the most part, run along the whole length of the stave, parallel to the wine inside, not presenting many open channels through which wine can travel through the stave to the surface. This way, the only leak points are the small spaces between the staves themselves, not within the wood of each stave. These between-stave leak points are what we normally swell up when we “soak up” a barrel.

If, however, an oak tree grows crooked, the little tubes grow crooked too, and a stave cut from a crooked tree will have the little tubes going all over the place, undulating back and forth through the “straight” stave that has been cut from the crooked wood. This means that there is a greater chance of ends of these tubes being shaved off and exposed on the outside (and inside) surface of the stave as it is cut and shaped. Now there exist channels through which wine can migrate after filling, from whence come horror stories like yours where the staves themselves are leaking wine through them. Most barrels will have some “open” xylem or phloem because the staves are always planed towards the end as the chime (the end of each stave where it attaches to the barrel head) is shaped. In properly made barrels, these few holes will close up easily with the “soak up” we’ve discussed. However, in a bad case like yours, a fatally high number of trans-stave channels are present and the entire barrel’s integrity is compromised. In short, you’ve just put your wine into a leaky sieve. (It’s either that or you have a well-hidden internal crack that goes across a few staves, which could be caused by a dropped barrel, but I believe it’s the former.)

What to do? Get your wine out of the barrel as soon as you can and get your barrel supplier on the horn. I’ve had to get pretty aggressive on barrel-soaking once or twice over the years. With small barrels like yours, I’ve sometimes had to completely submerge them in a half-ton picking bin or plastic garbage can full of water and leave them there for 48 hours to get the kind of soak I needed. Sometimes I’ll have a little wine seepage that corrects itself after 12 hours or so. If, however, after 48 hours of complete soaking I still have a big leak (and not a teeny seep), that barrel has a problem and your supplier needs to do something about it. Here in Napa, if I have an issue, my cooper will make “cellar calls” and sometimes will help me plug up a little leak with some paraffin, or may even refit a head if need be. However, I can tell you, that my salespeople would never let me suffer through as much trans-stave leakage as you are describing. Bad wood makes bad barrels and bad barrels make bad wine. Barrels cost a lot of money. Don’t put up with it.