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natbouman

Oak is not permeable to oxygen

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I recently read a new study published in Vine and Wine Open Access Journal . Here's the URL:
 
The authors studied the transfer of oxygen through oak and between oak staves in a barrel. They found that whether the oak is wet or dry, there is no--or nearly no--oxygen transfer across the oak . Here is a quote, "

"At the end of the measurement period, the dissolved oxygen level is lower than 0.5 mg.L-1. We can consider that oxygen transfer through imbibed oak wood is seriously limited because no oxygen transgresses through this porous material after 45 days."

The study goes on to claim that oxygen passes through to the liquid from desorption (the oxygen which is already in the wood itself, but not from the outside of the barrel, leaches in) and oxygen passes between the staves--particularly where the staves are contacting with less pressure (nearer the bilge). Desorption accounts for a previously observed spike in oxygen in the first weeks of aging.

I was pretty surprised by this study as I've always heard that the oak itself is permeable to oxygen. Instead, it seems like it's the barrel construction more than the wood which impacts oxygenation. This is a french study, so they used french oak--but I kind of doubt american oak would be substantially different.

This study looks pretty legit to me. I read through their methods and I was fairly convinced--though I'm no scientist. I was curious if anyone else found this study convincing.

It made me wonder about the claims of barrel alternatives like the "squarrel." If this study is correct, some kind of stave gap would be necessary if you are seeking oxygenation of your spirit.

 

 

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A couple thoughts, after a brief skimming...

a) After 45 days they saw 500 ppb worth of DO, which is low, but also not 0. 45 days is a very short period of time, and in the paper they stated 9 months was half the O2 as a year, so these numbers seem to increase greater than linearly (I won't say exponentially).

b) French oak and American oak are cut differently for barrel manufacturing, I am guessing as a result, American oak is slightly more porous. (Just a guess)

c) The oak itself may not be very porous, but barrels are, I conducted a scientific experiment yesterday by walking into a barrel room and I smelled whiskey.

Papers like this are interesting, but I always struggle with what I am supposed to take away from it. I'm not going to stop aging brandy and whiskey in oak barrels any time soon. Nor am I going to start doing micro-ox on finished spirits.

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I believe that French oak staves must be made by splitting instead of cutting because French oak is more porous. Splitting allows the wood to break on natural fault lines that result in closed pores. French oak is less dense and contains less tyloses.

Does this study mean one should stop using barrels? Clearly no. I think it does help me evaluate the claims of barrel alternatives. Also I’d be curious about the interstave pressure of small barrels. Does it approximate larger barrels—and thus mimics larger barrel o2 transmission or are there substantial differences?

Can I slightly loosen hoops to increase o2 intake?

idk, maybe it’s not useful info but I like understanding the process better even if I don’t know how to manipulate it practically, yet.

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French oak (both species) is looser grained and more porous than American oak. 

I also don't really grasp the relevance of this information. I imagine loosening the hoops would cause leakage and seepage, and using a clothed bung (or just removing the bung periodically, like to sample it...) would introduce more oxygen. 

 

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I'm not exactly sure what the impact of the information would be. Perhaps nothing. It does seem relevant though. At any rate, I just think it's interesting. I mean, oxygenation is a fundamental part of aging right? So, perhaps the mechanism by which the oxygen enters the spirit is different from what has been assumed for ages. How might this information be used? IDK. Perhaps someone who is interested in more rapid oxygenation would be interested in a barrel made with more and narrower staves. Or yes, someone could just remove the bung with greater frequency. Maybe I'll start doing that.

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