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08.12.2009

Wine Geek Out: What They Know About Oxygen and Wine

oxygen.jpgForgive the pocket protector with the waiter's friend protruding from it: I'm a wine geek at heart and sometimes I can't help myself. If you would rather just drink good wine without thinking at all about how it is made, close your browser right now, because things are about to get geeky, thanks to a great article by my fellow blogger and wine science buff Jamie Goode.

We still don't know a lot of things about wine. It's a complex animal, where a lot of variables are in play, and direct cause and effect relationships are often difficult to pin down. For instance, we remain mostly in the dark about the relationship between the mineral content in the soil and specific flavor components in the wine. We know there is a relationship, but we have a very hard time linking specific flavor compounds to specific aspects of geology, despite a clear sense that some link must exist.

Likewise, we are only just now beginning to understand the specifics of how wine interacts with the tiny little bit of oxygen that bounces around in the neck of the bottle between the liquid and the cork or other closure. Even more befuddling, until recently we've been mostly at a loss to definitively say how much oxygen gets into a bottle as it ages through various closures.

For those like me to whom such unanswered questions are annoying mysteries, thankfully there are a lot of folks much smarter and well equipped than us who spend a lot of time trying to actually find the answers.

In a recent article in Wines & Vines magazine, Jamie Goode lays out the current state of our understanding of how oxygen plays a role in wines evolution, and in particular, what we now know about how much oxygen gets into a wine through corks, screwcaps, and other closures, and the impact of this transmission.

Goode reports on a very large collaborative study being done by a number of closure companies research institutions, lead by closure manufacturer Nomacorc. While it is undoubtedly self serving in some respects, it appears to be rigorous and unusually collaborative science that already is yielding some great insights into this murky corner of wine science.

The variations in oxygen levels in wine as a result of bottling vary considerably, from .6 parts per million using a vacuum sealed bottling line with screwcaps to 4.4 parts per million with a wine bottled purely by hand. While it may sound obvious, it was not particularly well established that this amount of oxygen plays a significant role in how the wine ages, in addition to the added factors of how much oxygen enters through the closure.

The oxygen in the "headspace" (the area between the liquid and the bottom of the closure, ends up being absorbed by the wine in about 10 months of aging. And once in the wine, that dissolved oxygen goes about doing a lot of things that basically involve "aging" the wine. In particular, affecting its color.

Interestingly, a number of tests were done on different bottling lines that showed the amount of oxygen in each bottle was remarkably inconsistent, and that the amounts by which the oxygen levels varied were significant enough to likely result in differences in how the wines would evolve. The implication being that this may be a large factor in the well known phenomenon of "bottle variation," which anyone used to frequently consuming older wines will have encountered.

I won't go on to repeat all the findings or background that Goode includes in his article. Go read it yourself.

We now return you to your slightly less geeky normal programming.

Image courtesy of mag3737 via Flickr.

Comments (23)

08.13.09 at 12:06 AM

Thanks for drawing our attention to this, Alder. It's always good to get news of one of my wine writing colleagues in London via San Francisco. A very useful article. And how delightful that the stopperers are co-operating at last. Down with murkiness!

08.13.09 at 1:39 AM

I once read something on this issue in an article that was debating about cork vs screw caps and it mentioned that the aging of wine in the bottle is mostly anaerobic. Then i saw mentioned in another place that you shouldn't decant Brunello wines because the contact with oxygen that they receive once in the glass is enough to open up the wine and sort of "commit" these changes that happened while the wine was sealed.

08.13.09 at 2:04 AM

Wrote too soon. Closer examination of the article reveals no co-operation between different closure manufacturers as far as I can see, but a useful research program sponsored by Nomacorc, makers of synthetic corks. Should have known...

Kevin Cohen wrote:
08.13.09 at 6:32 AM

Alder- Thank you for the information...very interesting. I read an article a few months ago that talked about when wine is exposed to oxygen, chemical communication occurs. I thought that was an interesting way to putting it.
Salute!
-Kevin

Alder wrote:
08.13.09 at 7:31 AM

Er, my bad. The collaboration is between several research institutions, not closure manufacturers.

Vivek Bellore wrote:
08.13.09 at 7:49 AM

This is one subject that I think gets too little attention, so keep them coming.

It seems that the "science of wine" might be the type subject best evaluated by crowd sourcing? I wonder if there are simple home made tools that can be used to measure different variables within wine. Average storage temperature seems to be an easy one, maybe there are others, like pH tests . . .

It would be interesting to see a winery seize this topic and encourage their mailing list to share as much data as possible about the conditions under which their wine is stored, opened and consumed, as well as the immediate chemical properties of the wine.

Dylan wrote:
08.13.09 at 7:54 AM

This information goes along with things I've been learning during fermentation. Due to Angel's Share and samplings, the barrels will become less full of wine and more full of oxygen. As this happens, there's a constant balancing act involved in reducing the amount of air to the proper level. Still--I never considered that such a tiny fraction of air in bottle would commit this kind of variation.

Jim Gordon wrote:
08.13.09 at 9:17 AM

Jamie's article fascinated me partly because it seems to settle an old argument about whether bottled wine ages through reduction or oxidation. As I recall the enology profs said it was reduction because the cork did not allow oxygen transfer and the head space oxygen was insignificant. Traditionalists including Lalou Bize Leroy, then of Domaine de la Romanee-Conti argued back in Wine Spectator that of course there was oxygen transfer around the cork. Looks like she was right.

Arthur wrote:
08.13.09 at 12:42 PM

I seem to recall a piece on Appellation America a year ago or so that asserted the same thing: the oxygen comes from the ullage as well as from the cells in the cork.

Alder wrote:
08.13.09 at 10:14 PM

Vivek,

Thanks for the comments. What an interesting idea you have there. Sort of like the SETI@Home project, if everyone put probes in their wine, we'd get a ton of data. At some point I'm sure that will not be prohibitively expensive. Some of the top wineries already embed RFID chips in each bottle.

Alder wrote:
08.13.09 at 10:18 PM

Lorenzo,

I've read a lot of conflicting stuff over the years about oxygen and wine aging, so it's nice to see some fairly definitive science on it. I ALWAYS try to decant Sangiovese, and Brunello in particular as far in advance as possible. More so than any other grape, Sangiovese really seems to require a lot of oxygen contact to open up. The younger the wine, the more I decant, but even 20 year old Sangiovese regularly sees the decanter for at least an hour prior to drinking in my house.

apj powers wrote:
08.13.09 at 11:24 PM

Interesting topic.
I am reading a book to prepare for my internship.
It is by David Bird. He is a Chartered Chemist AND a Master of Wine.
And he tries to explain things in a more conversational tone.
The book is 'Understand Wine Technology, The Science of Wine Explained' (and NO, this isn't David). A must read for sommeliers & students of wine. IMHO
It is great if you want to know more, but you do not want a Chemistry degree. --AP

Robert wrote:
08.14.09 at 10:52 AM

Please stop referring to yourself as a "wine geek" and "geeking out" on wines. This is just about as annoying as when political writers talk about how "wonkish" their opinions are.
YOU'RE NOT WRITING ABOUT ANYTHING THAT COMPLICATED. REALLY.
This just comes off as a lame way to make your readers feel special for following your posts.

Alder wrote:
08.14.09 at 11:53 AM

Bob,

Thanks for taking the time to comment. But I'm a little mystified as to why you're having what appears to be a strong reaction to a pretty common term in the wine world that is most often used with affection.

From Merriam Webster: Geek: an enthusiast or expert especially in a technological field or activity.

Most of the time when I write about wine, I write about the people, places, and stories behind the wine. That's what I love the most, and what I think most people relate to the best.

But I also have a fascination with the science behind it. MANY people do not. In fact, deconstructing the winemaking process even to its basic high-level chemistry is a sure fire way to bore many readers to tears.

I think many of my readers could care less about dissolved oxygen levels in their wines. They just want to enjoy good wines without thinking too much about it.

So before I launched into this article that I know wouldn't appeal to everyone, I described the coming conversation as geeky to both characterize it as different from my normal focus, as well as to acknowledge that for some of my readers, this sort of discussion isn't to their taste, and to allow them to skip it if they like.

Call that lame if you like, but it's not an effort to make anyone feel special. Instead it's designed to make people feel comfortable, myself included: To make me feel comfortable writing about something that I know many of my readers don't care about. To make my readers comfortable with the knowledge that I know that, and won't be turning Vinography into TheScienceOfWine.Com.

Colman Stephenson wrote:
08.14.09 at 4:11 PM

Jamie Goode does a terrific job of rigorous scientific coverage and BS-calling while avoiding reducing the human and mysterious aspects of wine-making to mere facts and figures.

apj powers wrote:
08.16.09 at 6:32 PM

Alder: I agree with your reply about the use of the term "geek"
I figured out that sometimes when I approach a table (as the sommelier), the host only wants someone who will listen to his winespeak - his guests having grown weary of it long ago. I offer a little of my time and attention. Often, the host never even asks for a wine suggestion. Lots of people tune out on geeky wine talk quickly...zzzzzz

John Kelly wrote:
08.17.09 at 12:10 AM

I guess now I know how a politician who is deeply versed in the minutiae of policy on a particular subject must feel when confronted by the average "low-information" voter. Or maybe I just feel like Napoleon Dynamite reacting to Uncle Rico. Either way - ouch.

So here's the deal: First, the hundreds of chemical oxidation-reduction couples that are at any moment moving towards some local minimum in the equilibrium plane during wine aging are only fractionally dependent on the presence of molecular oxygen. The saturation level of oxygen in wine at normal temperatures is around 8 ppm, while things that can react with oxygen like SO2 at bottling might be 25 ppm and phenolics might be 200-2500 ppm - orders of magnitude greater than the level of reactive oxygen. Parts per million is a stupid measure, but even correcting to molar values (or better yet, molal values) for the different chemical species involved, species that can "absorb" the oxygen that may be present are WAY in excess of the oxygen present at bottling. Oh, and BTW - that two milliliters of ullage between the wine and the cork? It's less than 20% oxygen.

Second - most of the extractables from natural bark corks are phenolics, which are capable of reacting with oxygen. Synthetic stoppers have none of these extractables. Bark corks actually contribute things to the wine that can positively benefit development in the bottle, and inhibit "oxidation."

Third - whether they come from bat-blind "researchers" or self-serving stopper producers, studies that focus on how much oxygen a particular closure allows into the bottle miss the boat completely. Yes, the type of closure makes a difference. But the finish in the neck of the bottle makes an even bigger difference. I suggest that if glass makers could produce bottles where the inside of the neck is round, smooth and parallel, to the kind of tolernaces demanded by the mating surface for a screw cap, bark corks and synthetic stoppers would be as impermeable to oxygen as screw caps. Actual production wine bottles? not so much - THERE'S your "bottle variation."

I could go on and on, but I've geeked out enough and I'm bored with this topic.

Alder wrote:
08.17.09 at 8:38 AM

John,

Thanks for the comments. At the moment, your comment comes off as quite pedantic. As if you're competing in a "who can use bigger words" competition, where the sole goal is to trash the competition. Do you mind translating into English for the rest of us and laying out some implications of what you're saying? Sounds like you know your stuff and it would be great to learn something from you.

keegs wrote:
08.17.09 at 9:00 AM

I speak Jive, I think I can translate (with apologies to John). The amount of Oxygen dissolved in the wine and in the ullage is really small in comparison to all of the amount of molecules that could/would react with it so is of little or no import. Bark Corks also have substances that can react with the Oxygen and may actually do good things to the wine (I had not heard of this) And while the type of stopper may make a difference in the wine, bottle variation may actually come from the bottle. This is caused by problems due to lack of tolerances in bottle production.

Colman Stephenson wrote:
08.17.09 at 9:37 AM

Thanks John Kelly. Interesting stuff.

Now it would be terrific to have the sources for the evidence that the cork contributes other substances and that variations in the surface of the glass in the neck may cause bottle variation.

Further reading please.

As for point three (oxygen transmission is more to do with the glass then the cork), clearly any Oxygen transmission is a result of the combination of the bottle and the stopper (whatever the materials). So as long as the glass is inconsistent (and we need evidence for that) then debate around the nature of the cork or other closure doesn't amount to 'missing the boat'.

John Kelly wrote:
08.17.09 at 9:43 AM

Hey Alder:

Pedantic? Yeah I taught Clark Smith to suck eggs. Your post was good. Thanks for the heads-up on an important topic. And thanks to keegs for translating my post :-)

John Kelly wrote:
08.17.09 at 10:29 AM

Colman - really? "Cite your sources"? :-)

I've been making wine professionally for 23 years but have yet to see a paper in AJEV or anywhere else quantifying cork extractables. But it's kind of self-evident, isn't it?

My observation on the finish on bottle necks is also sort of bleeding-edge. Check the specs from the manufacturers. They only guarantee that the inside of the neck is sort of round and straight for the first 15mm or so from the top of the bottle - about 1/3 the insertion depth for most closures.

Chris Lopez wrote:
08.21.09 at 2:54 PM

Sorry for posting so late, but I love the wine-geekiness! I have been reading "The Science of Wine" lately (at your recommendation - thank you!) and this article ties in well with parts of the book.

More Geekiness Please!

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