[1]

So, now we learn that corks do breath but just at first and not after a long while. I can go along with this explanation. If you examine the most recent permeability studies you will find, according to the graphs, that all closures allow some oxygen uptake. Whether it is from the time it takes for the closure to completely seal or that fact that there is more head space under the screw cap than the cork, or other mechanical difference, all closures release some air/O2 into the wine.



I don't find the reduction in SO2 such a mystery or hard to understand. The chemistry is relatively simple. SO2 is an unstable molecule. The stable form is SO3. SO2 is an oxygen scavenger. It takes up oxygen, changing from SO2 to SO3, thereby keeping the wine from oxidizing and also reducing measurable SO2. If we are careful and know how much dissolved oxygen our bottled wine has in it (easy enough to measure) we can add just enough SO2 to use up most of the O2 and not only leave the wine protected but not poison our customers with too much SO2. If the wine is clean and stable it will last a long time with very low or no SO2. SO2 is not a preservative at any rate.

[2]

Please tell me that I'm not the only one who understands the difference between Micro-Ox and Oxidization! More over the difference between aeration and the ever so slow influx of dissolved oxygenation into wine through the cork.



A cork is porous, absorbs moisture (ex. bottom of the cork in contact with wine swells) absorbs gasses, and can fail if allowed to dry out and shrink (your described instance of aeration and oxidization is an example of cork failure not success)!



For most wines – i.e. those lacking tannins and other antioxidant polyphenols – Micro-ox does nothing but deteriorate the antioxidant qualities of the limited S02 added, eventually leading to oxidized wine. However, for tannin and polyphenol rich wine (any age worthy wine in general) slow diffusion of oxygen in parts million over time helps to polymerize tannins. This happens at a faster rate when available SO2 levels decline.



On a recent visit to a winery in Michigan I spoke with the owner/vintner of some 30+ years. He was using a micro-ox system on some of his wines. He describes the process just as I have described. Duplicating what happens in a barrel which is exponentially faster than what we later see in a cork sealed bottle due to the difference in the surface to volume ratios of the wood sealing both vessels; the whole barrel is wood (greater O2 diffusion) and just the cork wood in the bottle (lesser O2 diffusion).



It is obvious that over time the development of ullage or headspace in both barrels and bottles proves that there is movement of at the very least liquid across the membranes of the so called "hermetically" sealed vessels. If liquid is moving through these membranes certainly gas is moving as well!



You need to accept that there is movement across the wood/cork barriers and then decide what is happening to the wine because of it. Certainly that last 1976 Chateau Montrose I had from my father's cellar last spring was not oxidized! I felt it still had significant cellar life to it! However the ullage was obvious vs. the 1996 Chateau Montrose we had side by side with the 1976! What replaced the liquid in the 1976 Montrose? Was it a vacuum? If so what effect would negative pressure have on your studies regarding the transmission (breathing) of O2 across the cork barrier? Did your study of decades ago take this into consideration!!!

[3]

A tremendously interesting article (I read the previous one also), but there seems to be something missing. I can't put my finger on it but I feel there's a lot more going on with this wondrous beverage than meets mine or the Dr.'s eye. One thing is for sure "Absolutes" have a tendency to become a little "Porous" with time.

[4]

Why would we age our wine in barrels if not for the micro oxygenation that occurs with oak versus stainless steel? If you say that the best way to age a wine is in an anaerobic state, then why expose any oxygen at all to it with barrels/micro oxygenation?

[5]

Peterson's latest diatribe is no more convincing than before, and the repeated use of the terms "absolute" (truth or untruth) and "idiot" still does nothing to strengthen his argument.

[6]

Sure, a champagne cork holds the pressure. But why does a wine that is freshly corked (without vacuum) in the bottle have the pressure equalize over a few days? Many plastic corks won't equalize and will push out. They supposedly don't have as airtight a seal between the cork and bottle. An oxygen molecule is smaller than a CO2 molecule and much less molecular weight. I also don't buy the interstices between the cork cells being so tight as to be impassable over time. We're talking a natural material here, not stainless steel. I still don't buy it, and much of Dr. Peterson’s quoted research is quite old and done with less advanced equipment that couldn't measure accurately. I agree much may have to do with the seal between the cork and the bottle, but I would think there is more to it than that.

[7]

On further thought I would like to suggest maybe a cork is like a depth filter (with a nominal and absolute rating). It’s tight enough to stop most oxygen molecules, but not all of them; but is tight enough to stop all CO2 molecules, which are just slightly larger. Just as a filter may be tight enough to block all yeast, but not tight enough to stop all bacteria, but will filter out most of them.

[8]

Ok Dick,

So what is your recommendation for closure? Are you arguing for Noma or Stelvin? Or do you still think that cork is a viable closure?

[9]

The AWRI did a study where they sealed wine in an ampoule. Such an ampoule is an absolute guarantee of zero oxygen transfer to the wine. I believe they also de-gassed the wine prior to filling so that it contained negligible oxygen. Many months later, they opened it and found SO2 had dropped significantly. The SO2 was only slightly higher than what was present with a tin-lined screw cap. This showed conclusively that there is some process that consumes SO2 in the absence of oxygen.

[10]

RE: [comment #2]…What replaced the liquid in the 1976 Montrose? Was it a vaccum?



Absolutely not. The liquid leaked out along the interface between the outside edge of the cork and the inside of the glass bottle. It happened after the cork got older because of the minuscule movement of the cork in and out just enough to allow wine to seep out and air to dissolve in the liquid and be sucked back in. A number of years ago we were worried about the use of lead capsules on wine bottles to dress up the bottle by covering the cork. We wondered whether it could be possible to contaminate the wine with a lead capsule outside the bottle. It was checked and, sure enough, a trace of lead actually got into wine (though the cork was unopened) over long storage.



There was corrosion under the lead capsule as a bit of lead dissolved in the tiny bit of wine that seeped out between the cork and the glass. When the cellar temperature dropped a degree or two the reduced pressure inside the bottle sucked the wine back in bringing traces of lead with it. That's the way your bottle got its ullage and it was certainly oxidized somewhat and had lost some bottle bouquet because of that. Bottles with significant ullage are never as well preserved as bottles of the same wine without ullage. Unfortunately all corks aren't identical. When I see a bottle in the cellar getting more than normal ullage, I use it up shortly after that because it is often still OK, though it wouldn't have lasted much longer. That should be normal procedure for any wine cellar, I believe.



I hope this helps.


~ Richard Grant Peterson

[11]

Dr. Peterson,

I read your article which I appreciated.


I have never told anyone that corks breathe though I have explained that the aging/maturation of wine is where many elements, chemicals and tannins are brought together bringing the wine to wholeness or completeness. A component in this process is micro oxidation which is exposure to oxygen through barrels, tanks, wine handling and in the bottle. Do you agree?


If not, please provide a better explanation of the aging of wine.


Thanks and I am looking forward to learning more!


Best Regards,

Jeff Landry

[12]

RE: [comment #11]…A component in this process is micro oxidation which is exposure to oxygen through barrels, tanks, wine handling and in the bottle. Do you agree?


Not with your last four words, because they aren't true. There is obviously a small amount of oxygen getting into wine as it is transferred between tanks, etc and into barrels. Once in a sealed barrel, the inherent reducing ability of wine removes all traces of oxygen, a vacuum develops inside the barrel and barrel aging is mostly anaerobic if the barrels are left sealed. The wine picks up more oxygen whenever the barrel is opened and during preparation for bottling. After the shock of bottling settles down as I explained, the cork no longer allows any O2 to enter. From then on, the wine is said to "bottle age" which takes place in the absence of oxygen so that the wine can develop bottle bouquet.


Once bottled (after that first month or so) if the cork leaks, the wine does not develop bottle bouquet; and that bottle of wine spoils within a year instead of aging properly. If the leak is large the wine probably becomes vinegar because acetobacter uses the oxygen to turn alcohol into acetic acid, which is vinegar. If the leak is very slight, the wine won't turn to vinegar but will just oxidize instead. It will lose its fruitiness and become darker within a year or two as the small amounts of oxygen leaking in destroy the flavor and color of the wine. The taste becomes similar to what I call "vegetable soup" and tasters recognize that the wine has become oxidized and ruined.


If you continue to believe that small amounts of oxygen can help a wine in the bottle, I have an easy test for you to do. Get two identical bottles of wine. White wines will show the effect easier but any wine will do it. Store them both in the same room temperature place. But open one completely, then replace the cork or screw cap in about five seconds (you can do this with either type of closure). Don't pour any wine out and don't let any air in (other than the small amount that will get into the headspace just by having the cap off for a short time). Wait a day or two, then remove the closure on that same bottle again, just for five seconds and reclose it. Wait another day or two and do it again every few days. You aren't adding very much air at all, yet the wine will already taste badly oxidized within a month (two at the most).


When you finally open the control sample to compare the bottles, you'll be amazed at how badly this trace of oxygen has spoiled the opened bottle. I tell you wine must remain without oxygen in the bottle to age well at all. If even a small amount enters, it spoils the wine, period. Even after a fine bottle of wine has aged properly so that bottle bouquet has developed beautifully, once opened so that air contacts the bouquet flavors, the bouquet won't last more than an hour or so, sometimes two. The wine is beautiful through dinner, but it won't last once air gets in. Bouquet is delicate and is destroyed by oxygen very quickly; there's no way it can develop in the bottle if traces of oxygen were to leak in.


The oxidation and ruining of wine can take place even before the wine is bottled if winemakers aren't careful to minimize the oxygen entry during handling and barrel aging. No winemaker leaves a part-full tank open to the air for good reason. The flavor loss just can't be recovered. In the bulk market, there are always wines for sale that are already oxidized and ruined. One sniff tells the potential buyer to save his money and just go away. The only thing you can do with wine like that is distill it to recover alcohol, but it won't be any good as a wine because oxygen is a primary enemy of the fruity flavors of wine. That's the reason a winemaker MUST keep twenty or thirty ppm of SO2 in the wine at all times during processing. Some oxygen can be tolerated during processing as long as there's enough SO2 to keep it minimized. But table wine just can't stand very much at any time. I hope you will try the test above. If you do you won't ever again tell people that micro oxidation is good for aging fine table wines.


Micro oxidation is only usable for wines that are to be consumed very young. It can make a "too young, new and fresh" wine taste like it's older – for a little while. All it really does is reduce the life of any wine it touches, to a greater or lesser degree. I suppose someone who likes a little oxidation might like a slightly oxidized wine but they won't like it next year. Micro oxidation insures that those wines won't last very long, even if they are OK for a few months.


I hope this is helpful.

~ Richard Grant Peterson

[13]

RE: [comment #4]…Why would we age our wine in barrels if not for the micro oxygenation that occurs with oak versus stainless steel? If you say that the best way to age a wine is in an anaerobic state, then why expose any oxygen at all to it with barrels/micro oxygenation?


You misunderstand. Barrel aging is most certainly different from bottle aging and they do different things. Of course wine gets deliberately oxidized a little during winery processing and barrel aging. Barrel aging gets rid of that "too fruity and immature" taste of very young wines and oxidation is certainly part of that. People like the maturation effect that it gives wine during barrel aging. Only after barrel aging happens to the degree that the winemaker wants is it time for bottling and the anaerobic phase (bottle aging) of wine aging. You have to remember that we are all different in our likes and dislikes, some like more barrel age, some less. Some like long bottle aging with bouquet development – but some prefer younger wines and don't like bouquet at all. It's OK not to like bouquet. I simply tell you that, if you do like it, you'll have to keep your bottles from leaking.


Personally, I still think natural bark corks remain the best closures we have for long term bottle aging, despite the occasional TCA catastrophe. But if I were going to bottle a wine for drinking in the next year or two, I'd be happy using a sound screw cap.


I hope this is helpful.

~ Richard Grant Peterson

[14]

Very interesting article. But what about barrel ageing? If barrel ageing is a more oxidative process than bottle ageing, which I believe is the conventional wisdom, will "Chateau X only bottle aged" last longer than "Chateau X two years barrel aged"? If not, why? I believe quite a few persons in the wine community will hold that barrel aged wines last longer, but are they in fact confusing a correlation to a cause (barrel ageing) with the cause itself (superior grapes)?

[15]

RE: [comment #9]…The AWRI did a study where they sealed wine in an ampoule. Such an ampoule is an absolute guarantee of zero oxygen transfer to the wine. I believe they also de-gassed the wine prior to filling so that it contained negligible oxygen. Many months later, they opened it and found SO2 had dropped significantly. The SO2 was only slightly higher than what was present with a tin-lined screw cap. This showed conclusively that there is some process that consumes SO2 in the absence of oxygen.



There are many such processes! SO2 is not so simple as you assume. SO2 combines readily (but loosely) with many carbonyl compounds in wine, which includes sugars, carbohydrates and oak components. In wine this combined SO2 is called "bound" as opposed to the "free" that has not yet been bound up by organic compounds. Bound SO2 acts like free SO2 in some reactions (but not others), so it can't be considered really "gone," even when it is partially bound up (partially neutralized) by the organic compounds.



SO2 analysis for wine includes both "Free" and "Total" because whatever SO2 is already bound can no longer help the wine stave off oxygen. It is the free that protects wine flavor from oxidation (by reducing oxygen) and, as a practical matter, it is only the free that we pay attention to in assessing oxygen entry, not the bound. To complicate matters, under its own set of conditions some of the bound SO2 can be oxidized as well as the free. Bound SO2, just like free SO2, gets oxidized by Iodine in the analytical method to detect it, for example. To make the study really worse, we think of SO2 as a reducing agent but it sometimes acts as an oxidizing agent as well! We know that both free and bound disappear from wine during long aging in sealed containers. They appear to get combined into some of the complex compounds ending up as polymers and brown pigments in very old wine. See "Chemistry of Sulphur Dioxide in Foods" by B. L. Wedzicha, Elsevier Applied Science Publishers, London & New York (1984).



The paper you refer to did more to measure the effectiveness of the tin-lined screw cap to exclude oxygen than it did to elucidate the combining of SO2 by wine components. I hope this is helpful even though I fear it is more chemistry than most people care about.


~ Richard Grant Peterson

[16]

It is still not clear to me which reactions are responsible for the aging if it is not a reaction with oxygen. I thought tannins, like SO2, were an antioxidant, and that a reaction with oxygen breaks down the tannins and produces new molecules which improve the bouquet. If this is not the case, where did the tannins go?



Also, a wine that would need cellaring but which is opened too soon (too young) improves when given air for a few hours. The tannins soften and the bouquet develops. The same wine that is properly aged (but not old) does not benefit as much from this treatment and can be drunk right away. If this is because of aeration, and not oxidation, as you suggest, how come that the younger wine (which is less reduced and would therefore need less air) benefits more from this treatment than the older wine?



I agree with your statement about letting old wines breath a bit, but it seems to me something different is happening when you let a young tannic wine breath for 24 hours. The development more or less resembles what happens during a few years of aging in the bottle. Is this just a coincidence?

[17]

If cork is preferable for closure, and most leakage occurs at the glass-cork interface, what about using Sealing Wax to obstruct any leakage that may occur there? Have there been any studies to test the effectiveness of Sealing Wax?

[18]

I really enjoyed your article and did learn a few things. I have never associated temperature change with cork movement and thus seepage. I always thought that temperature had more of an effect on chemistry. Thanks for that enlightenment. I have been making wine for 28 years (following the footsteps of my father and grandfather). Given the facts you have stated, is there any good reason to lay bottles down? I thought that the corks had to be kept wet to keep a good seal. From what you have stated it seems the wine lubricates the cork making seepage and potential inbound movement of air increase over time. If air can't get through the cork (from outside to inside the bottle) then why not leave the bottle upright?
Looking forward to your reply.
Cheers,
Owen Taylor

[19]

Great info, I sucked it up. Hmm, I must have been breathing in. I write about wine and do presentations, classes on same, so this was invaluable and well written. Thank you!