Feature Article
  Sign In
Subscribe to our newsletter
Bookmark and Share  
print this article    

Feature Article

Corks do not breath.

There is solid scientific evidence which demonstrates that corks are perfect enclosures for wine,
discounting TCA of course.

America (Country Appellation)

Please Stop Telling People
That Corks ‘Breathe’

Who would have thought that wine corks would be so controversial. The voluminous reader response to our features on the pros and cons of corking wine continues long after the articles have appeared. Our learned guest columnist, Richard Grant Peterson offers some empirical evidence to prove that corks have been used for ages because...they work.

by Richard Grant Peterson, PhD
February 10, 2008

Editor’s note: The following article contains the opinions of Dr. Richard Peterson. APPELLATION AMERICA has published them in the interest of continuing the dialogue on the cork controversy and particularly the debate surrounding our previous article on NomaCorc cork research. Dr. Peterson’s expressed thoughts should not be interpreted as representing those of APPELLATION AMERICA.

DropCap Sad to say, most articles about the pros and cons of using corks for closing wine bottles end up parroting at least one absolute untruth. Contrary to anything mystic that you may have heard, I can tell you categorically that sound corks do not breathe air.

I have published a simple statement to this effect many times over the years, hoping it would be memorized by all, but alas, here it is one more time:
“Show me a cork that breathes and I’ll show you a bottle of vinegar.”
“Show me a cork that breathes and I’ll show you a bottle of vinegar.” I believe I first published that in the early 1960s and it has stood the test of time scientifically. But it seems not to have withstood the unending human quest to keep regurgitating old wives’ tales into the untrue lore of wine.

I agree that it sounds glamorous to say, "closures 'breathe' at some mysterious rate which controls the process of bottle-aging precisely" (as if any winemaker ever knows exactly when each bottle of wine will be opened and can time the "aging" to match the consumer's whim). The problem I have with this old fable about corks breathing is that it’s pure B.S. It’s high time we stop seeing it reprinted.

We did the lab work almost five decades ago! It’s been repeated more than once in Australia and all those who’ve checked this in the lab tell the same story: Sound corks do not transmit oxygen! Even more important, neither is oxygen transmission through closures what we want! Wine aging and the development of 'bottle bouquet' during bottle age is anaerobic, never aerobic. The effect of continued aeration of wine in bottle is something quite different, and antagonistic to the development of bottle bouquet. Aeration of wine by a leaking closure does at least three things, in steps:

(1) It oxidizes and removes the SO2 protection from the wine, then;
(2) It oxidizes and removes the tannin, pigment and other polyphenolic protections from the wine;
(3) It oxidizes and destroys the flavor of the wine, followed closely by browning, polymerization of the oxidized pigment and other polyphenols, etc. cork-nose-200.jpgThis completes the oxidative destruction of what would have been a perfectly preserved bottle of fine wine if the closure hadn't leaked air into the bottle.
(4) Separate from the above oxidation reactions, air, in the presence of certain bacteria, (which wine always has), allows them to grow in the wine and turn it from wine into vinegar.

I’d like to take the space here to answer one of the most prevalent questions I hear from the wine drinking public. There is a great deal of confusion about the 'good aeration' of decanting before drinking an old bottle of wine - and the 'bad aeration' that can lead to oxidation. Most people don't understand either one of them, but neither is very difficult.

First, you need to recognize something that most people have never thought about: Everything we eat or drink is bathed in air as it passes over our taste (& nose) receptors. We are used to whatever the taste of air in food and drink is. We like it. But old wine is not like most foods that we eat or drink, at least not when the bottle is first opened. Old wine has been sealed up inside a bottle for many years and something changes during that time. The wine is no longer ‘bathed in air’ and it will taste funny at first, until we bathe it in air before drinking. We live in a world of chemistry and that is sometimes confusing. You see, old wine has been living in a ‘reducing atmosphere’ in the sealed bottle, which is the chemical opposite of aeration (an aerated atmosphere).

Do not misunderstand: Aeration is not the same as oxidation.

cork-stack-225.jpgWhen you aerate an old wine, you mix air into it and that makes it easy to drink and enjoy. Trust this for a minute and it will become clear. Freshly dissolved air doesn't oxidize the wine immediately - it cannot, until it has had time to do so. The oxidation of wine by dissolved oxygen takes place slowly and you won't see the effect for several hours after aerating, maybe even overnight.

Once a wine has become oxidized, it is dead and cannot be revived because the oxygen has attacked flavor and other components of the wine and changed them into something other than wine flavor. Think of an aerated wine as simply mixed with air, where the air hasn’t had time enough to attack and oxidize the wine as yet. Your job is to drink the wine while it is aerated but well before it could get oxidized.

In graduate school wine research, one of the enduring chemical truths I learned from a genuine master, Professor Maynard A. Joslyn, was that "Wine in a closed container quickly becomes ‘reducing’ on its own (accept this chemical term for the moment), and wine lives naturally in a ‘reducing atmosphere’ in sealed barrels, tanks or bottles." That is extremely important to know if you want to understand bottle aging.

I've opened many bottles of 30+ year old Cabernet wine and, nearly always, those wines have a 'reducing funk' at the time they are first opened. There is no H2S - they aren't "reduced" in that sense, but only living in a ‘mildly reducing’ atmosphere. They just don’t smell right at first. All they need is to be decanted to remove solids, if present, and then aerated by being poured, with splashing, back into the (rinsed) original bottle. Then allow the wine to stand in its now aerated state for another few minutes before serving.

The reducing funk disappears for good reason: We are used to whatever the taste of air in food and drink is. We like it and we want to drink our wine mixed with air, same as any other food or drink. Since old wine has been sealed up inside a bottle for thirty years in a ‘reducing atmosphere’ - the chemical opposite of aeration - we have to get it into an aerated atmosphere before drinking. All we have to do to bring out the goodness of the wine’s aroma and bouquet is aerate a little to re-establish the aerated surroundings we want to taste it in and, presto, decanting does the trick.

I tell you this so that even non-chemists will understand the truth that wine aging never takes place under aerated conditions. It's because those are the conditions that will lead only to oxidation in time, and destruction of the good things in wine. In a perfectly sealed bottle, the wine will not oxidize but will develop bottle bouquet - which it cannot do if that #%$&@! destructive oxygen is present.

basic-cork-125.jpgOkay, I’m a realist. I know that some people are going to continue defining "wine aging" as 'slowly oxidizing it until the wine isn't drinkable any more', if they want to. That's what those idiots do when they promote deliberate oxidation of your wine through selectively defective closures, although I don't think they do it on purpose - it's just that they lack chemical common sense.

Featured Wines

Jewell Towne Vineyards Cabernet Sauvignon A full bodied red with hints of red currant, black fruit, and toasted oak.
buy wine 750ml $14.00

Wollersheim Winery River Gold
buy wine 750ml $7.00


Reader Feedback

Reader Comments... [44]

Arthur Przebinda , Founder
redwinebuzz.com, CA
Dr. Peterson, I share your passion for the scientific basis of wine making and all things relevant. With the understanding that free O2 is not necessary for RedOx reactions to occur, I have always thought of a properly sealed bottle of wine as existing in a state of equilibrium leaning towards a reductive balance because of a lack of reagents. I do need some clarification from you to understand the matter better: Show me a cork that breathes and I’ll show you a bottle of vinegar.

You say all wine has bacteria (presumably Acetobacter?).
– What about the use of sterile filtration in modern wine making?
– Additionally, does Acetobacter thrive in a solution which is 13% ethanol (or more)? Is there a concentration of ethanol that is bacteriostatic or even bacteriocidal to Acetobacter?

I would like to hear your thoughts on this matter as the wine turns to vinegar notion is typically thought of as a wine myth.

James Forchini , Owner/Winemaker
Forchini Winery, Healdsburg, CA
Thank You, doctor Richardson, for your article -- corks do not breath. I have held this position for the same reasons you state for many years. I believe the slow oxidation of phenolics and other compounds in the bottle comes from the absorbed O2 in the wine, not through the cork. I also believe - w/o proof - a cork becomes a time capsule for the slow release of O2. The O2 becomes trapped in the inhomogeneous pores of the cork after compressing for insertion in the bottle. With time this O2 transfers to the wine as a result of the negative pressure in the bottle and other Oxy/Red forces. I also package and store all our wine neck up to minimize TCA contamination and have had a TCA incidence of < .5%, whereas industry ranges seem to be 3-7% for neck down. I have lost sales brokers and customers for my belief. I’ve been called a maverick, but I feel strongly about this and continue to do what I feel right. Our 3000 case winery’s sales increase each year.

Tom Hedges , owner
Hedges Family Estate, Red Mountain, WA
You do not use the word ullage, which is air space between the wine and bottom of the cork. I do remember from chemistry that matter can neither be created nor destroyed, so where does it go when ullage volume increases over time? It happens with barrels, too. Even if the wine vaporizes, it still left the liquid state and went somewhere. Is it all contained inside the cork, or in the case of oak barrels, impregnated in the wood? Doesn’t air replace this wine, or is it a perfect vacuum?

Keith Pritchard , Owner
Slate Run Vineyard, Ohio
I have read numerous articles about permeation studies and having it at the right rate so as to age the wine properly. Screw caps generally have been either too tight or have too much permeation. Synthetics are too tight to begin with and then let too much air in later. Here is a link where they mention a permeation study. I really just do not buy your take on it. I have read about a great number of these types of studies. Maybe your research was done with old equipment a long time ago and is out of date.

Gordon Rawson , Winemaker
Chatter Creek Winery, Woodinville, WA
Thank you Richard!
Please now please explain how SO2 does not protect wine from oxygen but merely masks it by binding up the aldehydes caused by oxidation until it is exhausted and then goes to work on steps 2, 3, and 4, and I’ll gladly post it in my tasting room next to my wines finished with screw caps.

Bob Hodgson
Thanks for the education.

Gideon Beinstock , brain-scorched red neck
Clos Saron, Yuba County, CA
The content of this article apart, I found I had to repeatedly keep myself emotionally neutral in order to remain receptive to its message. I found the tone of the writing negative, defensive, aggressive -- why? I do not know the writer and do not really know the reason. Could it perhaps it be related to the historical fact that, as we all know, a lot of so called scientific truths sooner or later are blown out of the water by newer, better, other "scientific absolutes". By the way, I tend agree with most of the article content, although wine -- including its aging -- still mystifies me. Well, yes, I know that scientists tend to be irritated by this human weakness of being 'mystified' by something...

Kareem Massoud , Winemaker
Paumanok Vineyards, North Fork of Long Island, NY
This is a great article. Thank You, Dr. Peterson.
The logical question if you understand this article is: why should I keep using cork if there are other closures that provide an equally tight or tighter seal and that won’t contaminate my wine with TCA? It is precisely for this reason that we have just bottled Long Island’s first wines sealed with a screw cap! It has been demonstrated that a typical stelvin type closure forms a seal as tight or tighter than a top grade 2 1/4 inch cork. There is a big misconception (to which I plead guilty to having believed myself) about a wine’s potential to become reductive and for that potential to be exacerbated by screw caps, due to the tightness of their seal, and for it to result in serious sulfide issues in the wine. The reality is that if the wine is bottled with any residual sulfides, or if it has the potential to become reductive and form those sulfides in the bottle, it will do so regardless of the closure. From a wine quality point of view, I can not see any reason to keep using cork.

Lise Ciolino , Owner / Winemaker
Montemaggiore, Healdsburg, CA
Dr. Peterson:
Please provide references to recent scientific studies to substantiate your beliefs. Given many contradictory claims, readers appreciate being given tools to further investigate the issue and decide for themselves.

Thank you for your article regarding breathing corks fable. Then does it matter the type of closure that is used as long as it seals properly and will not negatively add a flavor to the wine, i.e.: a composite cork, a cork made of alternate materials, a screw type?

To post your comments on this story,
click here

Most Popular