Wine Talk

Snooth User: Charles Emilio

How can a wine 'age' under a screwcap?

Posted by Charles Emilio, Feb 10, 2010.

Someone asked me this tonight and I could not provide an answer.
If a screw cap is 100% air tight how can air get in and influence the wine to age for better or worse?

On a sidenote, Is california releasing bottles $50 and above under screwcap?

thanks for any help


Reply by napagirl68, Feb 10, 2010.

Ok.. controversial subject here, Charles! To answer the second question, YES. many napa wineries are going screwcap cause they are tired of getting back cases of wine that are corked. Remember that the fungus spreads by spores (like mushrooms on your lawn). If you mow the mushroom, you spread the dry spores in your grass, and many others pop up. Same with the fungus that can live in corks- it can spread through specific lots of corks, or can spread from one tainted cork within a case. It is a horrible thing. It produces the chemical called (for short) TCA which taints the wine. I can give one example... Clos Pegase in Calistoga is going screwcap. And they produce cabs up over $100/bottle.

Ok, now for the controversial part. I, personally, drink 95% california wine. In descending order: Napa, Russian River, sonoma, amador, Oregon pinot gris and pinot noirs, and SOME Italian and French wines. I am addressing your question as a california wine drinker. Since cal. cabs need much less time in the bottle than a French bordeaux, I would hazard to say that that a screwcap would be ok for most cal wines. I have talked to people at UC Davis who insist the cork does nothing for aged wine but lend to over-oxidation and other problems. They say the main problem with going screwcap is the psychological. People love to uncork wine! They think that means it is good wine cause it has a cork. (This reminds me of the technology that has existed for years to make a quiet vacuum cleaner, but the test market thought the vacuum that was silent was ineffective.) And of course, there is the anticipatory celebration in working to remove a cork, and the resulting celebration to have a glass! I am not criticizing this in any way, just mentioning it as a factor. On the other hand, is the mystery of ingredients... the cork is indeed an ingredient in the wine, and may lend other nuances to the wine that cannot be labelled. Just because something cannot be quantified, doesn't mean it has no merit. So, you have to decide for yourself. The first question should be the caliber/quality of the wine, secondly, the corking method.

As for how a wine can age in a screwcap...In every bottle of wine is headspace... the wine is not filled to the top and vacuum sealed. So there is opportunity for natural aging (slow oxidation) to occur with the air that is present.

I think you should do some research... try UC Davis' site. And French sites as well. I know there are many purist who disagree with screwcaps, and I understand... I was a purist myself until I had to return almost 25% of my wine over the past 10 yrs due to cork taint...... I am willing to embrace the future, but would miss the cork. I suppose I am a bit on the fence. If I had had some, say, 10 yr old Napa cab with a screwcap to try, I might be a total convert. But for now, I go both ways. If it is a fairly young to drink wine, and a great one at that, I don't mind a screwcap at all. I just had one the other night that I loved, went back and bought 2 cases. But I think most winemakers are afraid to change things...

I am unsure about this, but what about irradiating the corks? As a scientific person, I deal with the utilization of companies that irradiate things... such as dog food, produce, etc. I know that is controversial with food, but with cork, I would think it would kill the fungus.. and preserve the custom of uncorking a wine...

Reply by Mark Angelillo, Feb 10, 2010.

Very comprehensive answer! Sounds like the industry needs to do a bit of testing to see. Maybe some forward thinking wineries can close some of their bottlings with screwcaps and most with cork, and try them horizontally in a number of years. Of course, there's always subjectivity, and I do appreciate a bottle closed with cork, but at least we'd have that information to look at.

Reply by penguinoid, Feb 10, 2010.

I'm a bit undecided when it comes to corks. I don't quite buy the argument that corks are inherently evil (as some new world wine producers seem to argue), but then again getting a corked bottle can be a pain. I certainly wouldn't choose to buy or not buy a wine simply due to the closure, though.

Thought this was interesting --

"Alan Limmer (pictured above) is one of the pioneers of the Gimblett Gravels, that special piece of vineyard land in Hawkes Bay. He’s also achieved recent celebrity status in the closures debate, where, as a trained (PhD) chemist he’s been able to provide some much-needed scientific rigour to discussions about sulfides, reduction and screwcaps.


"Of his involvement in the closures debate, where he became deeply unpopular in some quarters for suggesting that using screwcaps with very low oxygen transmission runs the risk of reduction problems, Limmer says that ‘it still occupies some of my time’. He began by writing articles primarily for winemakers and then saw that the whole issue was much bigger than this. He put out a newsletter saying that there might be some problems with screwcaps in 2002, and this was picked up by a local journalist. He was particularly scathing about claims by screwcap supporters that corks showed a one-thousand-fold level of variation in oxygen transmission. ‘You only had to look at it for half and hour to see that it was rubbish’.

" ‘Screwcapped wines harden up’, says Limmer. ‘They go into a tight ball’. He often does comparisons of cork-sealed versus screwcapped wines, and reckons that this is the best way to see the low-level reduction that hardens up the palate. ‘Most people don’t get a chance to see the comparisons’. Limmer is currently using Diam for his wines (a taint-free technical cork), but says that ‘if I could be sure of getting clean corks, I’d use them.’ He also says that the choice by some winemakers to use screwcaps for their whites but corks for their reds is not logical."

Still hard to know who's got it right, yet, I guess...

Reply by HokieWolf, Feb 10, 2010.

This has been the question and pause in my mind for years as to "How could it be a good wine if it has a Screwcap?" MD20-20, Boonesfarm....etc. While I have always loved the cork and the process of the removal and smelling the cork, yet today I now work at the second largest Wine producing Company in the USA and they have been using "Stelvin" caps for years mostly on their Value wines, yet recently on some extreamly good "Old Vine Zins" and I really like the fact that after 1 or two glasses I can still keep the Wine for longer then a couple days after opening. Yea I know, if it's that good...why wait? Drink it in one sitting. There are times I can't and for that reason I like the screwcap. How does the Screwcap vs the Cork effect the aging? As it was stated by Napagirl, there is head space and this allows what air is in the bottle to effect the wine. How? I am not sure, Yet I will pose this question to our Winemaker and Quality Control personel to see what they may say. Try the 2005 Cardinal Zin. Comes with a screwcap and retails for $20 a bottle, yet you should be able to get it for $13 on sale.... We bottled it and ALL the Zin drinkers at work LOVE IT!

Reply by GregT, Feb 10, 2010.

Charles - the flaw is in your basic assumption that air goes through the cork and that this is what "ages" wine.

That's not actually the case.

Think about it. Some wines have capsules. Some have wax coverings. Do those allow air exchange? Can air really get in if the cork is covered with a capsule?

Cork is wood. Each piece is different. You can get a statistical average and a likelihood of air exchange, but you can't state with certainty which specific cork will work in which way. They also come in different sizes. The best corks have been shown to allow almost no air exchange. However, there are wild variations in cork so it's essentially random.

Oxygen and air are the enemies of wine for the most part. You don't want them to enter the bottle. And to prevent the oxygen from having a negative effect on the wine, most winemakers add a bit of sulfur. That, plus the sulfur already in the wine, bind up the oxygen. So an important consideration is the amount of free sulfur and free SO2 in the wine at bottling. Because oxygen levels are entirely unpredictable, the winemakers have for a few centuries added enough sulfur to eliminate the possibility of too much oxygen transmission.

And that accounts largely for the reduction in wines under screwcaps. If you use the same sulfur treatment as you did with cork but you have no need for it, the sulfur stinks. So winemakers need to use less sulfur under screwcaps than under cork. However, remember the other variable - the free oxygen in the wine due to bottling.

The fact is that nobody can detail every change in wine as it ages. But one thing they know is that the amount of oxygen in the wine bottle varies considerably. In wine bottled on vacuum lines, you can have say, 0.6 parts per million. In wine bottled by hand, you have maybe 4.4 ppm. That oxygen is in the wine no matter what kind of closure you use.

When people didn't know about this, they didn't think about it. Now they know, so they have to think about it. Of course, the more knowledge, the less likely you are to be a "natural" winemaker, but that's my side issue.

You need some oxygen for the fermentation so the yeast and bacteria can do their work. Once they're done, you want much less oxygen. This is where things get interesting. One reason given for the long lives of old Spanish Riojas for example, is the fact that they spend so much time in wood, which gives them micro-oxygenation for several years. Too much oxygen gives the wine an "oxidized" flavor and in fact, you can detect that in some older Rioja.

Today, people use techniques like micro-oxygenation and bubble a tiny bit of oxygen in the wine while it's in tanks and they're accused of "manipulating" the wine or "hiding" the terroir. Mostly I think the people making those claims have no idea what they're talking about. In fact, the winemakers are only doing what was always done but in a more controlled way. However, even they aren't really in control - it's all guesswork at this point because nobody knows exactly how much oxygen to provide, whereas we have some experience with the barrel aging.

Then the idea of tannin polymerization is an issue, at least in aging reds. Wine is acidic and that environment affects the polymerization of tannins. As they link up, they become heavy and drop to the bottom of the wine as sediment. Interestingly, the same environment causes de-polymerization of tannins. So we have another variable to contend with because clearly the pH of the wine affects things. That specific reaction may be independent of oxygen, but it's also affected by oxygen if there's some around.

That also leads to the issue of color. In red wine, the color comes from anthocyanins and other compounds. The anthocyanins are from the skins and oxygen really affects what happens here. The juice starts out deep purple and as wine ages, becomes more red. With no air, the red color develops fast but it's not stable. With some oxygen, it's stable, and with too much, you lose color.

So what happens? Color researchers found that anthocyanins link with tannins and there are several catalyzing agents, including oxygen, but also including compounds like the aldehydes found in oak. But if you've got those, you don't want additional oxygen too or you end up with those oxidized, brown wines.

And remember that temperature affects the rate of all the reactions. So at higher temps, you may accelerate reactions that are undesirable to the point that they surpass the desired changes, and you end up with a wine that aged before it ever really matured.

In white wines, it's just as complicated. They turn brown. Why? I wish someone could explain that to me. All I've been able to come up with is that it's partly due to caramelization of sugars, breakdown of sugars and other compounds into more volatile compounds, Maillard reactions, which are basically reactions between proteins and sugars but which some people say are not possible because they need heat, and oxidation, or "rust".

The point is that there are many many reactions happening, and they're not due to oxygen transmission through the cork, although an imperfect closure that allows oxygen transmission will affect them. The French in Bordeaux have confirmed that some oxygen transmission is through the cork, but it's in ranges and it's unpredictable. You might note that the transmission rate is the same whether bottles are on their sides or upright. In addition, the Australians have many years of research on alternate closures. They've been working with them for over 20 years. Once again, unencumbered by silly traditions and fears, they lead the world. There is no reason on earth that a wine can't age gracefully and perfectly under screw caps.

For my own personal opinion, I think the continued use of cork is due to simple idiocy. We measure the sugar, protein, and acidity levels of our grapes, we control the fermentation temperatures, we use stainless steel tanks, we clean and disinfect our bottles and lines, we can measure dissolved oxygen and sulfur and nitrogen, and we put our "unmanipulated" and "natural" wine in wine coolers to keep them at the correct temp until we're ready to drink them. All of this is based on what we have learned over the years. I.e., science. We've incorporated modern technology at every step, even to the point of having a specific glass for a specific wine.

Then we draw a line in the sand and throw everything to the dogs. We keep corks based on tradition and fear and idiotic devotion to some notion that a closure deserves reverence! I don't know - pulling out a cork is about as romantic as unwrapping a new package of gym socks.

Anyway, here's some more to read:

Reply by VegasOenophile, Feb 10, 2010.

I think we all just have to get over the feeling that cork means upper tier wine and to be OK without that "pop" when a bottle is opened. Older wines will have that still for a while to come. I'd rather be surprised by how magnificent a wine can be with the bar set low because I am unscrewing the cap, vs. being monumentally disappointed after being excited for a bottle, then finding that it's been corked or otherwise somehow tainted.

Reply by zufrieden, Feb 10, 2010.

Great post, Greg. I can't see any good scientific reason for rejecting the screwcap closure. Aging is indeed a form of wine manipulation and is managed by knowing the factors affecting change in the barrel and bottle. If you are interested in controlling the aging process, you simply adapt your process to the different closure system. I for one prefer screwcap for convenience, purity of wine expression and providing fewer closure failures (have not had one yet with screwcaps). While it is sometimes a problem getting the sulfur situation under control with some screwcapped wines, that issue should fall away with experience and better understanding of the oxidation process.

Reply by rzakharov, Feb 12, 2010.

Strangely the discussion remains limited to only two options, namely natural cork and screwcap. There still exists an alternative of composite or plastic corks. While I am apprehensive of exposing my food/drink to prolonged contact with plastic/synthetic materials, for those who want the "pop" of the cork without the risk of smelling a wet dog or cardboard, these alternatives could be an option.

Reply by Cathy Shore, Feb 12, 2010.

Bearing in mind that around 95% of wine is consumed within 2 years of production, I don't see the resistance to screwcaps. After all, what other industry would accept its reputation being permanently damaged by the problem of TCA when it could do something about it? There is huge resistance to the screwcap here in France - mostly from Sommeliers who hate the idea. For wines that are drunk relatively soon after bottling it's a great idea to use a screwcap. For wines that require prolonged ageing I have to admit to being pro the traditional cork. As ageing is in effect a slow controlled oxidation over time then the cork wins out in this case but of course not without its problems. Wines bottled under screwcap can have the opposite problem - reduction. As for plastic corks - personally, I hate them. They strip the teflon off corkscrews, can't be replaced after use and an Australian winemaker I used to work with was very anti saying that as plastic is a polymer, wines bottled under plastic have to be very robust as polymers absorb aroma (her words not mine).

Reply by GregT, Feb 12, 2010.

Cathy - I think wine drinkers, at least those who drink more expensive wines, are a very very conservative group. Some of them like to think that they aren't but their actions belie them. In addition, there's a fetish aspect to wine for some people. They build elaborate and costly cellars that are meant to display as much, or more than, to serve a fairly pedestrian function.

Sort of like Bower Birds. And like them, it seems to be a male thing. It's kind of funny because most females I know who love wine are much less interested in displaying it.

Also, I've been told by some people that they find "romance" in opening a bottle.


Anyhow, as I posted, there is more to aging than simply oxidation and even the oxidative reactions are not necessarily all due to the cork, if any are.

And IF you want slow oxygen transmission, you can't put a cork in a bottle and expect to get it. You can only expect with some reasonable percentage chance that any given cork will allow X rate of transmission. Ideally, your cork is water and air proof, which is why it was used in the first place. In Bordeaux, they've measured oxygen transmission and it's all over the map, with some corks allowing a great deal and others allowing none. And the winemakers do not measure the transmission qualities of their corks before using them.

i don't know about the "polymer" argument either. Polymers are only complex molecules made up of repeated links of smaller ones - "poly", as opposed to monomers. They're certainly not all the same, whether "natural" or "synthetic" so it's not like you can make a blanket statement like she did. I don't think that statement is necessarily true. But I agree that plastic corks aren't all that great for a number of reasons, not least being the fact that they're hard to put in so some people use a slightly smaller one which of course, compromises the seal. I have a friend who imported some white wine corked w plastic and 30% of the bottles were oxidized and brown within less than a year.

rzakharov - it's limited in this discussion because that's what the original post said but if you ask me, the nicest looking closures are the German glass stoppers. Since we're able to make things to really fine tolerances these days, I'm wondering why we don't see more of those stoppers.

And regarding agglomerated cork, here's a quote from Cameron Hughes, who Greg DP is championing these days:

"The corks we are using are Neutrocork's from the world's largest cork supplier, Amorim. It is made using a similar process to the DIAM and is, effectively, autoclaved high-quality cork granules rebuilt with food grade (read: neutral) polymer. We started with DIAM's but moved to Amorim because their supply chain and QC are world class and their SOP's have pretty much been adopted across most cork supply chains. They are also available with consistent pricing around the globe.

I can buy regular cork for about the same price but choose not too. Why? Guaranteed no TCA or other objectionable compounds or phenols, incredible side-wall pressure to ensure consistent seal/no leakage, and consistent oxygen transfer rate. Wines have been aging beautifully under these closures for over 10 years but as you can imagine the real aging potential and final results of 20 years of aging are still down the road. Having used corks of this type for over three years now I am very confident in their performance across a broad range of wines. As a side note, I have never once seen one of these closures leak beyond 1-2MM."

Reply by Cathy Shore, Feb 12, 2010.

Thanks for that very interesting reply Greg. I agree with your sentiment about the glass stoppers - they look fantastic and reseal easily although my experience is limited to Gruner Veltliner from Austria with this type of closure. I imagine they are expensive to produce?

Like you say, wine production has moved, changed, adapted and reflected what we have learnt over time as we understand the 'science of wine' better. To reject change out of hand because of the lack of 'romance' involved is narrow minded.

Reply by GregT, Feb 12, 2010.

"I imagine they are expensive to produce?"

Don't know.

But they look so cool. Especially on top of those long German bottles.

Penfolds in Australia is trialing them as is Whitehall Lane in CA, or so I've heard.

Foro those who don't know what they look like, here's a pic:

Reply by mmrmaid, Feb 15, 2010.

i had a gorgeous pinot noir by sineann in oregon a year or so ago and they use a glass cork. i think it's brilliant>>no tainted wine and still sexy and romantic! go to
they talk about it on their homepage.

Reply by cbracerx, Feb 18, 2010.

Another vote for the "glass cork" - I have had several bottles of nice Cab from Whitehall Lane with these and they worked (and looked) great.

Reply by dmcker, Feb 18, 2010.

Winemakers from several wineries have told me for more than a decade that glass corks would be their preference, but there were (in the past, anyway) worries from them about price, product liability issues and general availability. Is this changing?

Reply by zufrieden, Feb 18, 2010.

I researched some recent developments in glass closures but cannot find a lot of text on liability and other related issues. For example, has anyone experienced a situation where such a stopper breaks and glass particles enter the wine? I would think that such an eventuality is a relatively rare event, but then I have almost no experience with this kind of bottle closure. On the surface, glass stoppers do seem elegant enough and are easily re-closed. But is this enough?

Perhaps a separate forum on closure types might be in order...

Reply by GregT, Feb 20, 2010.

If the glass falls into the wine, it will sink, so at least you'll know to watch out if you open your bottle and the stopper is chipped. But same goes for the bottle itself - if it's chipped by the corking machine, those pieces will fall. I suppose you're right that there's an issue, particularly in the US, but I've never heard of that as a real obstacle. I think the cost and re-tooling are probably bigger issues, and most of all, the conservatism and reluctance to change.

Had a screwcapped sherry last night. It's pretty expensive and there isn't much of it so the bodega didn't want to risk ruining the few bottles that do exist. That was encouraging. Of course, other parts of Spain have outlawed closures other than cork, as has much of Portugal, so the reactionaries are fighting hard . . .

Reply by zufrieden, Feb 20, 2010.

@GregT. I wasn't particularly worried about the invasion of glass chips or shards into the wine, but your reminder about chipped bottle tops was a good one. Again, I suspect that is quite rare as I don't personally recall a case of bottle neck chipping where the bottle itself was not also compromised.

As to the laws against the use of alternative closures in places like Portugal, one can only assume an interest group at work - likely the owners of cork oak bushes. As a renewable resource, cork oak might always continue to own some cachet, but as a raw material for closure I prefer the screw cap and (maybe) the glass stopper. Some premium producers in Burgundy and Chablis now regularly close some of their best bottles with screw caps and that practice doesn't alarm me in any way; in fact, like you, apparently, I applaud it.

Reply by GregT, Feb 20, 2010.

Most definitely an interest group at work. When I lived in Detroit I got to watch an interest group protect its industry. Long run, I guess it didn't really work out for them. I'm surprised about Burgundy tho. I would have thought they'd be holdouts.

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