jamie goode's wine blog: Wine closures: do we need a new screwcap liner?

Friday, July 10, 2009

Wine closures: do we need a new screwcap liner?

In short, yes.

Screwcaps are great, but in all the discussion on the topic (which has generated a lot of heat), one thing people keep forgetting is that the screwcap is not the closure. It's merely a way of keeping a liner (the actual closure) in apposition to the bottle rim. A crown cap does the same.

Now this sounds geeky and pedantic, but it's actually incredibly important. The gas transmission properties of the liner are crucial, because this determines how much oxygen gets into the wine after bottling.

There are two liners used for wine. The most commonly encountered is one with a metal (tin) layer in its construction, as well as a layer of saranex, which allows very little oxygen transmission. This is the one used in Australia and New Zealand almost exclusively.

The other is saranex-only. This allows more oxygen transmission, by a factor of 10. It's commonly used in Europe, especially for more commercial wines.

How does cork compare? Corks vary in their oxygen transmission (OTR) properties, but typically they fall somewhere between the tin/saran liner and the saranex-only. For the technical minded, Jim Peck of G3 in California has published the following guideline figures based on his research with a technique known as MOCON.

Typical OTRs in air (cc Oxygen/closure per day)
Screwcap, tin/saran liner 0.0001
Screwcap, saranex liner 0.001
Natural cork 0.0005
Synthetic cork 0.005

What are the implications of these figures? Do we want any closure OTR? The answer seems to be yes, just a little, to avoid problems with sulfur compounds (reduction). Othwerwise, as little as possible seems to give the best results for most wines.

The tin/saran liner is risky. It doesn't really allow enough OTR to reduce the risk of reduction to an acceptable level. Winemakers often have to resort to copper fining when they use this closure, which isn't ideal. Otherwise, it's great for shelf life and keeping wines fresh for a long time.

The saranex liner is great for wines that are going to be drunk in the first three to five years after bottling. But it's not really suitable for wines that will be cellared for longer.

So we have a need for a liner with properties somewhere between the two, and this is just what Jim Peck and his colleagues at G3 have been working on. Their solutions? Microperforations in the tin layer of the liner.

They have developed a mathematical formula that allows them to predict the level of OTR depending on how many perforations are made and where they are located. This could be great news for winemakers who are currently unprepared to switch to screwcaps because of the risk of reduction, or for winemakers already using screwcaps who are unhappy making the foot fit the slipper in terms of preparing their wines differently to suit the closure they are bottling with.

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At 10:45 AM, Anonymous www.rebeccagibb.com said...

Hi Jamie,

I agree with you: of course we need a new screwcap liner. We can't just accept screwcaps - as they stand - are the ultimate closure.

Most screwcap producers have been telling us they're on the verge of bringing out different transmission liners for some time. But where are they? Mañana, mañana.

Rebecca Gibb

At 11:43 AM, Blogger Clive said...


I absolutely agree. Its something that we have been asking about for a while.

I wouldn't totally agree with you in regard to having to copper wines. I'd say that most modern winemakers are often scared sh**less of oxygen and if they relaxed a bit they may have less problems.

Clive Dougall

At 2:26 PM, Anonymous thethe said...

I don't know about you guys, but I guess that everytime that man tries to mess around with nature, the outcome is always the same: it's almos perfect, but... Don't waste time looking for silly solutions, use what nature has given us and that has worked for hundreds of years.

At 2:34 PM, Blogger Randall said...

In a perfect world, there might exist a "smart" liner, one that was relatively permeable in a wine's youth but got progressively tighter as the wine aged. (Perhaps this closure had a a small redox probe attached to it w/ a smart chip that set permeability to a clever redox algorithm.) Failing that, I still believe that if one does not begin w/ high levels of disulfides or thiols in the wine and SO2 levels are relatively low, there is not a great likelihood of "reduction" problems being a persistent problem w/ very tight closure. Over time, thiols gradually change back into disulfides and "problem" goes away. So-called reduction "problem" may in fact be the precursor to a class of very interesting odiferous molecules that make us love some Old World wines as much as we do.

At 11:46 PM, Blogger Vinogirl said...

Nice to hear the science behind the closure debate. Thanks.

At 11:45 AM, Anonymous Anonymous said...

"So we have a need for a liner with properties somewhere between the two,..."
But as far as I understand from Jim Peck's achievements, a closure with such a specification already exists:...Cork!!! So why to complicate?

At 5:51 PM, Blogger Laurie Tadayon said...

Your post about screwcaps made me think about a recent post on Eric Asimov's NY Times "The Pour" blog. He recently conducted a blind tasting of Gruner Veltliners that prompted a whole backlash of comments.

One of the commenters discussed the prevalence of screwcaps on Austrian wines.

Here's what he had to say:

"Screwcaps are great, maybe too great: They really do prevent oxygen from entering the bottle. We had a recent tasting in which we aerated a bunch of Austrian whites, and the difference was dramatic: They really came alive with oxygen contact.

When I think back on it, I have always recommended that Gruner Veltliner wines receive thorough aeration before consumption. I’m thinking in particular of the ‘99 Nigl GV. We used to tell customers to open them on the morning of the evening they planned to drink them and aerate them, then pour them back into the bottle. By evening, they’d be in ideal condition for consumption."

In another comment he goes on to say that he thinks Eric's tasting might have been affected by not aerating the wines properly, especially the screwcapped ones.

It's an interesting argument against screwcaps, provided you do not aerate properly.

At 7:09 PM, Blogger Randall said...

Alas, I just don't think you can have it both ways. Mineral wines (whatever that means and mechanism still unelucidated) such as GV will always be tighter, more unyielding, whether they have a screwcap or a cork. The question is really: Is it too much of a good thing, and maybe that gets down to how the wine is going to be used. If you are planning to age a wine, there is absolutely no question in my mind that the tighter the closure, the greater the prospects for longevity (and concomitant complexity). If you are going to be consuming a "mineral wine" in the relative short term, a tighter closure will exacerbate the qualities that we love about mineral wines, or at least make it a bit of a logistical challenge (remember to open wine day before service, etc.)

At 11:15 PM, Blogger UCDWino said...

To all those who say that "nature has already solved the problem".. I wish that were true - even if cork taint could be eliminated, corks are still extremely variable in terms of oxygen performance. In fact, the one study I have seen where they pressure-tested the corks - they showed that 45% LEAK gas - not diffusion - LEAKAGE. http://www.scorpex.net/ASEVClosures2005RGibson.pdf - see page 45

The larger problem is that corks hide behind the "average" numbers in most articles (this one included) Screwcaps with tin liners are MUCH more consistent, and the saranex liners... less so. - in fact saranex liners have been shows to have 2/3 the variability of corks... not much of an improvment..

There is a LOT of work to be done in this field to be sure.

At 11:25 AM, Blogger Oscar Foulkes said...

Screwcaps certainly have their pros and cons. I love the way that the lifespan of Sauvignon is extended - I've had several screwcapped 2007 South African sauvignons recently that have tasted great. Often older whites under cork can get a kind of wet cardboard flavour, which I find extremely off-putting.

The problem comes with reds, which can be totally unyielding for a long time after bottling. One assumes there is a corresponding extension to the life of the wine. Given that Cloof is a predominantly red wine property it's an issue that does concern me, especially from the perspective of the wines' immediate enjoyability for consumers.

I love the dependability and user-friendliness of screwcaps, but their anaerobic properties can be a double-edged sword.


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