A short position statement on closures

So what's my current position on wine bottle closures? [This is a lenghy post I've just made to an online wine forum, in response to another post.]

There's no such thing as a perfect closure. It's about choosing the best closure available for your wine. If it were a simple matter of 'sealing' a bottle to stop liquid coming out, then of course there would be no excuse for continuing to use cork. There are a range of alternative wine bottle closures that are taint free. Take your pick.

But what we've learned - largely through the adoption of alternatives to cork - is that the oxygen transmission properties of the closure matter. And the precise level of oxygen transmission will affect the way the wine develops after bottling.

For an inexpensive wine that's likely to be drunk within a year or two after release, it's nuts to use natural cork, because cheap natural cork is nasty and carries a risk of taint. For these wines, synthetic corks, screwcaps with a saranex-only liner (there are two different liners for screwcaps, one of which allows very little oxygen transmission - the tin/saran - and one which allows more - saranex only) or Diam represent good alternatives.

Microagglomerates that have been steam-cleaned are also a good bet, although do carry a small risk of taint, as do steam-cleaned one-plus-ones (two discs of natural cork sandwiching an agglomerate core).

For more expensive wines that may be cellared, then it becomes more tricky. I'd say for high end, ageable wines then natural cork bought from the most quality-minded cork producers is the best option. This is because we like the way that wine develops under good natural corks.

I'm personally not keen on the tin/saran liner used widely for screwcaps. It just doesn't allow enough oxygen transmission. This means that there's a risk of reductive problems post-bottling (although the exact nature of this risk hasn't yet been quantified). It also means that the wine will develop differently to the way it develops under cork. Will it be better? How lucky do you feel?

Synthetic corks have developed quite a bit over the last decade to the point where they are claiming really good oxygen transmission characteristics. I'd like to see independent data on this. Likewise with Vino-Lok, the glass closure where the seal is by means of a plastic 'O' ring. It's certainly a functional and good looking closure.

Diam may prove suitable for long-ageing wines. I'm sure it's good for 10 years, because the Altec (the tainted predecessor using the same mechanical design) has shown the physical integrity of the closure is fine after this time.

Finally, a plea - let's try to be as informed as possible when we discuss this complex business of closures. I've found the whole debate to be unessecarily polaized in the past, with people splitting off into factions, and spouting propaganda at each other. For example, when we talk about 'screwcaps', let's remember that the screwcap isn't the closure, but merely a way of holding the liner in apposition to the rim of the bottle. It's the liner that determines the oxygen transmission properties of the closure.

Cork on TV: forest in a bottle

Tonight there's a prime time national TV show all about cork. Titled Cork, forest in a bottle, it's focusing on the environmental impact of abandoning cork for alternative closures such as screwcaps and synthetic corks, and it will be shown at 9 pm tonight on BBC 2.

A quick recap on the issues surrounding corks and their alternatives. Cork is a wonderful natural product, which does a great job sealing wine bottles. It's only as we've moved away from cork to alternatives that we've found that the technical requirements of a wine bottle closure are not all that simple. What cork does (and this seems to be important), is to allow a slow release of oxygen from its compressed cellular structure for the first few months after bottling, and then a very low level of oxygen transmission from then on, through the cork/glass interface. The level of gas transmission by a sound cork seems to be just enough for optimum wine development, but not too much (in reality, it's hardly any at all).

But cork has a real problem: trichloroanisole (TCA) taint. 2,4,6-Trichloroanisole, the major compound responsible for musty taints associated with cork, is formed in cork bark by the chemical combination of phenolic compounds with chlorine. These phenolic compounds are naturally present in bark as a result of the breakdown of lignin, a hard substance giving bark its rigidity. The chlorine can come either from the environment, or from fungi living on or in the bark.

We’re incredibly sensitive to TCA and its chemical relatives, and can detect them at very low concentrations. It makes wines taste and smell musty, like old cellars, or mouldy bread, or damp cardboard. Some people can detect TCA at concentrations as low as 2 ng/litre; others don’t recognize it at 10 ng/litre.

This makes life very hard for the cork industry. There’s no easy way to spot a good cork from a bad one, and so winemakers have either had to resign themselves to losing a certain percentage of the wines they seal with cork to taint, or switch to cork alternatives such as screwcaps and synthetic corks. Many winemakers choose to remain with cork.

The good news for them is that the cork industry is responding to criticism and doing something about natural cork quality, trying to understand the causes of TCA and also to devise ways of removing it.

There are two rather different, yet complementary, approaches to dealing with TCA. The first is to use quality control measures to try to prevent contaminated cork from being turned into closures that then leave the factory. The second is to assume that TCA will be present, and to then remove it by some sort of extractive or washing method – the curative approach. Put both strategies together and substantial reductions can be obtained even if either strategy is not 100% effective alone.

The current rates of cork taint? About 3.3% - this is the figure from the International Wine Challenge faults clinic, which is the world's largest blind tasting, and includes wines from all over the world (this is the percantage of those bottles sealed with natural cork). It's likely that the rate was higher in the late 1980s and early 1990s, but the hope is that as the quality control measures and curative strategies that the leading cork companies have taken begin to show up in terms of lower taint levels, the rate of cork taint should drop to much lower levels.

It is largely because of the pressure put on cork companies by the success of alternative closures that these strategies have been put in place. Without alternative closures as competition, it is likely that we'd be stuck with much higher levels of cork taint. Winemakers have a responsibility to source cork only from those companies that are serious about combating taint.

The future? Cork is a wonderfully sustainable product with a low carbon footprint. The cork forests really are beautiful, and because wine stoppers are the most profitable use for cork, using cork this way sustains rural communities and helps preserve these ecosystems. But the wine industry can't take the hit that it was taking in terms of ruined bottles in the late 1990s all in the name of sustainability. If the rate of cork taint really is on the way down, then there's certainly a future for cork, but as just one of the closure solutions alongside a range of alternatives.

What has saved cork so far is that fact that sealing a wine bottle so that the wine tastes good when it's opened isn't a trivial matter of just 'sealing' it. If screwcaps, for instance, did exactly the same job as cork, then it would be stupid not to switch straight to screwcap for all wines: they don't have musty taint issues, and they are a lot more convenient because you don't need a device to open the bottle.

Another corked wine: the lenticels?

Another corked wine tonight (not that I'm getting many these days). I looked at the cork - once again, it had angry looking lenticels. I'm beginning to thing that the lenticels are the source of the problem with corks: where they run across the face of the cork, does this increase the chance of cork taint? Interestingly, this tainted wine had some mustiness, but also some sweek oaky notes (even though this was an unoaked rose).

What's new on wineanorak, and some corky encounters

After a long period of no corked bottles, two in three nights - a Rioja and a serious Fiano were struck with musty taint. The Rioja cork had a big, ugly looking lenticel running through its wine-side face (pictured). Could this be the reason? I guess lots of microbes live in the lenticels (the gas-excange pores running through the cork bark), and its these that produce the musty taint, presumably.

Anyway, an update on the recent articles posted on the main wineanorak site, for those who just look at the blog:

• A full report on the recent Domaine Leflaive masterclass
• A review of Charles Metcalfe and Kathryn McWhirter's book on Portuguese wine and food
• A too-lengthy report on visiting New Zealand's leading biodynamic estate, Millton
• What to look for in a wine

Making corks

Spent yesterday morning at Amorim's labs with Dr Paulo Lopes, who's a scientist working on issues such as oxygen transmission by closures. It sounds nerdy and dull, but it's really important. Paulo did a presentation on efforts by Amorim to deal with the taint issue, then he presented his work on how much oxygen ingress there is with each type of closure.

Then it was time to see a couple of cork manufacturing and processing plants. High-end corks are still punched by hand (top picture), a skilled task where rapidly taken decisions about where to punch the next cork from have important quality implications. The corks are then sorted either automatically, or manually (above). The best quality corks can cost more than a Euro each (below) - and they look beautiful. The modern cork production process is a fusion of the modern (e.g. gas chromatography screening for minute TCA levels) with the traditional (cutting cork bark, hand punching corks).

Wine faults in Denmark

I'm currently enduring that special part of hell also known as Gatwick South Terminal, en route to Billund in Denmark, where tomorrow I'll be presenting a paper on wine faults at the XXth Entretiens Scientifiques Lallemand. I've never been to Denmark before, and seeing as I'm coming back tomorrow evening, I doubt I'll see much of it. Apparently, Legoland is in Billund.

Most of my talk will be based on the last three years' data from the International Wine Challenge. These data have been collected by Sam Harrop MW (pictured), who is a co-author on this paper, and they're really exciting. The strength of this data set is that it's large (c. 15 000 wines opened, 10 000 separate wines entered); it's a 'real world' analysis of faults; some reasonably smart palates have been involved in getting the data; and there are multiple years' worth of data to look at. The weakness is that it's sensory analysis and not chemical, and also that faults such as reduction and brettanomyces may well be under-reported, as well as the possibility of false positives.

One of the exciting things about the paper is that it will contain a regional breakdown. Some countries are over-delivering oxidized wines, bretty wines, and wines with reduction defects.

There's a limit to what I can say about the data here, because they aren't mine to share. But I can say (and these are provisional figures from an ongoing analysis, so please don't quote them elsewhere) that cork taint is hovering around 3% all three years. Screwcap reduction is around 2.5%, but going down. With 2008, it seems that winemaking faults are overtaking closure faults as the chief cause of problems. Around 7% of wines entered into the challenge show some sort of fault, which isn't really good enough.