I recently attended a symposium in London on the subject of wine closures. The panel discussion concluded a seven-year debate on the pros and cons of different wine closures. The panel consisted of four world-renowned winemakers and was moderated by Jaime Goode the “Wine Anorak”. Now admittedly the winemakers were all southern-hemisphere new-world winemakers but they all unanimously condemned natural cork as a product that belongs firmly in the past. It was, perhaps, a shame that there wasn’t an advocate of natural cork on the panel, but it seems hard to find a natural cork advocate who isn’t involved in the supply chain.

Why did corks receive the scathing ire of such a distinguished panel?

Well, firstly, there is the age old problem of TCA, 2,4,6 trichloroanisole, a chlorine based compound which can be detected in the most minute quantities and gives the wine an off-smell likened to a dank basement or mouldy socks. Despite the best efforts of the cork industry TCA in natural corks still hovers at about 3%.

Here is the nasty little molecule thanks to wikipedia

Apart from TCA, cork stoppers can lead to a few other problems.

Random oxidation; in order for corks to work optimally they need an internal moisture level of about 5-7%. Any less and they loose the springiness needed to seal the bottle. If that seal is lost then it will lead to ingress of oxygen into the bottles and oxidation of the wine. Oxidation of wine is similar to watching an apple go brown; the wine goes brown and loses its life and vibrancy.

Flavour Scalping; the cork absorbs some of the volatile aroma compounds in the wines changing its character.

Bottle Variation; probably the most insidious problem of natural cork, a batch of wine all bottled on the same day will have qualitative variations between the bottles and different development over time.

The final problem, as I see it with natural corks is the people who make them. To this day I have yet to meet a cork supplier who was willing to take responsibility for the damage caused to my wines, or anyone else’s for that matter. I estimate that in the past 14 years that I have been in business the spoilage rate due to cork for our wines is about 5%, and that is quite conservative.

If we try to quantify the damage, then a quick estimate of our production over the past 14 years stands at about 5.5 million bottles, if there was 5% spoilage due to corks then about a quarter of a million bottles were affected. If we do a quick calculation to quantify this in monetary terms then the loss is 250,000 times, say, $8 average (wholesale) for a bottle of wine, which equals $2 M.  Will I ever see this money back form the cork industry? You tell me…

The problem becomes even more insidious as most customers do not even realise that the wine has a cork taint. Often I have had to argue with restaurant staff trying to explain that wine is spoilt and they haven’t understood a word I was talking about. The upshot is that you might taste a wine that you don’t like and never buy it again but the problems may have nothing to do with the way the wine was made or stored, it might have been spoilt due to a faulty closure.

Personally cork problems haunt me all the time. Part of my job is to go out and promote our wines at talks and tastings. I know that I always have to take more bottles with me than I will need as I can never be sure that all the bottles will be showing at their best. I always taste every bottle closed with natural cork before every tasting. In a prestigious press tasting in New York a few months ago I had to throw away a bottle of Zinfandel ($35 retail) because it was corky.

It is often the case that when on the road I have to pull bottle samples from customers’ warehouses, whilst I try my best to supply my export markets with the freshest vintages, it is not always the case that I get my hands on the freshest wines. Sometimes we can pull an older white where dodgy corks have played havoc; the usual problems are TCA with natural cork or premature oxidation with plastic corks.

The situation is intolerable, in what other industry is there such a high failure rate, and even more absurdly in what other industry would such a high failure rate be accepted but its consumers?


So what are the options? Well the answer is not as clear-cut as it seems. Alternatives to corks do exist, the most visible being the screw cap, but there are other stoppers such as synthetic corks, glass stoppers, and technical corks.

Many advocates of alternative closures will swear by screw caps, insisting that they are the best solution for sealing wine bottles. However screw caps bring with them a whole host of problems. With metal tops, tolerance levels for a perfect seal are very tight so if the cap is applied poorly then the seal can be compromised and the wine will rapidly oxidize. On the flip side the virtually airtight seal offered by a screw cap can lead to reductive qualities (caused by the lack of oxygen) in red wines, which will be characterized by aromas of burned rubber and bitumen in the wine

Plastic corks work well for short periods of time and are probably suitable for wines that get drunk within a year of bottling, unfortunately my experience is that despite our best hopes and efforts a lot of wine does not get consumed in that window. It is a fact I usually discover when I am out of town in a store doing a tasting and the wine on the shelf is one that I had shipped more than a year prior, despite prioritisng the latest vintages for export. In addition plastic corks are a derivative of the petrochemical industry, which raises its own set of problems.

We have tried twin top corks, a granulated cork body with natural cork discs on the top and bottom of the cork. Our experience was that the batches we were sold were really difficult to extract, the corks would often break in half during extraction and the levels of TCA were not reduced.

Some years ago we were offered a new technical cork called the Altec, it was supposed to offer a miraculous solution, a cork like device that was specially treated so there would be no TCA. Alarm bells should have started ringing when we discovered that the corks wouldn’t actually fit all the way in the bottle but this was further exacerbated when we discovered that TCA levels were off the chart.

We have tried expensive natural corks where the manufacturer promised that they had used special treatments to prevent TCA. Initially the results were pretty good but as time passed the quality of the corks fell significantly.

That is my experience with cork manufacturers, they will move heaven and earth to try to persuade you that their product is the best on the market and they have propriety systems in place to remove TCA, they will wine and dine you and pay for you to come and visit them in Portugal. They will ensure that the initial shipment is tip-top, and then slowly they will start to decrease the quality of the corks in subsequent shipments. It is a very simple thing to do, corks come in bags of 1000 pieces so you can easily add some lower standard corks without anyone noticing and increase profitability per bag. I have challenged my suppliers on this point and never really been given a satisfactory answer. You can always request a pre-shipment to check quality but who is going to send rubbish in a bag that they know is going to be highly scrutinized. We also run quality checks on the finals shipments of corks as we do with all the raw materials we receive but the testing of corks is particularly time consuming and costly.


A sterile sealed bag of corks.


Today we have moved to a technical cork called the Diam cork. It is a granulated cork where the cork bits have gone through a process of supercritical carbon-dioxide which removes he TCA in the cork, look at it as decaffeination for corks. Our success rate with this new stopper has been very high, we have not needed to re-tool our bottling line as they behave like normal corks, there is no dust and I have not come across a single bottle of wine with any TCA. We now bottle all our wines up to the estate series, and all our whites throughout the portfolio. Someone writing in one of the local wine forums described the cork as a cheap, chip cork, he wasn’t to know that it was one of the best wine closures you can find on the market today.

Using Diam I can confidently open any bottle of wine and know with almost absolute certainty that the wine is just as the winemaker intended. I would like to try to use them for our premium wines but I realize that there is certain consumer reluctance to see anything but natural corks in a premium bottle of wine, so the irony is that my most expensive wines will be sealed with the worst of all closures, and that is indeed a shame.

It is obvious to me that the future of wine closures is not natural cork, as we know them. It will probably be a combination of screw caps with a diam cork liner or some derivative thereof and the industry will benefit as a whole. It will probably take a few years, the wine-industry is incredibly conservative and change is frowned upon.

If you feel a need to support the cork industry for ecological reasons then insulate your roofs with cork granules use it to cover your floors and walls or buy shoes with cork soles, but please be careful with it in your wine.


Cork top tip!

If you do come across a bottle of wine that is obviously corky, add a piece of cling film / saran wrap to the wine. It will strip the TCA (along with some other flavour compounds in the wine) but will render the wine drinkable.