Diam, Corks, Screw Caps

Written by Franz Weninger on the 17th of April 2017

Some of you may have noticed that we have been using Diam corks more and more in the past few years. How did this come about, what does it have to do with screw caps and were the corks at the beginning of 2000 really so terrible?

Yes!! Around 2000 - 2004, the quality of corks in Austria collapsed once and for all. We had to reckon on up to 10% cork failure due to TCA contamination. A further problem was the diminishing flexibility of the corks due to the new cork treatment substances used in an attempt to combat TCA. This also led to brittle, crumbly corks in addition to the tannin issue. (The more elegant our wines became, the more we noticed that corks also give off tannins in the wine, which can be positive or negative.) This is why we too began looking for alternatives and have been bottling some of our wines with screw caps.

Screw Caps

The results were relatively poor. At the time, we were in the process of converting to organic, and our vineyards had to contend with a lot of cover crop competition. This meant that there was only little oxygen present which the yeast was able to use, and so our wines became very reductive. It presented a challenge to us, because this is a phenomenon which actually arises in all organic or biodynamic farms during their conversion phase, sometimes sooner, sometimes later. Go and taste some of the relevant vintages and you will see. The wines bottled with corks seemed to be less problematic as this porous material lets in oxygen and also contains oxygen, thereby lessening the reductive character little by little. Further complicating the matter was the fact that Austria started using screw caps from Germany, where tinfoil was incorporated into screw caps (the Germans adopted this idea from the Australians, in their “fight against oxygen”) in order to block even more oxygen. In Old World countries, when screw caps are used, they use Saranex – the material which is also found in crown caps (for example the ones used for beer).

Saranex, Saran, tin

For a long time, we tried to get the upper hand over this issue through cellar work – by using less sulphur before bottling and more oxygen during vinification. A lot of measures were taken, but we did not achieve our goal through all this cellar work – instead we lost some quality, especially elegance.
What I found fascinating is that our wines from rocky (oxygen-rich) soils had a much lower reduction potential than the wines from the loamy (oxygen-poor) soils. Therefore, the pH levels pf the soils did not play a role. Since the year 2000, we have been purposefully forgoing sterile filtration, which is why there is always lees present in our wines. It keeps the wine young, as we say. I find this minimal reductive character desirable when it comes to our Blaufränkisch. It allows the wine to fully open up in a large glass or decanter, and to mature for a very long period. Now, one could counter with the argument that there are new screw caps that have been developed which have various oxygenation rates, and by using them I could also stay true to my style of wine when using screw caps. True, I could. But there are some “soft facts” which I’d like to mention here. Cork is a soft material. It has a balancing effect: it takes up pressure and also releases it again. One can observe these qualities in all aspects of winemaking, such as bottling. If the screw cap machine is only slightly off, it can cause considerable problems. The pressure of the caps as they are applied to the bottles has to be correct, otherwise one can end up with bottles which, in the worst case, leak or let in too much oxygen.
Another potential source of errors is the process of packing bottles into boxes. If two bottles bump against one another at their screw caps, the screw caps may become dented, leading to rapid oxygenation of the wine.
But corks also have a forgiving nature when it comes to the wine. They absorb and release. Reductive wines benefit from some oxygen. Wines leaning towards the oxidative end of the spectrum gain additional stability through the phenols present in the corks – however, these are not always a positive contribution.


“DIAM corks guarantee drinking pleasure without any cork taste. The ground cork is first sieved to remove all wood components before it is put through the Diamant process which cleans out any harmful chloranisoles. No chemicals are used during this cleaning process. It also reduces the microbial load and stabilises the material without removing important elements such as waxes. A further advantage is that no solvents or glues are used. Instead, the ground cork is mixed into a pulp with food-grade polyurethane and then baked under heat and pressure.”
That is what the producer had to say about the secret behind Diam corks.
This is why I began experimenting with Diam a few years ago. The process sounded consistent and I was especially convinced by the wines I had tasted which had been aged under this cork for 10 years. Our first results also appeared very promising. We first used Diam with our Blaufränkisch and for our special bottlings. Since the 2015 vintage, I have also been using Diam for our single vineyard wines. The fact that Domaine Leflaive recently completely converted to Diam helped to justify our decision. Even in Austria, there are more and more winemakers choosing this type of closure.

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