Jamie Goode: Cork versus screwcap (again)

Last week I was fortunate enough to attend a cork versus screwcap tasting in London, held by Stephen Browett of Farr Vintners, one of the top fine wine brokers and retailers in the UK. He’d managed to get together 25 mature wines bottled under both cork and screwcrap so we could taste them side by side blind. It was a very interesting exercise and the gathered tasters, all of whom have considerable experience with wines of all styles, voted on their favourites. Two take-homes: one was that even experienced tasters disagree; and, two, the results were all over the place. For some wines, screwcap was vastly preferred, while for others sometimes the cork-sealed wine won. It’s complicated.

There’s a further issue here. The screwcap is not the closure. It’s just a means of holding a liner or wadding in contact with the neck of the bottle, and this is what seals the wine. It’s the properties of the liner that determine how much oxygen it lets in (the oxygen transmission rate, known as OTR for short). For almost all screwcapped wines a liner called saran/tin, with a metal layer in it, is used. This has an OTR of almost zero. For some wines, a Saranex-only liner is used, which allows a bit more. Many of the screwcapped wines in the comparative tasting were sealed with a Saranex liner. You can tell the difference because these liners are white, and the saran/tin ones are shiny metallic in appearance: look inside the cap.

A further matter in question is that in many of the cork-sealed bottle, a closure called Diam was used. This is a technical closure made of small granules of cork, cleaned from taint, and then glued together. These come in three main types: Diams 5, 10 and 30, offering a lower OTR seal as the number goes up. Cork itself shows natural variability in terms of OTR. Immediately we see this is a hugely contentious topic.

Let’s backtrack. How did we get here? There was a time when all wines were sealed with cork. Alternatives were tried in Australia in the early to mid-1970s (screwcaps with a range of different liners, including cork, but these never took off), in Switzerland screwcaps became popular in the 1970s onwards for whites, and then in the mid-1990s plastic corks began to be used in Australia and California. The motivation for alternatives was cork taint: the musty defect from fungal-derived molecules in the cork. By the end of the 1990s these taint rates had grown, apparently because more wines were being bottled and this was putting pressure on the cork sources in Portugal and Spain. The Australians and New Zealanders were being sent some awful corks, and so the move to screwcaps, after some trials in 1998 and 1999, followed by 14 Clare Valley producers moving to screwcap together with the 2000 vintage, was rapid. Before long, almost all wines in Australia and New Zealand were being screwcapped.

Plastic corks turned out to be problematic. The injection-moulded models did a good job of keeping wine in, and were taint-free. But people soon found out that plastic allows oxygen to diffuse through it, and so the wines soon began to oxidize. Newer versions that were based on extrusion were a bit better, but still had the problem of high oxygen transmission. So it turned out that it’s the screwcap that became the true alternative to cork.

With the alternative closures, suddenly the lens was turned on post-bottling wine chemistry. A famous comparative closure study from the Australian Wine Research Institute compared a range of closures with the same wine (a 1999 Clare Valley Semillon) over a five-year period. Among other things, they concluded that if you use a closure with a different level of OTR, from that moment on, you have a different wine. Wines develop differently under different closures. Some of the wines sealed with a tin/saran-lined screwcap began to develop subtle reductive notes, because the volatile sulfur compounds in the wine were changing form in the absence of any oxygen. The plastic-cork-sealed wines oxidised fast. Overall, the screwcap seemed far the best closure, save for the very subtle reductive notes.

How much OTR do we want from a closure? The answer remains elusive. Studies have shown that a wine sealed hermetically in an ampoule will still develop, but more slowly, and it will develop reductive characters. Reducing OTR doesn’t just slow the development of a wine; that wine ends up going places that other wines won’t. Bottling with more headspace air/oxygen doesn’t avoid reductive characters developing, it just causes some oxidation, and is not the answer. Adding copper to fine the wine isn’t the solution either: it may get rid of some of the reductive issues in the short term, but they can still emerge post-bottling, and there’s a danger of oxidising some good wine components.

But it’s also a myth that corks breathe. The ideal cork behaves similarly to a tin/saran-lined screwcap and lets very little oxygen through. But one thing corks do is that they have oxygen dissolved in them that they release very slowly.

Which is best? Cork or screwcap?

Screwcap has the benefit of being taint free, and also cheap. For many wine styles, this seems to be the ideal closure, and from a consumer and restaurant point of view they are easy to open (although fancy sommeliers may feel deprived of the chance to demonstrate their cork-removal skills). Some markets are happy to pay top dollar for screwcapped wines; others seem insistent that fine wine should be cork-sealed.

Cork has the benefit of pole position: the fine wine world’s icons are cork sealed and there is a rich tradition of ageing wines under cork for many decades, and we like the results. It is also more aesthetic and it’s a natural product. But it is also inconsistent and expensive, and cork taint is still with us. Why should we stick with it? The only answer I have is that some wines taste better when aged under a good cork. Is this proven? Not really, but it’s my experience that wines sealed with different closures taste different, and for some wine styles, the cork really works well. For others, screwcap works better. It is, to reiterate, complicated.

More on the same contentious subject here.

• Jamie Goode is a London-based wine writer, lecturer, wine judge and book author. With a PhD in plant biology, he worked as a science editor, before starting wineanorak.com, one of the world’s most popular wine websites.