Cork, and other closures for Wine

‘You hate these, don’t you, Dad?’ We were at dinner, my son was holding up a cork from a wine bottle, and he had heard me complain about these pieces of bark many times. Too many times, apparently.  I love wine, but I suppose Benjamin was right, traditional whole-bark corks have caused me so much trouble in my work that I do hate them. My heart sinks a little when I take the foil off a bottle and see the top of a bark cork. Why?

Whole bark corks were an ideal way of sealing wine when it first started to be put in glass bottles, hundreds of years ago. The bottlenecks would have been inconsistent in diameter and shape, and cork has the rare quality of being able to re-expand almost immediately to fill a space, making it the ideal packaging solution - in 1750, or perhaps even 1950. Corks were used to stopper all kinds of bottles, in fact; aspirin, cough medicine, olive oil.

Now there are a number of alternatives, but the bark cork holds a particular mystique in the wine business, particularly in some markets (such as the US) and particularly at higher prices. Merely by association, many consumers of fine wines expect them to come with bark corks; they always had, after all. Why not maintain this antiquated tradition?

The first thing a packaging material should do is preserve the product contained in it. Everything else should come second; if the product is harmed by the packaging we need to find an alternative. Bark corks harm wine in two ways, one of which is fairly well understood, the other not. ‘Corkiness,’ or contamination by a chemical called TCA, is a problem for any liquid stoppered by cork. TCA is formed in cork at minuscule levels when microbes in the bark interact with chemicals containing chlorine, such as the wood preservative used on wooden pallets, or pesticides used around cork trees. We are sensitive to TCA at extraordinarily low levels, as low as 2 parts per trillion, or even lower; it is not toxic, but at low levels it masks other aromas and flavors, and at higher levels it gives the wine a ‘moldy basement’ smell. Not acceptable in either case, obviously. Twenty years ago I would say that one bottle in 12 was at least slightly affected, which was an absurd defect rate at the turn of the 21st century; now it’s more like 2-3%, better but still not acceptable. 

The second problem is worse. Bark is a natural material, which is part of its appeal. As a natural material it varies in structure; a perfect cork can limit the passage of air past it so well that some wines age successfully for as long as 50 years, but not all corks are perfect, even the very expensive ones. This means that the odds are that if you open a dozen bottles of a fabulous old Bordeaux or Barolo you will almost certainly find a lot of variation among them, due to varying levels of oxidation. You have a right to expect that your bottles of wine will be consistent; I like artisanal wine, but not artisanal packaging. Cork suppliers have progressively reduced the level of TCA-affected corks they sell, but there is nothing they can do about oxidation variation.

Notice that both of these defects, TCA and cork-caused oxidation, are often relatively subtle, which makes them hard to spot without a lot of practice, and very hard to identify as defects. This is in stark contrast to food defects, for example, where the product would typically look and smell awful. The wine won’t taste horrible (except in the case of very corked bottles, which can sometimes be smelled across the table), but it won’t taste the way it should; you won’t get your money’s worth. Our work as wine merchants involves opening the same wines repeatedly, which makes spotting these problems easier, but few consumers have that opportunity.

The good news is that there are excellent alternatives. The first  ‘closure’ on my list would be the one with the least romantic consumer image, the screwcap. The reputation of the screw-cap as wine packaging has gone from ‘Oh my God, never!’ to ‘well, maybe for the rosé I’ll be drinking in the park’ in the last few years, but the truth is that screw-caps are an excellent closure for all kinds of wine, fancy and not. There is of course no risk of ‘corkiness’ from the closure as there’s no cork, and there is almost no risk of variable oxidation either, as the cap is formed precisely onto the bottle at the bottling line. The newest screw-caps have a range of liners, that suit them to a range of wine types; some allow no air through, and some allow a tiny amount, comparable to a good cork but consistent. The use of this closure for very good wine is not controversial at this point, with the possible exception of the small amount of wine that is kept for many decades, only because we don’t have very many examples of very old wines to know either way. We love screwcaps. 

Drawback: the local markets of some Old World wine producing countries are very resistant to the idea of screwcaps, which makes persuading our Italian producers to use them a challenge.

The other main whole-bark cork alternatives are stoppers that work like corks, but are made of other materials. We like two brands in particular for the way they protect wine; ‘Diam’ is a stopper made of small grains of cork that have been cleaned of TCA with a proprietary method (similar to that used for de-caffeinating coffee) and mixed with a food-grade resin. These will always have Diam stamped on the side (or an M for Mytik in the case of sparkling wine corks). Another example is Nomacorc, their Select Green closure is made of a sugar-cane base and works very well to protect the wine. Again, the brand will be stamped on the side. Both of these work very well, in our experience; no TCA, and very high consistency of structure, so no random oxidation either. 

Drawback: you still need to use your cork-screw.

Is cork better for the environment than other closures? The cork industry has made much of the argument that their product is ‘greener’ than the others, mostly because the demand for cork means that the cork tree forests in Portugal and elsewhere are maintained. I am a life member of the Sierra Club, but this argument isn’t sustainable; ruining at least 3% of the wine packaged by a product (due to corkiness) and an unknown further amount due to random oxidation is a waste of all the effort, materials, and energy used in the production of that wine. When the wine is shipped around the world the math gets even worse. 

We love wine, and we want to make sure that the wine we import and sell reaches our customers in the best possible condition. For this reason, we are working to persuade our producers to switch from bark cork to better alternatives. We don’t generally try to tell our producers how to make wine, that’s their job, but we are very vocal about how they package it. I hope I have explained why.

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Written by Oliver McCrum