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Cork versus screwcap versus glass: the closure war and TCA taint

The way a wine bottle is closed seems a detail, but it is one of the most hotly debated issues in the world of wine. Cork, screwcap or glass stopper - each closure has its supporters and opponents, and the choice really affects wine aging and the risk of faults. A real closure war is going on: traditionalists defend cork, pragmatists praise the screwcap, and premium wine producers experiment with glass. In the background lurks TCA, that is cork taint, spoiling up to 10 percent of wines under cork. In this post you will get to know the three main closures, their pros and cons, what TCA is and why a screwcap does not mean cheap wine. It is a journey into a seemingly trivial, but fascinating issue. Let us start with why the bottle closure matters at all.

Why the closure matters

The bottle closure is not only a way to keep the wine from leaking - it is a factor that really affects its development and quality. Key is the question of oxygen. Some closures, like cork, let through minimal amounts of air, which lets the wine slowly age and change in the bottle. Others, like screwcap or glass, are almost airtight, which slows aging and preserves freshness. That is why the choice of closure matters especially for wines intended for long cellaring. The second key issue is the risk of faults: some closures, like cork, carry the risk of taint (TCA), others do not. The closure thus affects three things: the pace of aging, the risk of faults and the cost. It is not a trifle, but a deliberate decision of the producer. Understanding the role of the closure is the key to this post. So let us get to know the three main kinds, starting with the classic - natural cork.

Cork - the classic and tradition

Natural cork, made from the bark of the cork oak, is the most traditional and recognisable wine closure. Its action is clever: cork expands within the bottleneck, sealing the liquid and keeping oxygen out, while at the same time its tiny pores let minimal amounts of air interact with the wine, which over time can transform the aroma and flavour. It is precisely this controlled, slow exchange of oxygen that makes cork the best choice for producers of wines intended for aging. Cork also has a cultural and ceremonial dimension: the characteristic sound of pulling the cork, the ritual of opening, are part of the wine experience. That is why the best, most expensive wines are almost always under cork. Cork has, however, a serious flaw, of which more in a moment: the risk of taint. Despite this it remains the gold standard for wines for long cellaring. Cork is the classic, tradition and controlled aging. It is a closure with a soul, but also a risk. So let us get to know its greatest weakness - the TCA taint.

TCA - cork taint

The greatest flaw of cork is the risk of taint, that is so-called cork taint, caused by the compound TCA (2,4,6-trichloroanisole). TCA affects mostly materials of wood origin and forms when chlorine comes into contact with certain fungi during the processing of the cork. Although TCA is harmless to health, this compound can transfer to the wine and cause aromas of wet cardboard, damp basement or wet dog - spoiling the wine and masking its fruitiness. It is a serious problem: past studies estimated that TCA affects up to 10 percent of wines under cork. This means that one in ten bottles under cork could be tainted to some degree. Wine with cork taint is muted, flat and unpleasant, and the fault is not the wine, but the closure. It is precisely the TCA problem that drove the search for alternatives to cork. Although the cork industry has greatly reduced TCA thanks to new technologies, the risk still exists. TCA is the Achilles heel of cork, the main reason for the closure war. So let us get to know the most popular alternative - the screwcap.

Screwcap - the pragmatic choice

The screwcap is a modern, pragmatic alternative to cork, which revolutionised especially the world of white wines. Its greatest advantage is the elimination of TCA: the cork taint that spoils so many wines under natural cork is almost nonexistent under screwcap. It is a huge benefit - the screwcap practically guarantees the wine will not be tainted. The second trait is airtightness: screwcaps are almost completely airtight, and the wine under them ages much more slowly, which is fantastic for fresh white wines, but sometimes frustrating for reds that need oxygen to mellow the tannins. The screwcap is also convenient: it is easy to open and reseal, without a corkscrew. Contrary to prejudice the screwcap is not a sign of cheap wine - many excellent wines, especially from Australia and New Zealand, use it by choice, for quality and certainty. The screwcap is pragmatism: certainty, freshness and convenience. It is a closure that breaks stereotypes. Let us get to know one more option - the glass stopper.

Glass stopper - the elegant alternative

The glass stopper, known by the names Vinolok or Vinoseal, is an elegant, though lesser-known alternative. These glass closures look like something out of a perfume bottle and crown luxury rosés, boutique white wines or limited-edition dessert wines. Their greatest advantage is the combination of aesthetics with functionality. From a technical standpoint glass closures are airtight like screwcaps, so they do not carry the risk of taint (TCA). This gives certainty of no cork taint, like a screwcap, but with a much more elegant look. The glass stopper opens and closes easily, without a corkscrew, giving convenience and prestige at once. Its disadvantage is cost: glass closures are more expensive than cork or screwcap, which is why they are used mainly in premium wines, where the visual impression also matters. The glass stopper is a niche, combining the lack of TCA with a luxurious look. It is a choice for those who want the certainty of a screwcap and the elegance worthy of cork. The glass stopper is an elegant compromise in the closure war. It is proof that alternatives can be beautiful. We write more about wine faults in our post on how to spot a faulty wine.

The aging dispute

At the heart of the closure war lies the dispute over wine aging. The key difference between closures is their oxygen permeability. Cork lets through minimal amounts of air, which lets the wine slowly age and evolve over the years. Screwcap and glass are almost airtight, so the wine under them resides in an almost oxygen-free environment and, as is believed, is longer lived, but ages much more slowly. And here the controversy begins. Supporters of cork claim that only it ensures proper, classic aging of wines intended for long cellaring, especially reds needing oxygen to mellow the tannins. Supporters of the screwcap reply that airtightness better preserves freshness and eliminates the risk of faults, and long-term studies have shown positive results for wines under screwcap. It is still a hot, unresolved topic in the industry. The aging dispute is the essence of the closure war: does wine need a touch of oxygen, or is it better in airtight isolation? The answer depends on the type of wine and the philosophy of the producer. It is a debate without a clear winner.

Three closures in a table

Let us set the three main wine closures side by side:

The table shows that each closure is a different compromise. Cork allows slow aging thanks to minimal oxygen exchange, but carries the risk of TCA. The screwcap eliminates TCA and preserves freshness, but slows aging. The glass stopper combines the lack of TCA with elegance, but is more expensive. There is no single best closure - there is only the best for a given wine and goal. It is proof that even the bottle closure is a deliberate decision. The closure war continues, because each has its reasons.

Why it is worth knowing this

Understanding wine closures enriches the appreciation of wine and helps in practice. First, it helps recognise cork taint (TCA): knowing that notes of wet cardboard or damp basement are a flaw, and not a trait of the wine, you can return a faulty bottle. Second, it breaks prejudices: the screwcap is not a sign of cheap wine, but a deliberate choice for quality and certainty. Third, it helps understand why some wines are under cork and others under screwcap - it is a matter of purpose and philosophy. Fourth, it makes shopping more conscious: a screwcap is often a guarantee of the freshness of a white wine. A conscious wine lover knows that the closure is not a detail, but a factor affecting flavour and certainty. Next time, opening a bottle, it is worth thinking about what closes it and how this affects the wine inside. It is knowledge that deepens the understanding of wine and protects against misunderstandings. The closure is the last guardian of wine before the glass.

The key points in a nutshell

The choice of wine bottle closure really affects aging and the risk of faults. Cork, the classic and tradition, lets through minimal amounts of oxygen, letting the wine slowly age - which is why it is the choice for long cellaring, but it carries the risk of cork taint (TCA, a compound giving notes of wet cardboard, affecting up to 10 percent of wines under cork). The screwcap eliminates TCA and preserves freshness thanks to airtightness, great for white wines, although it slows aging - and contrary to prejudice it does not mean cheap wine. The glass stopper (Vinolok) combines the lack of TCA with elegance, but is more expensive, hence in premium wines. The dispute over oxygen and aging still continues. Want to judge wines and recognise faults? Keep tasting notes in the GustoNote app. See also our posts on wine faults and on whether wine improves with age.