Video about corks and bottles on my YouTube channel.
Let’s talk about the vessel that holds the divine nectar.
While I’ve discussed the contents of wine bottles extensively—and will continue to do so—today, let’s focus on the container itself. After all, wine can only be safely preserved and delivered to its admirer if housed in a perfect vessel.
The days of amphorae, barrels, and wineskins have long faded into history. Today, when we say “wine”, the image that comes to mind is a glass bottle sealed with a cork.
Glass bottles dominate the modern wine industry for good reason. Glass is an ideal material: it’s inert, completely airtight, affordable, and aesthetically pleasing. However, it does have some downsides. Glass is heavy and fragile, which increases the costs of transportation and storage.
Another challenge with glass bottles is storing wine once the bottle has been opened. To prevent rapid oxidation, a half-empty bottle must either be vacuum-sealed or filled with inert gas. Of course, there’s always the simplest solution: finishing the bottle in one sitting. But wine storage is a topic in itself, and we’ll discuss that separately since it deserves special attention.
In recent years, wine has also been packaged in plastic bottles and bags. These alternatives are lighter and far less prone to breaking. The bag-in-box option has an additional advantage: as wine is consumed, the bag collapses, preventing air from entering and slowing oxidation. Unfortunately, plastic is not as inert as glass. Unwanted chemicals can leach into the wine—slowly but steadily—and the material is also slightly permeable to air, causing the wine to degrade over a period of months. Plastic is only suitable for wines intended for quick consumption; it’s not a material for long-term storage, and, of course, not for maturing.
For now, there is no true alternative to glass bottles, still.
The situation with bottle closures is a bit more varied.
Cork remains the timeless classic.
Although cork closures look like a natural companion to glass bottles, the two have not always been together. The French only began using corks in the 17th century; before that, bottles were typically sealed with oil-soaked rags. The introduction of cork closures is often attributed to Dom Pérignon, the celebrated figure in winemaking. However, this is yet another myth. While Dom Pérignon contributed greatly to the art of winemaking, the cork closure is not part of his legacy. The true innovator behind this practice remains unknown to this day.
Corks are made from the bark of the cork oak—Quercus suber. This species is native to southwestern Europe and northwestern Africa. Today, most cork oaks grown for commercial production are found in Portugal and Spain. The trees must mature to at least 25 years before their bark is thick enough to be harvested. The bark is carefully stripped from the trunks, a process that does not harm the tree.
However, the cork from the first harvest is of poor quality—too rough and crumbly to serve as wine closures. Instead, the first harvest material is used for products made from cork granules, such as flooring, shoe soles, and such. After the first harvest, the tree regenerates its bark over the next nine years, and the subsequent cork is of much better quality, suitable for bottle closures. This cycle continues every nine years. Since cork oaks can live for around 300 years, a single tree can produce an impressive volume of cork throughout its lifetime.
Cork is well-suited for this purpose because it is lightweight and highly elastic. A cork can be easily compressed to fit into a bottleneck, and it will then expand to create an airtight seal.
For the cork to maintain its properties, however, it must remain moist. Before being fashioned into closures, bark is boiled to enhance its elasticity and then cut into individual corks. Once inserted into a bottle, the cork closure must stay wet to prevent it from drying out, cracking, and crumbling—ruining the wine inside.
If you store a bottle sealed with a cork closure, keep it horizontally! This ensures the wine remains in contact with the cork, keeping it moist. While this isn’t critical for short periods of days or weeks, prolonged storage of several months—or especially years—can cause the cork to dry out, risking oxidation and spoilage of the wine.
An agglomerate cork closure is a more affordable alternative to natural cork. Rather than being cut from a solid piece of cork, agglomerate closures are pressed from cork granules and chips. While they are cheaper, their quality is lower. Agglomerate corks dry out faster, crack, and crumble more easily, making them unsuitable for long-term storage. They are typically used for inexpensive wines meant to be consumed rather quickly.
The disadvantages of cork closures go beyond simply needing a corkscrew to open the bottle.
The main issue with cork closures is cork taint. The culprit behind cork taint is trichloroanisole (TCA), a compound produced by mold when exposed to chlorophenol compounds. Chlorophenols are often used in wood treatment as antifungal agents. If mold develops on treated wood, TCA can form. If TCA is present in or penetrates through the cork into the wine, it imparts an unpleasant aroma reminiscent of wet cardboard. This is certainly not the aroma one expects—or wants—in wine.
Historically, cork taint was a critical issue. While modern wood treatments have significantly improved, cork taint still affects around 3% of bottles worldwide.
Agglomerated cork closures are even more prone to cork taint than regular natural cork.
For many winemakers, a 3% wastage rate was unacceptable, which led to the search for alternatives to traditional cork closures.
The most direct alternative is the synthetic closure. These closures are cheap and easy to produce but have significant drawbacks. Synthetic closures are only suitable for wines that will be consumed within a year. They do not seal the bottleneck as effectively as cork and allow too much air to pass through, which causes the wine to oxidize prematurely. Furthermore, synthetic materials can leach undesirable substances into the wine over time.
Another alternative is the screw cap, typically made from aluminum. Screw caps provide an airtight seal, perfectly protecting wine from air oxidation and preventing any contamination. They are also easy to open and reseal, making them very convenient. Screw caps have become particularly popular in Australia and New Zealand, where they have almost entirely replaced cork closures.
Screw caps are ideal for wines where fruit-forward flavors dominate. These are wines that are meant to be consumed young and do not require extended bottle aging.
However, for wines that are crafted to reach their peak after years of bottle maturation, screw caps are not ideal. The issue lies in their complete airtightness. The maturation process of wine requires micro-oxidation—a tiny, controlled amount of oxygen to allow the wine to develop complexity and soften over time. Too much oxygen will spoil the wine, but without any oxygen at all, proper maturation cannot occur.
This is where cork closures excel. Natural cork allows a small amount of oxygen to pass into the bottle, facilitating the slow, gradual oxidation needed for long-term aging. This balance makes cork closures irreplaceable for wines designed to improve over time.
From a biochemical perspective, wine maturation and the role of closures in this process remain grey areas in winemaking. Much of the process is still unclear and requires further study. Many conclusions can only be confirmed empirically through observation and experience. However, screw caps have been used long enough to reveal that they negatively affect wine aging.
Interestingly, Australian winemakers, who were among the first to embrace screw caps and had almost completely abandoned cork closures, are now returning to cork for fine wines that require aging. At present, new-generation screw caps are being developed to allow a controlled flow of air similar to cork closures. Yet, the effectiveness of these innovations can only be confirmed decades later, since proper wine aging requires time, and so does evaluating its outcomes.
Finally, let’s mention the glass closure known as Vin-lok or Vino-seal. Its properties are very similar to those of a screw cap, providing an airtight seal, but it is more aesthetic in appearance. The only drawback is that it comes at a slightly higher cost.
Holy wars around the quality of wine closures continues at full speed. Despite the rise of alternatives, cork closures still dominate the global wine industry.
As a bonus to our wine closure discussion, let’s uncover the truth about corks used for sparkling wines. Why do they resemble a young porcini mushroom? Surprisingly, they don’t start out looking like that. An unused sparkling wine cork looks almost identical to a regular cork, only slightly longer.
So, what happens? The cork is gently compressed and inserted into the bottleneck, where it is secured with wire cages. Keep in mind that the pressure inside a champagne bottle is around 5 atmospheres—this intense pressure constantly pushes the cork upward. The wire cage prevents the cork from being forced out of the bottle.
Under these conditions, the cork exists for at least six months or longer. Thanks to its natural elasticity, the cork slowly expands against the wire cage, filling any available space and forming the typical “mushroom cap” shape.
When a wine lover finally opens the bottle and releases the pressure, the portion of the cork that was compressed inside the bottleneck relaxes and regains its original form, creating the “stipe” of the mushroom shape. A few minutes after opening, you’re left with a charming little porcini cork.