Anyone who has popped open a bottle of wine will agree that it is one of the few sounds in the world that brings true joy to the listener.
For nearly three centuries, cork has been used to seal virtually every bottle of wine. Since the 1970s though, that dominance has come under attack by other forms of closure such as screw caps, plastic seals and glass stoppers. Wine closures are a $4 billion business worldwide. Each year, 20 billion closures go into wine bottles and increasingly they are not corks.
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Let’s explore what can be known from this battle for the bottleneck?
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Short History of Corks
Cork is one of the most mysterious and, in a lot of ways, one of the most wonderful products that nature has made. It is nature’s nearly perfect product. It’s very light. That’s why it’s been used for fish floats and buoys. In fact, that was its very first use and Cork has been used for about 4,000 years. And as a way to seal wine containers, it was used for about 1,000 years — from 500 BC to 500 AD. Then, for 1,000 years, it wasn’t used as the world went to different things and trade collapsed after the fall of the Roman Empire. About 1600 it came back into use. And it, as you say, it has been the monopoly closure for close to 400 years. Throughout history, cork has always been considered almost a magical product. In the 17th century, 1660 to be exact, there was an English scientist by the name of Robert Hooke, who was with The Royal Society of Scientists in England. He had developed a new microscope and, as part of the work, he went around and he picked up different products. They were just day-to-day products, like a piece of shell, and he looked at that under a microscope. Then he picked up a feather and looked at that under a microscope. Cork was one of the things that he also looked at under a microscope. When he cut the piece of cork off, he looked at it and was absolutely amazed at the structure. He saw millions and millions of little things that were kind of rectangular boxes. These boxes reminded him of a monk’s cell — a place where a monk prays and sleeps. So he said, “Let’s call those things cells.” That is the derivation of the word cell — as the building block of all living things. It goes back to cork.
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Though cork harvesting has been a practice since the ancient Greeks, it wasn’t used in glass wine bottles until much more recently. Like wine, cork comes from a living, breathing organism: Quercus suber, or the cork oak. Amidst the frenzied yearly cycle of the wine industry, these evergreen oaks move like sloths, slowly expanding and growing the bark, known as orange cork.
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With an average lifespan of 200 years, each tree can provide thousands of bottle stoppers when cared for properly. The short version of the cork life cycle goes like this: Happy cork trees grow to age 25 in semi-arid forests surrounded by other animal and plant life on the Iberian peninsula and North Africa. After that, skilled cork harvesters use axes to slice off the outer bark of the tree, leaving its inner wood intact and undamaged. Then, the planks of cork bark are dried, sorted, and processed. To make the bottle stoppers we know so well, slices of cork are boiled to remove impurities (like the chemicals that cause cork taint) and dried until they reach the optimum texture to be pressed into bottles. Over nine years, the outer bark slowly regenerates before the next harvesting cycle begins. Cork oaks are the only oak whose bark regenerates in this fashion, making Quercus suber a very special tree.
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Why only Cork?
Wine sealed using a Cork severely retards the oxidation process, allowing the wine to age and evolve slowly over time. This takes place because Corks, or better put, quality Corks allow a minimal amount of oxygen into the wine. This is important because when air interacts with wine, it causes the wine to eventually oxidize. A minimal amount of air needs to interact with the wine because that is how wines develop their mature, secondary qualities as well as expel unwanted aromas. The best corks allow close to 1 milligram of oxygen to enter the bottle each year. This is just the right amount of air to remove the sulfites that were added in the bottling process to keep the wine fresh and to avoid the harmful effects of oxidation. This small amount of air is perfect for helping age-worthy wines develop their complexities.
Cork performs extremely well under pressure. With some nudging, cork can compress to half its size, without bulging out the other side or increasing its length. Ok, so there are a lot of things that can do that if you push them hard enough, but the key here is cork’s resilience. Cork’s insides look like a honeycomb filled with gas-89.7 percent gas, which in fact makes it both light and buoyant. And the cells that make up the honeycomb are insanely stretchy. So the cells can stand to be squeezed tight—like by, say, the skinny neck of a wine bottle. But cork doesn’t collapse under the abuse. Although the gas in the cells is compressed and loses volume, it is always pushing back, which allows it to seal cabernets and champagnes.
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Challenges with Natural Cork
Wine corks do however have problems, the major issue being infection with TCA, which causes what is known by wine collectors and others in the wine business as Corked Wine. Trichloroanisole, TCA is created via a series of chemical reactions in the bottle: chlorine from the environment reacts with the natural lignin molecules in the woody cork to make trichlorophenol, which is in turn methylated by mold. TCA has one of the most potent aromas in the world – some people can smell as little as 2 parts per trillion in wine. So, in every eight cases of wine, one or two bottles will smell like wet cardboard or simply not taste their best. This is why restaurants let you taste the wine before pouring – to let you judge if the wine is tainted. Corked bottles of wine remains a serious problem in the wine industry as many people think that it affects between 5% to 10% of all wine undrinkable. Somebody who spends $400 for a bottle of wine, takes the cork out and blah — they don’t want to drink it.
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Alternatives for Natural Cork
Synthetic Corks are made from polyethylene, the same stuff as milk bottles and plastic pipes. In the beginning of the synthetic era, artificial corks did not prove themselves. The problems with synthetic corks are the lack of a perfect seal. In turn that allows more unwanted air into the bottle, causing the wine to oxidize. Worse, many of the synthetic corks have been known to impart a slight rubber or chemical smell, damaging the wine. With the failure of Synthetic Corks, producers who preferred Natural Cork used DIAM, small brother of Natural Cork. DIAM is made from natural cork, but instead of using large sheets of cork bark to make the cork, the cork is produced from small pieces of cork particles that have been glued together to form a cork. DIAM also reduced the risk of TCA infection. But, anyhow it must also be taken from Cork oak tree which takes nine years to give one production cycle.
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After years of research and development, Synthetic Corks now perform nearly the same as the natural version with three good exceptions: they have no taint, they let in a bit more oxygen and they are very consistent in oxygen transmission. Their consistency is a major selling point to winemakers because the wine will have a predictable taste at various points in time. In fact, winemakers can tweak the oxidation rate of their wine by choosing from a range of synthetic corks with different rates of known oxygen transmission. Screwcaps are actually two parts: the metal cap and the liner inside the top of the cap that seals to the lip of the bottle. The liner is the critical part that controls the amount of oxygen getting into the wine. Back when screwcaps were only used on jug wine, there were just two types of liners available. But today multiple companies are jumping in to offer their take on what rate of oxygen transmission is best, as well as to replace the tin used in one of the traditional liners. The standard liners admit either a bit more or a bit less oxygen than good natural corks. Screwcaps, being manufactured, are also very consistent.
Plastic Corks | Image Source: Winefolly
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Is there an optimum wine closure?
The Performance of manufactured closures, made with 21st-century technology, is excellent. Generally, they approximate our expectations, based on over two centuries of experience aging with natural cork closures. For the regular wine, you might purchase for dinner this weekend or to keep for a year or two, any of these closures are perfectly good, while the manufactured closures avoid taint. In fact, your choice is more a matter of preference for opening the bottle. Do you want the convenience of twisting off the cap, or do you want the ceremony of removing the cork?
For long aging however, the only closure with an adequately long track record is natural cork. So to be safe, that is the closure to choose. Once we have solid long-term evaluations of synthetics and screw caps, it will be possible to judge their suitability for extended aging, such as more than ten years.
Over centuries, winemakers have consistently taken advantage of new technology to improve their product, from oak barrels to bottles to modern crushing and pressing equipment and micro-oxygenation. While manufactured closures have some key advantages, it is proving difficult to displace natural cork due to its centuries-old tradition, albeit with a few problems, and its connection to the natural environment.
- “A Chemist Explains Why Corks Matter When Storing Wine” in Winefolly.com.
- “Why Cork Is the Most Amazing Material in the World to Keep Your Wine Tasty” by Rachel Swaby in Gizmodo.com.
- “To Cork or Not to Cork: The Wine Industry’s Battle over the Bottleneck” in knowledge.wharton.upenn.edu.
- “Wine Corks Everything You Need to Know About Wine Corks” in thewinecellarinsider.com.
- “What is Cork and why is it used to close wine bottles?” by Laura Burgess in vinepair.com.