Why are corks used to seal wine? What does “corked” wine mean? Are corks better than screwcaps? Sometimes questions come up about wine closures…specifically cork so we thought we would educate on them a bit.
First, where do corks come from? It comes from the bark of the Quercus Suber tree, which is a bit sponge like. These trees primarily come from Portugal, but many have also been planted in nearby Spain. These trees can grow up to 60 feet high with a 12-foot circumference. The great thing about cork trees is that they are sustainable since they do not need to be chopped down. After the spongy bark is harvested from the standing tree, they continue to slowly regrow their bark. A cork tree can be harvested once every 9 years.
After being harvested, the bark is boiled to sterilize and reshape it. Then, the corks are punched out of the cork bark into the shaped enclosures we know today. After being cut, the corks are washed, cleaned, sterilized, dried and shipped to wineries and bottlers to be used. It is important to sterilize the corks to avoid TCA. We will discuss that more in a minute.
Originally, wine was sealed with cloth and leather, followed by clay and sealing waxes. In the 1500’s, glass tops started to be used but the glass had to be hand blown to fit each specific bottle since there was not a uniform size. It was in the late 1600’s that a more uniform glass bottle shape started to be used. This is when cork became the sealant of choice.
Corks are a great sealant since they keep “almost” all of the oxygen out of the bottle. Oxygen getting to the wine will cause it to oxidize and turn into vinegar. However, since corks are porous, they allow a small amount of oxygen (1 milligram per year) in. This is a good thing since it allows the wine to develop some complexities and soften the tannins over time.
What about alternative closures? Today, we see aluminum screwcaps used on many wines. Australia and New Zealand started using these in the 1970’s. Since then, many wineries all over the world have chosen to use screwcaps. These are great for the easiness of opening. Since the screwcaps have an internal seal, oxygen is not able to get to the wine. As we mentioned before, this is a good thing to avoid oxidation. However, it does not allow any air in so it is still a bit unknown how different wine types will age. We think the screwcaps are great for wines that are meant to be drunk young and not aged. They do a great job at keeping these wines fresh.
There are also synthetic corks which are made of plastic or sometimes a hybrid of plastic and pressed cork. These are less expensive than traditional corks. The issue with synthetic corks (besides being difficult to open!) are that they do not create a perfect seal so they can oxidize the wine prematurely.
Traditional wine corks are not perfect though. As we mentioned earlier, they can have TCA if not sterilized correctly. TCA, which is short for 2,4,6-trichloroanisole, is a contaminant in wine. Have you ever poured a glass of wine and when you go to smell it, you smell musty aromas? These aromas can remind you of a moldy basement, wet cardboard or dirty gym socks…definitely not what you want to smell in your wine! This is what people are talking about when you hear them say a wine has cork taint or is “corked”.
From the 1950’s to the 1980’s, certain insecticides and fungicides called halophenols were commonly used. When the halophenols come in contact with certain bacteria, fungi and mold, it creates TCA. Many cork producers do not always know if the bark or soil are contaminated. If the resulting corks are, they contaminate the wine.
The contaminated wine is harmless for people to drink but it will not taste very good, so you will probably not want to. In higher doses, TCA has the musty aromas but in smaller doses, it mutes the aromas and flavors of the wine so it just seems “off”.
It is thought that 3% to 6% of all corks have TCA. This equates to up to 1 billion bottles of wine ruined by this contaminate a year. Cork suppliers are getting better about testing individual corks or throwing out a whole batch if one cork is found to have TCA. This is starting to help lessen the amount of “corked” wines. At one point, up to 10% of wines were contaminated.
TCA is not just a wine problem either. It has been found to affect produce that is shipped in contaminated wooden or cardboard boxes, such as, apples. Some liquors, such as, Grey Goose vodka, use a cork enclosure. They also experience cork taint at times.
Even though cork is not perfect, it will most likely remain the wine sealant of choice for a long time. There is a certain tradition and romance to opening wine and hearing that pop or hiss. Cheers!