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In this episode of “Wine 101,” VinePair tastings director Keith Beavers discusses the difference between the two most popular wine closures: corks and screw caps. Beavers details the brief history of corks, which were originally popularized in the 17th century.

Though the screw cap was initially used for spirits and liqueurs, Australian winemakers began experimenting with screw caps in the ‘70s in an effort to avoid TCA, or cork taint. The screw caps have since taken off worldwide and are even used for sparkling and age-worthy wines.

Tune in to learn more about the debate between corks and screw caps.

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Keith Beavers: My name is Keith Beavers and is cold soup considered a meal, or is it an appetizer? Or is it just a snack?

What’s going on, wine lovers? Welcome to Episode 26 of VinePair’s “Wine 101” podcast. My name is Keith Beavers, and I am the tastings director of VinePair. It’s Season 2, and how are you doing?

Screw caps. Corks. Or should I say screw caps versus corks? No, no, no, no, no, these are two different things. We are going to talk about the two of them and we’re going to get rid of some myths. We’re going to get into it.

I’m having a little bit of an issue on how to begin this episode because with the amount of time I’ve been in the wine industry, I was a witness to not the introduction of the screw cap, but the implementation and the evolution of its technology and its acceptance in wine culture. I don’t know where you are in your wine journey, but you could say, “Keith, I remember that. That was tough. We’ve come a long way.” Or you could say, “What’s the problem? I drink wine with a screw cap all the time. What happened?”

Well, let me tell you the story of these two wine closures, because that’s really what they are, wine bottle closures. We’ll get a sense of where we’re at with the debate because if you don’t know, it was a debate. It’s still going on, but kinda not. Let’s get into it.

A cork for wine is a small piece of bark, basically, from a tree. That tree is part of the oak family — the same family that makes barrels, just a different species. The thing about this particular species of oak is that it has a very finicky environmental preference, if you will. It grows best in sandy soils free of any chalk. It prefers an annual rainfall between 15 and 30 inches, and it would really like temperatures never to fall below 23 degrees Fahrenheit. We would like to have our elevation between 300 and 1,000 feet above sea level, thank you very much.

With those nature demands, man, the oak tree for cork oak really can only thrive in the western Mediterranean. Even there, specifically in Portugal, parts of Spain, and maybe North Africa — but it’s really centered in Portugal, specifically in the Alentejo region, which we talked about in the Portugal episode. Here, they have almost 2 million acres of cork trees, which represents about 34 percent of the world’s cork trees. That’s a lot, and they also produce half of the world’s corks. Wow.

When these trees turn 25, they are ready to yield commercially useful cork for the industry. Every nine years in the summer — this is according to Portuguese law — a cork tree is stripped of its bark. A hectare is a little over three, almost three and a half acres. The average hectare of a cork forest can yield 500 pounds of cork. It’s all science, but this particular cork is special because it has a specific cell structure that brings the corking material to life.

What they do is they take this cork and they actually boil it for, I think, 90 minutes to make it flexible, but also to kill a bunch of molds and bacterias. The wood is then rested, sorted, and cut into the corks, and then those corks are polished on each end. At this point, they used to bleach the corks to sanitize them, but recently, they found that bleach or chlorine can actually increase the likelihood of TCA being formed in the cork, which we talked about in the Wine Faults episode.

Actually, today it’s more common to use hydrogen peroxide, which I think we all know is used for cuts and bruises. Then, they’re graded for aesthetic, basically, for the visual quality of the cork. The more natural markings on the cork, the lower the grade. The fewer the markings, the higher the grade. Here is where if the cork needs to be branded for a winery, it’s done. Then, the cork is coated with a silicon film to help make it easier to get out of the bottle. They’re then put into bags dosed with wine’s protector, S02 as an antibacterial agent, and they need to be stored in an odor-free environment with a temperature not going above 68 degrees F and for the humidity to not exceed 70 percent. Just like the shock of S02, these conditions are helping to prevent the formation of TCA. They really don’t want this stuff to form.

Corks range between 1 and 2.3 inches. The longer corks are meant for bottles that are going to age for a long time, which makes sense. They’re going to hold up for a longer period of time. For well over two centuries, this has been the primary closure for wine bottles. It’s been around much longer than that. There is evidence that the ancient Greeks and Egyptians both used not only amphora for closures onto the amphoras vessels, but they also used large cork covered with pitch to actually close those amphora vessels. Yet, it was in the 17th century where if you look at some of the art back then, you can see that wine was basically still stored and served in barrels.

However, also in the 17th century was the innovation of glass. As glass became more popular, glass decanters became popular as somewhere to put your wine in. Then, of course, there were stoppers for those decanters so it would not oxidize or flies wouldn’t get in. They were glass stoppers that were formed to fit specific decanters, and then they were threaded. Also, in this century it was realized how expensive glass was, so the use of cork became more common.

The thing is, during the Middle Ages, cork wasn’t really used that much because the Moors had control and conquered the land where cork trees were and they didn’t drink wine. This was a comeback. The cork came back in the 17th century to become one of the primary closures of wine bottles, but this was before the corkscrew was invented. What would happen is corks would be put halfway into bottles so you could get them out. Of course, then the corkscrew was invented, and everything changed.

So, cork is popular. It’s the No. 1 way to close your wine bottles. There is this running thought that the cork is porous. Therefore, the small amounts of oxygen and gas exchange that happens between the outside and inside of that bottle help a wine age. There is a debate there, and we’re going to get into it in a second, because as modern technology became more available, there was a heightened awareness to the extent to which how many wines were actually corked at any given time. It was a little bit alarming. Also, there is more communication in modern times, so there was more understanding of bottle variability, but the big deal was TCA, cork taint. That was the enemy.

As Jancis Robinson puts it in the “Oxford Wine Companion,” it’s because of cork that we actually do age wine today. It was the thing that allowed us to do that, even though it has issues. If it wasn’t for the cork in its natural state, we wouldn’t actually have wines that evolve. If you were worried about cork taint and you wanted to create a different closure for wine, you would have to check all the boxes that you liked for cork. The seal would have to be reliable. The substance would have to be inert in that if the wine came into contact with it, no crazy reactions would happen. The ergonomics would have to be sound. Easy to open, easy to close. Easy to insert and put back in. It would also be nice if it was relatively inexpensive to produce. And of course, the big deal, it can’t have the ability to form TCA.

In the late ’50s, there was a French company that had a screw cap called the Stelcap Vin. It was used primarily as a closure for spirits. Always forward-thinking, the Australians. In 1973, a company called Australian Consolidated Industries bought the rights to this specific closure. They were worried about cork taint, so they renamed it the Stelvin cap, and they began to experiment with this new technology.

A screw cap is basically two components. It’s an aluminum alloy, metal cap attached to a sleeve. The second component, which is a very important component, is the plastic wadding on the inside of the cap. This is called the liner. It usually contains a layer of tinfoil that acts as a barrier for gas exchange. This is the thing that doesn’t allow oxygen to get into the wine. Over the tinfoil is a layer of thermoplastic and this is the inert surface the wine can interact with.

As we learned in the Sulfites episode, aluminum and wine interaction can get a little stinky. In the early ‘70s, Australian Consolidated Industries experimented with this thing called the Stelvin cap. In 1976, they published the results of their study. What they showed was that the screw cap is actually ideal for sealing wine bottles if the wadding material is satisfactory. They had four reds and four whites with a screw cap, one with a cork for comparison. Each screw cap had a different wadding in it, so they were just trying to figure out how it would work. It came to the conclusion that when the wadding is right, the wine is sound. Of course, this was very exciting so Australia was going to focus on corks.

They started moving towards this as being the standard closure for their wines. There was a big push for it, but it didn’t work because TCA still wasn’t fully understood and there wasn’t much consumer acceptance because people liked the romance of a cork. There were people in the industry asking, “Wait, corks help wine age. Why would you put a screw cap?” It wasn’t really until 2000, when a group of winemakers in the Clare Valley of Australia, known for its Riesling, had enough.

Their wines are very susceptible to the lack of aromas that cork taint produces. They got together and produced a vintage, but with a screw cap. The problem was those bottles and those caps are not available in Australia yet, so they actually had to get everyone together and buy 250,000 bottles from a company in France. They made a big to-do about this. It made headlines, and everything gained momentum. I actually read that six years later, some of those wines were uncapped or unscrewed, if you will, and they’re aging just fine. This actually prompted the island a few thousand miles away, New Zealand, to create the New Zealand Screw Cap initiative in 2001.

By 2004, around 70 percent of the wines in New Zealand were under screw cap — up from only 1 percent three years before. Something’s working. By 2014, 95 percent, and 80 percent in Australia. An entire country is primarily under screw cap with their wines — and the wines are good, or sound, I should say. There’s no cork taint, and the screw cap isn’t just like screwed onto the bottle after it’s filled, the sleeve is held down tight on top of the bottle of the machine. Then, these pressurized rollers come and they mold the sleeve or the cap to the ridges on the outside or the top portion of the bottleneck where the little threading is.

The cap itself is still attached to the sleeve, but with those little perforated bridges. When you open it up and it cracks and the wad releases, you hear a little pop, and oxygen rushes into the bottle. Now, the thing is chemistry and the aging of wine is still somewhat of a mystery. I find this so awesome. I mean, it’s frustrating, but you cannot do a scientific experiment with a compromised subject. This means that the second you either penetrate a cork or open a bottle of wine or even put a syringe down into the cork, oxygen is affecting the wine. The only way to really know how wine ages is to age the wine. Isn’t that crazy?

There’s a debate about screw caps versus cork and how wines age. This is a discussion that’s going to be going on for quite some time, until somebody figures it out. According to the “Oxford Wine Companion,” science tends to lean towards the idea that wine is always in a reductive state because it needs the absence of oxygen to reduce — which basically means to evolve. Others believe the porous nature of the cork allows for tiny amounts of oxygen, which I mentioned before, to allow the minor oxidation of wine, and that ages the wine. Both of these things could be true.

Actually, if you take the thin tin foil layer out of a screw cap during production, that actually allows for gas exchange very similar to a cork. Now, what’s frustrating and beautiful about wine is we may not know for some years until we taste wines that have aged how they do compare them both. Either way, though, today the screw cap is the No. 1 alternative to the cork. It has a reliable seal. It has an inert substance. It’s easy to remove and insert. And it’s a pretty relatively low cost closure. Think of a cork as a dollar. A screw cap is 70 cents. The only big cost would be smaller wineries that don’t often have the ability to buy the components that add on to the bottling systems, and they have to pay. In the end, it’s less expensive. There are other corks out there, synthetic corks and plastic corks. There is something called agglomerated cork, which is a bunch of cork pieces and dust glued together that was invented in the United States. There are glass corks. Again, these are glass closures they actually have a little suction cup around them. They can be fragile and expensive.

Honestly, a screw cap is a way to go if you’re not doing cork. It was such a big deal. There is a pretty famous winemaker in the United States named Randall Grahm who has a winery called Bonny Doon. I don’t remember the year — maybe 1999 — but he actually had a funeral for the cork. He took his entire line of wines, got rid of the cork, and only uses, to this day, a screw cap. It was a big to-do. He did a funeral procession down 5th Avenue in Manhattan. It’s crazy.

I don’t know where everybody’s at with their mind and screw caps, but the thing to really know is that they both do the thing. Cork is a good closure. Screw caps are good closures. Scientifically and technologically, they’re great. The only thing is, cork has this thing called TCA that can form and just straight-up ruin a wine. The only way that a screw cap wine can be ruined is not with TCA, but if the bottling system is not sanitary. For example, if there’s anything on the lip of the glass bottle before the sleeve goes down, you’re compromising the wine, so it has to be very clean.

Today, there are screw caps that are used for sparkling wine. I’ve had them, and it’s awesome. It’s not necessarily for Champagne. I don’t know if it’s a pressure thing, but I’ve had Prosecco under the screw cap. It’s just cool. It doesn’t come down to which one is better than the other, like screw cap versus cork. Each one has its benefits. Some winemakers, like Randall Grahm, are just going all-in on the screw caps. Some winemakers use screw caps for their entry-level wines and reserve corks for their age-worthy wines. Some winemakers are aging wine under screw cap. Some winemakers are doing both.

These humans that make this stuff called wine every decade and every generation, something changes and they figure something else out. The screw cap is just one of them. I mean, the screw cap was meant for spirits and liqueur. Now, it’s the No. 1 closure for wine. It’s just part of the evolution of what we understand in wine. We’re just going to keep on evolving. We are going to keep on understanding, and it’s going to get better and better.

@VinePairKeith is my Insta. Rate and review this podcast wherever you get your podcast from. It really helps get the word out there. And now for some totally awesome credits.

“Wine 101” was produced, recorded, and edited by yours truly, Keith Beavers, at the VinePair headquarters in New York City. I want to give a big ol’ shout-out to co-founders Adam Teeter and Josh Malin for creating VinePair. And I mean, a big shout-out to Danielle Grinberg, the art director of VinePair, for creating the most awesome logo for this podcast. Also, Darbi Cicci for the theme song. Listen to this. And I want to thank the entire VinePair staff for helping me learn something new every day. See you next week.

Ed. note: This episode has been edited for length and clarity.