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In this episode of “Wine 101,” VinePair tastings director Keith Beavers discusses cooperage, the art of barrel-making. Beavers details the history of barrel-making, which dates back to the Iron Age. He then explains the complex process that goes into barrel-making, which involves cutting down trees into staves and using different combinations of wood to create the final product.

Listeners will also learn about the importance of duration and temperature control when it comes to barrel-making as well as the science behind barrel maturation, in which wine evolves and develops oak flavors during barrel aging.

Tune in to learn more about cooperage.

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Keith Beavers: My name is Keith Beavers, and if you think I love “Star Wars,” wait until “The Wheel of Time” comes out. Light. It’s going to be amazing!

What’s going on, wine lovers? Welcome to Episode 25 of VinePair’s “Wine 101” podcast, just chilling out in Season 2. My name is Keith Beavers. I am the tastings director of VinePair. How are you doing?

Guys, this stuff is complicated. Cooperage. What does it even mean? It has to do with barrels, but it’s more than that. We’re talking about barrels in general, how wine and barrels get along, and how trees become barrels. Let’s get into it.

I know I say this a lot because this podcast is bite-size info for you guys to take with you and help you on your wine journey. Yet, this subject here could not only be a series on its own but could be its own podcast. OK, that’s too much. This subject we’re about to talk about is really in-depth, complex, mysterious, and old. There’s so much of it to talk about, and I can’t fit it all into this episode, so I’m going to go through this subject called cooperage. I’ve selected some things I think that you need to understand to get a good sense of it. Then, at any point in the future, we can go more into it.

I don’t know if this is a good or bad thing, but throughout my wine career, I didn’t take barrels for granted, but I just thought, “There’s a barrel. That’s what happens. You put the wine in the barrel, and then it does its thing.” However, you learn about what barrels do with wine and how it interacts. It’s really cool and we are going to get into that, but it’s not until I went to an actual cooperage, in France, that I saw how crazy, intense, complicated, and in-depth this industry is. It is also mysterious. I went to a cooperage somewhere in France, I can’t remember where it was. I was not allowed to take pictures because the way that this company makes their barrels is a secret within that family.

This is a common thing in cooperages or the more artisan barrel-making world of France. Today, the art of barrel-making or cooperage has definitely advanced and there’s some technology involved, but the word cooperage is an all-encompassing noun for all wooden containers. Cooperage is also a word used for the business of making those containers. A “cooper” is someone who actually does the work to make the cooperage happen. It is a little bit confusing but I think we got it.

Even though we do have some modern technology to help us make barrels, the idea of the barrel to store things in has been around for a very long time. What’s very hard about wood and wooden barrels is that they deteriorate over time, more so than amphorae. It’s very hard to track the history of barrels and the movement of barrels through trade because they’re gone. Yet, through documented evidence or history, not physical history, barrels have been made all the way back to the Iron Age. There’s evidence that the Celts were using barrels for large-scale transportation. There’s mention that Julius Caesar in his campaigns in France encountered barrels during the ‘50s B.C.

Towards the end of the first century, Pliny was describing the barrel to his Roman audience, knowing they had no idea what that meant. He apparently had discovered them in Gaul, and it’s in the 3rd century we start seeing barrels showing up in literature and art. What is fascinating when I was reading about this is that after this point in history, you can actually track the decrease of use of amphorae. Even though we don’t see the barrels because they’re gone, it’s cool how you can track it through the decrease of the use of something else. That’s wild stuff. I don’t want to spend too much time on the history of the barrel because we all know what a barrel looks like. For our purposes, I want you guys to really understand how wine and oak interact with each other. I think that’s really fascinating stuff and you can apply that knowledge when you’re actually drinking wine.

There’s really no evidence of how wine in barrels became a thing, but what people talk a lot about in the industry are the stories of trade. At some point, someone made a wine and put it into a barrel. It got on a ship and made it somewhere else. When it was in its original location, it tasted one way. When it got to its other location, it tasted different but better. This was a gradual realization. Then, at some point, wine in barrels became part of our industry. Obviously, this all started because barrels throughout history were used to store all kinds of goods and they are designed specifically for transportation. The way a barrel looks, which has a bulge in the middle, allows it to be put on its side, spun, and rolled onto a ship and off of a ship. Before the advancement of steel and plastic, you can imagine how important these barrels were. Of course, as those things became more prominent, the wooden barrel became less so.

Today, the wooden barrel is mainly for wine, spirits, and beer. But it’s so important for the drinking industry that this old, artisan-style trade of cooperage is still around. You see it mostly in France. You don’t see it as much in the New World like the United States, which is a big oak producer as well.

This process involves cutting down trees that are at least 100 years old, cutting them against the grain into staves, and then leaving these staves out in nature for up to 36 months — only to be taken in, heated, shaped, toasted, and turned into a barrel. It’s a lot harder than that. Every species of tree is different. Every tree within those species is individual and unique, and there are different combinations of woods that are used. Mostly it’s French oak and American oak, but there’s also been chestnut, cherry wood. There are barrels that are a combination of woods, a combination of forest, a combination of trees, a combination of staves. It’s all very different.

There are also different ways to cut the staves, whether using French oak or American oak. There are angles you have to cut to make sure that when you put the staves together that they are airtight. Depending on all of that, that I just said, you have to toast the barrel. There are three general types of toasting for the barrel, basically firing the inside of the barrel to solidify the protective layer between the wood and whatever you’re putting in the barrel. Then, you have to think about what wood you’re using and how much you want the barrel to be toasted based on the reactions from fire in the wood. It’s an absolutely complex, almost thinking-ahead-of-the-game industry.

There are some winemakers that actually go out to the forest and select trees, knowing they’re not going to get that tree made into the barrels for well over maybe three or four years. The thing that winemakers have to think about when selecting a barrel is they come in different sizes. What size do you want? And each size has a different result for the wine. How old do you want the barrel to be? You can get a brand new barrel. You can get barrels that have been used a few times, and those affect the wine. What type of wood do you want the barrel to be? That will also affect the resulting wine. How is that barrel made? Is it a cooperage that you like? Do you need to get a barrel that’s based on your specific winemaking techniques, your specific region? Are there laws in place for wine to be a certain way so these barrels are the ones that you use because you want to be within these laws? How much time is this wine going to be in the barrel? If so, how do you predict the wine will be after the barrel has been in for that long?

You have data. Everyone has data, I’m sure, but every barrel is different. Last but not least, the big one was how much toast do you want in your barrel? How much time do you want fire licking the inside of the walls of that barrel? Different levels of toasting will affect the wine. That’s a lot of decisions to make. Fundamentally, how cool is it that the wine world has all these happy accidents, and the barrel is one of them? It just so happens that this thing, naturally made to store food and stuff, just so happens that the way it’s created and what it’s created from benefits wine tremendously. Wow, pretty amazing!

When we put wine into a barrel and let it sit there and interact with what’s inside, we call that barrel maturation. Of course, Jedi wine master Jancis Robinson puts it so nicely. Barrel maturation is the winemaking operation of storing a fermented wine in wooden barrels to create ideal conditions for the components of the wine to evolve and that the wood imparts some oak flavor. Really, there are two parts here: evolution and extraction. The way a barrel is made with small amounts of air being able to get into the barrel is what helps the evolution and the maturation of the wine. And the char and the actual constituents in the wood inside the barrel interacting with the wine is what adds flavor. For me, this is the fun stuff. This is a wine truly becoming a wine if it’s meant to be made in this way, of course.

If a winemaker is using wooden barrels to rack wine, that means that wine is seeing some oxygen. The benefit of having a barrel to rack from is that it clarifies the wine, meaning all the sediment initial from the fermentation falls to the bottom of the barrel, but it falls in one spot. It all convenes down in that little bottom part. It’s easier for the wine to be racked off of a wooden barrel because all the sediment falls into one place.

The barrels are being filled and emptied through racking through a hole in the side of the barrel that is stoppered by a plastic wad called a bung. After the racking is done and the wine is ready to mature in the barrel and the bung has been put into the hole, the barrel is then rolled into a rack. Through this entire process, there have been small doses of oxygen soaking into the wine. These are very small, yet very significant and very important saturations that will help the wine mature.

As the wine interacts with the oxygen — whether slow or fast, however the winemaker wants it to happen — those primary aromas we talked about all the way in the first season begin to reduce. Oxygen also causes small tannin molecules to gather or attract each other, what’s called agglomerating. These little tannin molecules agglomerate, and they reduce a little bit of the color of a white wine, turning it more towards gold. In red wine, it starts softening the astringency of the wine, softening the tannins. Some of these tannins start to absorb the anthocyanins in the wine. Again, that’s the color pigments that are natural in the grape we talked about in the first season. These tannins soaked in pigment are called pigmented tannins, obviously. Once they’re pigmented, these tannins are much more permanent in the wine than the natural anthocyanins. This goes into how the wine ages and loses color over time.

Well, the pigmented tannins will hold on longer than the anthocyanins. When you see a red wine starting to age and lose color, it’s the natural anthocyanins that are leaving and not the pigmented tannins. I know it’s crazy, but it’s so cool. Sorry, I love this stuff!

Now, as the wine interacts with the actual wood, alcohol is working to soak its way slowly but surely and steadily into the wood. There is a protective layer between the wine and the wood called the toasting. We’re getting to that in a second, but there are things in the wood that extract into the wine that help give the wine certain characteristics. The alcohol assists in that extraction.

One of those extractions is a compound called lactones. It’s derived from these macro-biomolecules called lipids that are soluble. The levels of these lactones depend on the kind of tree, the tree itself, and parts of the tree. Yet, at very high levels of lactones in the wine, when you smell coconut on a wine, that’s what this is. American oak has naturally high levels of lactones, more so than French oak. No matter the oak, toasting a barrel and toasting wood can actually increase the levels of lactones available. I’m talking about French oak and American oak primarily, but there are other woods that are used to age wine, but these are so more popular that I’m going to stick with these two. Of course, that vanilla thing happens a lot with wines that see oak.

The thing is, it’s vanilla. OK, so it’s not the vanilla bean. It’s actually a phenolic aldehyde called vanillin, and it’s found in the vanilla bean, but it’s also in oak! It’s a product of what’s called a lignin. The lignin in plants is, bear with me here, a complex organic polymer. I know it sounds crazy. All it means is a repeated organic pattern. It’s what makes plants woody or rigid. As the lignin breaks down in the wood, the alcohol extracts the vanillin into the wine. Again, toasting will increase this, but also the seasoning of staves out in the air also concentrates the vanillin.

As the lignin further breaks down, this is where the really cool stuff starts to happen. The smoky stuff, the spicy stuff. These are called volatile phenols, and they extract into the wine as the alcohol penetrates the wood. These phenols are harder to coax out. Actually, seasoning staves in air decreases these phenols. When a wine has these characteristics, you know that it has taken some time in the barrel to develop compounds like eugenol, which gives this clove-like aroma. guaiacol and 4-methyl guaiacol give that smoky, charred aromas. You’ll recognize guaiacol from the Brettanomyces episode but this is methyl guaiacol, not ethylguaiacol. There’s also something called 4-vinyl guaiacol which gives you this nice carnation note so the floral notes you get in red wine, that’s it.

I’m giving you all these names and all this stuff because when you smell wine, this is the complexity you’re smelling. To top it all off, as carbohydrates degrade into the wine, they form products as well to add to the aroma of wine, things like furfurals. This is the compound that gives you that coffee note or cooked bread note. Maltal and cyclotin are the two things that give you that multi-caramel note in wine. Last but not least, tannin. As the lignin breaks down even more, it extracts tannin into the wine. This adds tannin into the wine and adds structure to the wine. This is crazy nature stuff, doing wonderful things. Over time, humans have tried to control this but manage it so that you get something beautiful out of it. Can you imagine if something like Brettanomyces got in there, infected the barrel, and started eating all of this natural sugar, degrading the complexity of what this wine wants to do? Huh, nuts.

Now, all this and more happens in a barrel. A lot of this interaction is defined by how much that barrel is toasted. Is it a light toast, is it a medium toast, or is it a heavy toast? As I said before, the toast is this protective barrier between the wine in the wood. It’s not that we don’t want the wine to interact with the wood. It’s almost like a delayed reaction depending on what wine you want to make. The less toasting of the wine, you would get more of the tannin and other characteristics leached into the wine. In a lightly toasted barrel, the wine is going to be more oaky and woody. It’s still going to have some fruit to it, but it’s still going to be tannic.

This is a barrel that’s been toasted about up to 356 degrees Fahrenheit for about five minutes. That’s a light toast, and the wood is still going to be a little bit light. If you increase it to almost 400 degrees F and toasted for an extra five minutes for a 10-minute toast, this is where the vanillin comes out and the coffee notes. This is where wines are a little bit less tannic because it takes longer for the wine to interact with the tannin in the wood. These wines can be rounder or smoother, but they still have tannin and they’re still what’s called “persistent.” Of course, the wood is getting browner. Now, if you go for 15 minutes at well over almost 450 degrees F, that’s called a heavy toast. The wood is dark. This is roasted beans. This is where you get that toasted bread and cloves. Some people get nutmeg on this stuff. It’s like smoked meat. Sometimes I call it spiced meat, but it’s really smoked meat.

Those are just some things that happen in a barrel when a wine is interacting with the wood. All these aromas we talked about in the first season, all those things you’re trying to get in your head, these things are just some of the more apparent stuff. All the other wacky stuff that comes into your brain from stuff you’ve experienced in your life that comes out of wine, that’s just your perception of it all. The beauty of wine is that you get to perceive it however you want.

However, here we have actual, natural compounds being leached into a wine. One of them is called vanillin, and it’s actually in another plant called a vanilla bean, and you actually can smell it. This is just amazing stuff and this is how complex wine is. Once you make the wine, you put it in a barrel, and you have to wait for nature to do its thing. This is a natural way of wine evolving. This is why some places in Europe have laws in place for how long a wine needs to be in a barrel before it’s put into a bottle. Even when a wine is in a bottle, there are laws about how long it needs to stay in the bottle before it’s released. A lot of this is because of the interactions with wine and wood and how long or short that region or winemaker needs for that wine to achieve the complexity level at which they believe, or the region believes through consortiums and laws, that a wine is ready to be released.

This is why winemakers add SO2 to wines. This is why winemakers try to keep spoilage yeasts away from wines, because these natural complexes are so subtle yet so beautiful. These things can compromise not only your experience but what the winemaker wants to show you. A little bit of Brettanomyces here and there is not bad for a wine because it can add a little bit of smokiness to it, but there are other constituents in barrels that can add smokiness to wine.

Nature is just crazy, guys, but there you have it. I hope this helps you understand cooperage, barrels, what goes on in this world, and how it applies to wine. Next time you’re drinking a wine that has some oak on it, you can get an idea of how it all got there. See you next week.

@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.