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In this episode of “Wine 101,” VinePair tastings director Keith Beavers discusses wine faults and their impacts on wine. Beavers explains the various things that can ruin a bottle of wine, including cork taint, oxidation, and spoilage yeasts — all of which affect the smell of wines. Cork taint, specifically, suppresses the fruit characteristics of a wine and makes it undrinkable.

Listeners will learn that excessive amounts of oxygen expose acetobacter, an acid bacteria that causes wine to exude a smell similar to vinegar. Beavers also discusses Brettanomyces, a fungus that is used intentionally in some beer styles but that is considered a spoilage yeast in wine.

Tune in to learn more about wine faults.

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Keith Beavers: My name is Keith Beavers, and I just got into NWSL. I found out there is a Gotham team for Jersey and New York. Let’s do this!

What’s going on, wine lovers? Welcome to episode 24 of VinePair’s “Wine 101” podcast. My name is Keith Beavers, and I am the tastings director of VinePair. How are you doing? Oh, by the way, it’s Season 2. The faults in our wines. How do we recognize them? What are they? Should we care? We just need the knowledge. Let’s talk about wine faults right now.

In the last episode, I got all poetic in the beginning about what you’re anticipating in a glass. We talked about vulnerability and how wine and grape juice has this vulnerability. We talked about how to protect that vulnerability. Just so you know, guys, I love this stuff. This is amazing because grape juice becoming wine is such an amazing, complicated, chemical enzymatic reaction party. In the best circumstances, all that nature and all that enzymatic stuff happens with a human coaxing it into existence. Then, you have something beautiful. Wine is so fascinating that way, but it’s also very vulnerable. There are all these things that winemakers have to combat to make sure that the wine is sound.

When things happen to wine that compromise the typicity of a wine — meaning where it’s grown, how it’s made, maybe in Europe, where the rules are in place to make it consistent — when these things happen to compromise, those are known as wine faults. I know the term wine fault is intense because the things that happen in wine that are nature’s “oopsies” can become something like the idea of noble rot or botrytis cinerea infecting a grape. People make very famous wines like Sauternes in Bordeaux. Out of that, people said, “Oh gosh, this is infected. Oh gosh, it makes great wine.”.

In Vinho Verde, the wine region in northern Portugal, Vinho Verde wine was often just very young wine. Before technology, the wine still had a little bit of yeast in them when they were bottled so there was a little bit of fizziness in the wines. These days, often Vinho Verdes are injected with CO2 to emulate that natural fizziness that happened back in the day. I guess the most famous oopsy of nature and humans interacting with this stuff would be sparkling wine. Oh my gosh, our bottles are exploding, but this tastes good. There are some things that nature throws at these winemakers that just cannot be or often have not been associated with being beneficial to the resulting wine. That’s where the whole wine fault thing comes into play.

If you’re buying a bottle of Pinot Noir, no matter where it’s from, you have an idea of what that Pinot Noir is going to taste like and what it’s going to smell like. Depends, but it’s a Pinot Noir. If something is considered a wine fault, it subtracts enough organic stuff so that when you smell that Pinot Noir, it doesn’t smell like a Pinot Noir. It’ll smell like something else. Vinegar, a mouse, a musty basement, or wet dog hair. There’s Pinot Noir somewhere in there, but these things take over, overwhelm the wine, and don’t allow your brain to enjoy the Pinot Noir stuff.

That’s just for smelling, enjoying aromas and flavors of wine but there’s also stuff you can see. It is not as intense as the stuff you can smell. That can really mess with the wine, your brain, and your enjoyment of wine. I’m going to go over a couple of things you can see, but I’m really going to concentrate on things you can smell. There are three things that happen to wine that will tell you something’s wrong when you’re smelling a wine. When you’re looking at a wine, a couple of things can look weird, but they’re not necessarily that weird. One thing is that sometimes wines, if they’re not cold- stabilized, there are things in the wine called tartrates. Those tartrates are soluble, meaning sometimes they can extract themselves from the liquid of the wine.

The wine is always aging. Wine is always reacting with itself. It’s always reducing itself inside that bottle so sometimes these tartrates become crystallized, and you’ll see at the bottom of a bottle, crystals. In white wine, they look like shards of glass or crystal. In red wines, they look like extremely brownish-dyed, red rocks, but they’re not. They’re just salts, and they’re not harmful at all. They’re just in the wine, and all they have to do is take them out and that’s something decanting can do for you. This doesn’t really happen much anymore, but sometimes a bottle can become cloudy. That’s just proteins that are coming out of the liquid as well. They eventually stabilize, and it’ll calm itself down. If you have ever seen the movie “Bottle Shock” with Alan Rickman, the late and great Alan Rickman, that is part of that movie.

Now, subtle bubbles in a young white wine from Vinho Verde in northern Portugal are very cool. However, sometimes you can get bubbles in an old red wine, which is not so cool, which means there was a messy bottling process and there was some residual yeast in the bottle. Over time, it slowly but surely ate that sugar and fermented a little bit in the bottle. It doesn’t increase the alcohol so much, but it creates carbon dioxide and few bubbles. In addition to that, it takes away a little bit from the fruit character of the wine.

Yet, it’s in what we smell that is really going to affect you as a wine lover. Looking forward to something and not getting it because nature did a thing, and there are three big things that nature does to wine to try to ruin it. There’s cork taint, oxidation, and spoilage yeast and bacteria. We’re going to wrap that into one thing. The first one, cork taint, is going to happen no matter what in the world, but the other two can be prevented by S02, which we’ll get into. However, cork taint is natural. It comes from a species of oak tree called Quercus suber. The tissue that is shaved off that tree is called lenticels. It’s very porous. That is what makes a cork for wine. That porous nature of the cork allows for gas exchange, which absolutely benefits wine, as you guys probably know.

Since cork is natural and porous, it’s always going to harbor fungi. It’s not dangerous to us, but it’s always going to be in there. Sometimes, during the sanitation process of corks, these fungi can produce what are called taint compounds. The most significant of these, and the one that messes with us the most, is a compound called 2,4,6-trichloroanisole, otherwise known as TCA, otherwise known as cork taint. From what I’ve read, there’s a theory that these compounds get their way into that little air space between a wine and a cork and then drop into the wine. This is crazy.

It takes only three to four nanograms per liter to mess an entire bottle of wine up. What happens is this taint compound suppresses fruit, not allowing our brains to recognize any fruit characteristics in a wine. You would sip it. You would get all the textural stuff that’s still there. But when you swallow the wine, there’s no finish. Jedi wine master Jancis Robinson has this crazy data saying that at any given time, 3 to 5 percent of the world’s wines are corked. I mean, that’s crazy, but here is the capper. This taint compound literally renders the wine pretty much undrinkable because there’s nothing there for your nose to enjoy, but it depends on your ability as a human to detect these things. And everybody is different. Everybody has what’s called a detection threshold. Everyone has a different detection threshold because we’re all humans and we’re all different.

In its most subtle form, it’s very hard to detect TCA because you’re still getting some fruit, but there is something wrong and it takes a minute to figure that out. You have to have had the wine the right way and then have the wine the wrong way to detect that cork taint. That’s why it’s so crazy. At its most extreme, there’s nothing going on in this wine and it’s just obvious something’s wrong. Now, often you’ll smell the moldy newspaper or wet dog hair but really what it is, is that there’s no fruit.

Even in our industry when we’re tasting wine, it’s always weird — who’s going to be the first person to say this wine is corked? I’m serious, and it is crazy. No one wants to be the first one to say it’s corked in case it’s not corked. That’s how subtle this stuff can be but the second you experience it, you’ll know it from then on, pretty much. As unfortunate as a corked bottle is, when I do wine classes IRL, I actually enjoy when a wine is corked so I can put the non-corked wine next to it so everyone can get a sense of what corked wine is and just get it over with. Real talk, this is one of the reasons why the screw cap is a thing.

Now, when we talk about opening a bottle of wine and we talk about decanting and wine in the glass, we always talk about how we want to encourage oxygen into the wines so it opens up and gives us all the things we want or what the wine wants to give us. Well, during the winemaking process, too much oxygen can be a bad thing. I know it sounds crazy. As we talked about in the last episode, oxygen doesn’t only give life to those browning agents, but it also gives life and feeds certain bacterias and spoilage yeasts that can produce other stuff to mess with the wine. During the last part of fermentation, when alcohol is being formed, part of that formation is a reduction of a certain compound called acetaldehyde, so acetaldehyde reduces into ethanol. I know this is a bit sciencey, but bear with me. It will all make sense, I promise.

What ethanol does is kill a lot of bacteria once it’s produced but there is a bacteria called acetobacter. It’s an acid bacteria that can hang out through this entire process. If too much oxygen is exposed to the wine, it can interact with acetobacter. What that will do is reverse the formation that just happened. It will convert ethanol back into acetaldehyde, which happens to be a main compound in vinegar. So you’re basically turning wine into vinegar. What that does is create a sour sensation, so you’ll be drinking a wine, and it won’t smell right. You’ll smell a little vinegar. If that ever happens, you know a wine has been oxidized, and of course, as we know from the previous episode, a way to prevent this from happening is to add a little bit of S02 to kill those browning agents and render them impotent so this doesn’t happen.

There is a species in the yeast genera named Brettanomyces. This is not the Saccharomyces cerevisiae we’re familiar with, which converts sugar into ethanol and carbon dioxide to make wine. This is a different yeast. Of the five or so species of this particular yeast is one called Brettanomyces bruxellensis, which was named after the Senne Valley just outside of Brussels in Belgium. It is a very, very important and essential yeast strain or species for lambic beers and gose beers that are so famous in that part of the country. For beer, it actually is beneficial, but this yeast is also found throughout the wine world. In the wine world, it’s not beneficial.

The wine world considers the Brettanomyces yeast a spoilage yeast. OK, bear with me here because this is really awesome to understand. In a normal winemaking situation, Saccharomyces cerevisiae eats the sugar, converts it to alcohol and carbon dioxide. This is fermentation. Wine is being made, and as we talked about in the first season, as the alcohol gets to a certain point, it renders the yeast impotent. The yeast dies, and then we have new wine. Then, the process continues. Now, what we have here is a wine with residual sugar and depth and all the things that are going to happen after we’ve gone through the entire winemaking process. If Brettanomyces is in that must and it is in that fermentation process, once Saccharomyces cerevisiae — the beneficial yeast for wine — is rendered impotent and dies, Brettanomyces is still around. The winemaker knows that when the yeast dies, that’s the residual sugar. That’s the depth. That’s the wine they want.

However, Brettanomyces goes in and starts eating the residual sugar and converting it. What’s crazy is that Brettanomyces is anaerobic and aerobic. It doesn’t matter if there is oxygen or there’s no oxygen, it’s going to do its thing. If it’s there, it’s doing work. Instead of ethanol and carbon dioxide, what Brettanomyces produces are two compounds that can affect the aroma of a wine. It produces a lot of compounds, but two are really significant. It produces something called 4-Ethylphenol, or 4-EP. It also produces 4-Ethylguaiacol, or 4-EG. Again, it is a lot of science, but bear with me. This makes sense.

The 4-EP compound will introduce to the wine an animal or medicinal smell. Some people say sweaty saddle, not very attractive. Actually, this is the compound that diagnostic laboratories used to prove that a wine has been infected with brett. The other compound, 4-EG, has smokiness. This compound brings some smokiness and some spiciness. Some people say it smells like cloves, but it brings a dark, mocha spiciness to a wine. Now, some people believe that in small amounts, and I have smelled this in small amounts, the smokiness adds a little bit to the complexity of a wine, even though it’s a little bit out of place. If it gets out of hand, it’s all you smell. If the population is really large and it’s getting a lot of oxygen, it forms compounds called tetrahydropyrimidines.

If you’ve heard at all about wine smelling mouse-y, this is the compound. When this compound gets into wine, a mouse is out and you can’t smell anything but mouse, mocha, smoke, and maybe some medicinal stuff. Not only has the Brettanomyces eaten a lot of the residual sugar, but it has also produced these other things that mess with the wine’s complexity. Anyway, I know this is crazy science stuff and it’s intense. It gets even more so if a barrel is infected with a Brettanomyces population, it’s there forever. You actually have to get rid of your barrel. These are things that can be prevented by S02 and cleanliness.

Hygiene is a big deal with wine. The wineries are clean, and they try to make sure that these yeasts don’t get in to spoil the wine. Now, there are some winemakers out there — I don’t know if they encourage oxygen, Brettanomyces, and these things into the wine, but they believe that these things can add complexity to wine, so you’re probably going to encounter some of these wines at some point.

These wine faults, spoilage yeasts, oxidation, or things that can be preventable but sometimes allowed, it doesn’t matter where it’s made, it’s always going to smell the same. It’s going to smell like ethylphenol or it’s gonna smell like ethylguaiacol or tetrahydropyrimidines. It’s going to smell medicinal, mousey, and smoky. All those things are going to mask what the wine initially was going to be. When you’re smelling these wines deep down in there, under all the weird smoke and other stuff, there’s a wine under there. But unfortunately, you’ll never really get to it. When these compounds overwhelm a wine, they overwhelm your threshold of perception. You tend to really just smell all those things. You never really get to the real fruit of the wine because a lot of the fruit is gone and there are a lot of compounds overriding what was left.

There you have it, guys. These are some things that you will encounter IRL out there enjoying wine, and here’s a way now that you can catch them. There are certain wines where some of the stuff is done intentionally, and you’ll come across those wines. Then, you can decide whether they’re your jam or not. Now you know, and you have all the information you need to know to make your own decisions.

@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.