“When smoke impact in the vineyard is great enough to impact the fruit and causes inferior wine, then we start calling it smoke taint.” explains Anita Oberholster, Professor Cooperative Extension Enology in the Department of Viticulture and Enology at the University of California, Davis. During a wildfire event, the lignin in vegetation is broken down, releasing volatile phenols. While there are naturally occurring phenols in grapes, this release causes an excess which can impact the final product. Some tainted wines smell like camp fire, smoky, BBQ, and even bacon. New research shows there is an aftertaste, an aroma you perceive in the back of your throat, that creates that ash tray character. Fruity aromas natural to some varieties can mask smoky aromas quite well. While green aromas like green pepper bring out the undesirable smoky traits. Some varieties may stand up to smoke taint better than others but there has not been a definitive research project on this yet due to the complexity of the testing process. Barrier spray research is still in its infancy. Early testing shows that barrier sprays need to be used preventatively. One trial showed a slight impact that could make a positive difference in a light smoke taint situation. The additional challenge with sprays is that they need to be washed off which uses a lot of water. Listen in for Anita's number one tip for growers. References: Anita Oberholster, UC Davis Viticulture and Enology Webpage Key Information on Smoke Effect in Grapes and Wine: What can be done to identify and reduce smoke effect in grape and wine production? (Western Australia Agriculture Authority) Grower-Winery Contracts and Communications about Smoke Exposure to Oregon's 2020 Wine Grape Harvest SIP Certified Step-by-Step: How to do small scale fermentations Sustainable Ag Expo November 14-16, 2022 | Use code PODCAST for $50 off The Australian Research Institute Smoke Taint Resources Get More Subscribe wherever you listen so you never miss an episode on the latest science and research with the Sustainable Winegrowing Podcast. Since 1994, Vineyard Team has been your resource for workshops and field demonstrations, research, and events dedicated to the stewardship of our natural resources. Learn more at www.vineyardteam.org. Transcript Craig Macmillan 0:00 And with me today is Dr. Anita Oberholster . She is Professor of Cooperative Extension, enology in the department of Viticulture and Enology, UC Davis. And today we're gonna talk about smoke taint. Welcome to the show. Anita Oberholster 0:11 Thank you. Thank you for having me. Craig Macmillan 0:13 This is a problem that has gotten a lot of attention in the last few years in California, I think a lot of us was surprised to find out it's been a topic of conversation in Australia for much longer than that. And yet, we still have a lot of questions. And we still don't have a lot of answers. But we're making progress. We're learning more about this. So first off, can you define what smoke taint is? Anita Oberholster 0:35 Sure. So the first thing I would want to say is that, you know, when a vineyard is exposed to smoke, we talk about smoke impact, this potential smoke impact. Smoke taint is actually a sensory term. So that is when you have something that causes a decrease in quality or fault in the wine, then we start calling it taint. So when smoke impact in the vineyard is great enough that it impacts the fruit in such a way that it makes wine that is inferior and has a fault, then it is smoke taint. So smoke impact in grapes causes potentially smoked taint in wine. That clear? Craig Macmillan 1:16 Absolutely. So there would be smoke impact then, as a standalone, what would be smoke impact? Anita Oberholster 1:21 Okay, so smoke impact would be that there was fresh enough smoke that the grapevines were exposed to that the grapes absorb some of the volatile phenols coming from the smoke, so that it's more than normal. So smoke impact would be there were some absorption that took place. So grape composition is not totally what it was before smoke exposure, that would be smoke impact. Craig Macmillan 1:47 And then smoke taint is what happens when you turn it into wine. The aromas that you get from that? Anita Oberholster 1:51 Yes, and if the smoke impact was enough, because if you only have a little bit of absorption, that may still be a result in a wine that has no problems, right. So the smoke impact has to be at a certain significant level before we see a problem in the wines. So it's very important to know just a little bit of absorption do not always equal a problem in the winery. Craig Macmillan 2:16 What kinds of aromas in terms of like descriptors and also then what kind of compounds, their aromas are compounds, what kind of compounds are we talking about? Anita Oberholster 2:27 Okay, so I'm gonna get a little bit scientific. Craig Macmillan 2:29 Do it please. Anita Oberholster 2:30 So if you think of smoke, right, if we think a wildfire smoke, you have a lot of vegetation burning . So 15 to 25% of wood is lignin now lignin is what give celery its crunch, okay, so it's what it's the fiber you food. It's what gives wood its structure, its hardiness. When lignin burns, it actually release a lot of compounds. When it breaks down, we call thermal degradation. It releases a lot of compounds that we call volatile phenols. It's a whole range of compounds. And these compounds are naturally present in grapes. So that is something to remember, naturally, in different grape varieties in different regions would have natural, a certain amount. Now you have an excess amount in the air that can absorb onto those grapes because grapes are little little sponges, that absorbs the extra volatile phenols. Now if you have an excessive amount of volatile phenols, then it can result in wines with off flavors. Now what we talk about here is on the nose, you can get very campfire, smoky, BBQ, bacon, medicinal and the list goes on, aromas, but what for me is very distinctive, I call smoke taint, we call it a ritrum nasal character, or people talk about an aftertaste, it's actually an aroma you perceive in the back of your throat because what happens when these volatile phenols absorbed onto grapes, part of their defense mechanism is they attach sugars to it so as soon as you add sugars to it, this moment of fear now there was a really small compounds that's volatile and you can smell becomes non volatile because it is now larger in weight. But when you make wines both the free and without, so both of those with sugars on and those who have no sugars on, gets released into the wine. That rates your changes within the enzamatic activity, the pH of wine. And when you taste a wine, you have enzymes in your saliva that can actually release that bound. And we think it's that action that gives you that ashy character in the back of your throat. So it's a ritual nasal character because the back of your nose is connected to your throat as we all know when you have a cold and basically that release makes you perceive it and it's like an ashtray character if you can imagine an old campfire in the morning but that smells like if you licked that what that would taste like or if you smoking you have the old ashes there. I mean, I used to as a kid, my dad used to smoke a pipe, put the old coal pipe in your mouth and suck on it, that kind of taste. So obviously, that's very awful. So that would not be something that will increase the quality of your wine. So that for me is smoke taint. I have to caution that if you smell like, you know, smoke or something in wine, and only that, that doesn't always mean smoke taint. And there's other things that can happen in the wine that could also give you those characters. And you know, even barrel aging, some barrels can give you smoky character. So I want to caution people not to smell smoke and go oh, this is what tainted. Really focus on is there that aftertaste character that ritrum nasal, ashy character that's really distinctive. Craig Macmillan 5:48 Are there particular compounds that are kind of hallmarks that either are the most commonly found in wines that are identified as having ssmoke taint from a descriptor standpoint. Or ones that just tend to travel with those descriptors, even if they're not the compound itself? You know, what I'm talking about, like a proxy? What are those? And where did it come from? Anita Oberholster 6:05 Yeah, so we do have, you know, and we can thank our Australian researchers for that, because they've been working on this for much longer. And they have found about seven key volatile phenols, I can list them guaiacol, 4-methylguaiacol, syringol, 4-methylsyringol, p-cresol, o-cresol and m-cresol. they have identified six individual bound compounds that also correlate with smoke. So they've actually isolated them looked at them showed that they correlate with smoky characters, and the distinctive smoke taint character in wine. However, research continues. Even analyzing all those compounds, does not give you 100% predictive power, it's only about 70%. So we do think that there are more compounds that we need to keep on looking for. And that's something we're actively researching, but also the matrix. So the matrix is everything but what you're talking about. So for wine, it would be everything but the volatile phenols. We know that how much phenolic or color, polysaccharides, proteins, alcohol, sugar is in that wine, all of that influence the perception of smoke. So that can also be why the predictive power isn't that great. It could be everything else, not just the mark compounds. For instance, we know like fruity aromas can mask the smokiness quite well. But green characters like you know, the green pepper character or grassy characters, they actually uplift, smokiness, that's from research coming from South Africa. Very complex, everything in the wine influences something else. Craig Macmillan 7:41 You know, that actually just remind me of another another question. Do we know? Are there certain varieties that seem to be much more prone to either suffering from smoke impact or if they do suffer from smoke impact, having being identified as having smoke taint later on down the line? Anita Oberholster 7:57 Yes, you know, it's it's difficult. We really need more data. We we know, a variety like Pinot Noir, for instance, seems to be pretty prone to showing smoke. But is that because they absorb more? Is it something to do with the skin structure? Or is it just because they many times make wines where most simpler matrix is then, for instance, a full bodied Cabernet Sauvignon? And it's really difficult to know, we know that, for instance, Syrah naturally have very high levels of volatile phenols and can handle additional volatile phenols come from smoke quite well. That doesn't mean you can't get smoke impacted Syrahs. I've seen them. But so Syrah seems to be more robust. It seems to ask you know, Pinot Noir definitely more sensitive, say then Cabernet Sauvignon. Cabernet, Merlot, Cabernet Franc, Petit Verdot. I think the Petite Verdot perhaps a little bit more sensitive to the Cabernet Sauvignon but this is more based on anecdotal experience, rather than having enough research data to really piece it out. For us to really determine this, we would have to intentionally smoke different varieties so that they actually at the same ripeness point gets exposed to exactly the same volatile phenol compositions and smoke composition, and then evaluate them. As you can imagine, that's not easy to do. Craig Macmillan 9:20 No, it's not. Maybe I'm misremembering this, but I think I read an article where researchers were tenting rows of vines, and then building fires at one end and then blowing the smoke into the tent. And I was like, that's genius. But then in the, in the conclusions, right, the discussion, limitation, it's like, yes, but did we use the right wood? Is the intensity right? Is this over top, you know, you know, all these other variables and you're like, oh, God, you know, holy crap, what are we going to do? You know. And a lot of it's going to end up being what work that you guys are doing, which is just real in the field research when things happen, you just go study it as best you can. Yeah, you know, so it's gonna be a long time for us to figure a lot of these things out. Anita Oberholster 10:03 Yeah, we do a combination of it. But it's not easy. We've done some intentional smoking last year. And you know, we built a tank, it was like 36 feet by seven feet by 10 feet to cover for vines in our Vineyard. Just to test barior sprays, right. And then to figure out what to burn, we had some natural ash that we analyze. So Tom Collins in Washington State University, he used to burn natural vegetation and gave up because to keep it consistently the same, to know that everything was exposed to exactly the same smoke. It's difficult. So we've moved to like using pellets, but then not all pellets give up the same depending on what what they're made of, and usually hard work. And what we usually burns here in California is soft wood. So yeah, it's tricky. We had to play around with a lot of different fires to figure out which source material we should be using for for our intentional smoking. And we will keep investigating, we're trying to mimic the real situation as much as possible, but it's not perfect. Craig Macmillan 11:06 What is the window, or the progression of the windows for smoke impact on grapes when they're most vulnerable? Anita Oberholster 11:13 Yeah, you know, unfortunately, I have to tell you, basically, from the moment you have a berry,. There was this research in Australia on Merlot vines where they actually intentionally spoke, expost ir to smoke over three seasons at different growth stages. And they did find in that study, the most sensitive was from verasion on onwards. So from sugar accumulation onwards, right, our color change onwards. However, we've had many instances of now our vineyards that were only exposed to smoke before veraion. At pea size even and still ended up making smoke impacted wines. So I want to caution I would say the risk gets higher from verasion onwards. But unfortunately, you're not safe if your smoke exposure was earlier. Craig Macmillan 12:04 So it's an issue no matter what, basically. Anita Oberholster 12:07 Yes, unfortunately. Craig Macmillan 12:08 That's unfortunately, but also, that's good to know, that's really, really good to know, because I think we're thinking, oh, you know, it's a tiny berry and its all waxy and you know, it's not going to be an issue. And then, you know, four months later, three months later, suddenly, it's a problem. Anita Oberholster 12:20 I also heard this rumor of my grapes are fine, because they were overripe with smoke exposure. Now, unfortunately, that does not work either. It will absorb smoke, even if it's very ripe. The enzyme activity within the berry do decrease somewhat. So there might be a difference in how much they actually attach sugars to it, or, like these volatile phenols. But they're still sensitive, you still have a risk, there's unfortunately no period that you don't have a risk if you have a berry on the vine. Craig Macmillan 12:50 Got it. Oh, related. This reminds me of something. So the volatile phenols that we're talking about. These are compounds that are out in the air. They're part of smoking in quotes, but they're not ash. Ash is something's completely different, right? Anita Oberholster 13:05 Yeah. So ash is carbon, mostly right? So what can happen and this is the confusing thing. When you have a fire ,volatile phenols are very small, you can't see them, right. So what you see is the debris or the particulate matter, volatile phenols on their own actually break down very quickly, they phyto oxidize in the air within hours. But now they can absorb on to particulate matter. So they can absorb onto the ash. And when they absorb onto the ash, we do not know how that impacts their degradation. So there's where the issue comes. So and this is why we say only when smoke is fresh, is there any kind of relation between particulate matter and risk of smoke exposure. The older that ash gets, the older that smoke gets, the less it contains volatile phenol, phenols. And the lower your risk of smoke impact, if that makes sense. Craig Macmillan 14:02 I was just going to ask you about that. You've mentioned freshness in some of your other work. How fresh is fresh and how does it change over time? And is there any way I can sleep at night thinking that this has been out there for three days or whatever? Anita Oberholster 14:14 Yeah, you know, it's difficult, So basically at the moment, fresh ash is defined as anything less than 24 hours old. Now that's based on anecdotal data. The Australians had a fire, all the smoke moved in a column over the ocean and came back as one big column over McLaren Vale. And it was more than 24 hours later, and McLaren Vale was fine, there was no impact. So that was all anecdotal, but my own observations really do confirm that. I'm not saying you have no risk if the smoke is older than 24 hours, but your risk definitely substantially decrease. The older that smoke gets. Because what happens the volatile phenols starts breaking down, even those absorbed onto particulate matter starts breaking down. So after you know two, three days eyes that smoke is particulate matter. It doesn't contain the compounds that can absorb onto the grapes and into the graves and cause a problem. Craig Macmillan 15:10 We've talked about time, in fact about windkow. Let's pretend Craig's a grower, I was at once but I am not now. What can I do? What should I do? What should I not? Do I have any kind of agency in this process? Anita Oberholster 15:21 I wish I could tell grapegrowers what to do. I have some cautionary tales. If I can put it that way. Please, please. So what I would say is currently, we do not recommend anything. We've looked at some berry sprays, things they can spray onto the berry to protect it against the volatile phenols in the air. We've tried kaolin or surround, you know, the claim. Yep, yep. And it has shown some efficacy. So if you want to spray that on, you can try it. But it's not a silver bullet. In laboratory conditions. This is now 100% coverage, I saw about a 30% decrease in the amount of volatile phenols absorbing from smoke. But now remember, in a vineyard setting, you're not going to get 100% coverage, you may get 30 to 40% coverage. But it's a fact where if you only have a little bit of smoke exposure, that every little bit of prevention could actually mean the difference so that you end up with grapes that's not impacted and make good wine. This is always going to be preventative. Growers might have heard of the study that you looked at Praka, and it showed really, really good efficacy. However, after that initial study, there's been two more studies that showed no efficacy, and some that actually showed it resulted in the absorption of more of volatile phenols. So I'm cautioning against using Praka. I've looked at EMP barrier, I've only done one study 100% coverage. So keep that in mind. And one of their compilations, jin3e showed something very similar to surround not better. But in a similar similar realm. Here's the problem with whatever you put on, you need to wash it off. At this stage, it seems the volatile phenols absorbs onto the barrier instead of absorbing onto the berry. However, if that barrier is still there, when you pick the grapes and make the wine, it dissolves from the barrier into your wine, so you're no better off, you still have to wash it off. And that's the problem because removing that clay from the berries, that's very difficult and will need a lot of water, which is my other problem with the solution. We are continually looking at other barrier sprays, if we can find something that potential you don't have to rinse off. Because that would obviously logistically and for many other reasons be a better option. There's something else I would like to say. Some of these studies looked at compounds I just mentioned, like Praka in some of the studies and actually made it worse. We are concerned a lot of applications use the stickers, many times it's oil to get the compact stick to the berry. If there's too much oil in whatever you are applying, it seems like it doesn't dry out. And if you have something wet on the outside of the barrier that increases the volume of the berry, or potentially is a liquid and the outside of which the volatile phenols can absorb and then absorb for concentrate in that liquid and then go into the berry. That may be why in some circumstances, some compounds are making it worse. Some berry sprays are making it worse. We saw people applying fungusicides and things like that that also made absorption worse. So currently, really if there's smoke in the air, and you do not have to apply something to your grapes, don't. We're really worried about applying anything while there's smoke in the air. If you want to apply something as a protection, the only things that showed some efficacy is basically surround or potentially some of these EMP various sprays you have to do it preventative, you need to do it before there's any smoke. So you're going to do this not knowing whether you actually need this protection or not. When the smoke is there, it's too late. Please do not apply anything to you grapes, your vines while there's smoke in the air. Wait until the smoke clears. If you do have to apply fungicides and other things. That's important. The other thing also there's been some studies looking at leaf removal or not leaf removal. Now the thing is the volatile phenols can also absorb onto leaves. And actually when you have a big canopy, that canopy can actually sort of protect your grapes because the volatile phenols is absorbing onto the leaves, not onto your grape bunches. Craig Macmillan 19:40 We don't believe or we don't know at this point or we don't believe that those things aren't going to be transported from a mature lead back to the berries just like I'm transporting all these other precursors and amino acids and you know excetera? Anita Oberholster 19:52 Yes, good question. So here's the thing. There's one study that looked at this and showed that translocation from the leaves to the grapevine bunches is possible. Now here's the problem, we think it's very limited, because we still see more advantage from having a canopy there than not having a canopy. So here's the thing. There's a study that looked at a big canopy that looked at leaf removal before smoke, and then looked at leaf removal after smoke. Now, having the big canopy resulted in grapes with the least impact from the smoke than those that had leaf removal before smoke, worst impact as you can think, because the berries were totally exposed. And then the leaf removal off the smoke did help with the smoke impact in the final wines. However, there's other studies that didn't see a great impact by doing leaf removal. And there's a risk with doing leaf removal. Because if you do leaf removal, and there's another fire, or more smoke than you might do just made it worse. And obviously we are in California, you actually sometimes need some shade for your berries. So we are concerned about sunburn and other things like that. So we're not, even in Australia, I've talked to them as well, they're not recommending leaf removal, we think that risk is too high in the benefit too low at this stage. We are I'm just started a study at Oakville experimental station where we can look at translocation between leaf and vines a little bit more and get a better and I should say leafs and grapes and get a better idea about the kinetics of this translocation. When does it happen? Does it only happen when you also have sugar translocation happening? We would no more than a couple of years. Craig Macmillan 21:32 That's good. And I hope that everything continues apace. I'm very pleased to see how much research has been funded in this area. And also the collaboration. I think that the whole West Coast working together I think is a fantastic thing. And I hope that we can continue that model going forward. This isn't one of those problems where you know, we got a supply side grower, and then we have a consumer, the winery. And often we draw a line between those two. This is an issue that somehow we got to find a way of working together on this, we've got to find a way of finding some balance in terms of what the outcomes are going to be or what's going to happen. At this point qhat do you what do you think about that? What are what are things that you've come across that seemed like they made the community that if you will function or where things just clearly were problems that were going to be really, really bad? In kind of the more like logistical, social, economic realms? Anita Oberholster 22:20 Yes, I guess communication is key, right. And I do feel that this is a heavy burden that should be carried equally by the grape grower and the winemaker, there's been a little bit of everything. You have the situations where some grape contracts were canceled with no rhyme or reason, it seems like. And then you have the situations where you have winemakers that talk to their grape growers. Made bucket fermentations with their grapes, brought them in, tasted together, looked at the data, had a discussion. And that's really optimal. So what I really would like to see is that before there's a smoke event, before harvest, right, in the offseason, there needs to be clear communication about how this process is going to work. You know, the grape grow needs to know, okay, what stands in my contract? Okay, what does that mean? When are we going to evaluate the grapes? Who's going to pay for the testing? Who needs to take the samples, take it to the lab? Do we do bucket fermentations? Who do the bucket fermentations? Who's going to taste these wines? And all of these things optimally should be about communication and a shared experience right effort between the grape grower and the winemaker, that's really the best situation. So for growers, I would say, talk to the winery and make sure that there are steps in place, don't assume they are there, make sure that they are actually in place and what they are, what's going to be your responsibility. How's that conversation going to go? If there is a smoke event, it's really important. But also for growers, you know, I'm recommending, I know that testing is really expensive. However, if you can, for crop insurance, you need a sample of each block of each variety, which is a lot. But even if you can just take a composite sample, you know, 300 berries in a bag. I mean 100 If you don't have a lot of grapes, in a bag, throw it in your freezer. Every couple of weeks from verasion. I would say our risk for smoke exposure really exponentially goes up from verasion onwards. So I would say from verasion, take a berry sample, throw it in your freezer. If don't need it, you don't need it. But if there's a smoke event, then you can go back to your pre smoke sample. You can have that analyzed with your harvest sample. And you can see what's the difference? Because the problem is we do not have public baseline. And we're at baseline I mean for the main varieties, what is normal for your area, what is the normal amount of volatile phenols. Because this is the problem we're all doing testing, and then say, now we're supposed to know what's elevated. How do you know what's elevated if you don't know what's normal. And then like I just said, you can get smoke impact without wine taint, right? How much elevation do you need before it actually results in a wine that's tainted, and that's what we're also trying to address. But we're only now this season will be our second year for baseline. Trying to determine baseline for the seven main varieties in California to at least as a reference when you get numbers back from the lab so that you can interpret it more easily. And we're also doing threshold studies in wine. That is, how much of these compounds can be in a specific wine matrix before it results in a decrease in quality. That's what we're trying to do. I call it the two bookends. If we have the two bookends, then contracts can be more specific, perhaps they can even have numbers in them. Now numbers is difficult because we just don't have enough data to know whether what is a good number to put in a contract. I mean, there's some numbers out there based on guaiacol and 4-methylguaiacol. That's only two of the seven free vlatine phenols. That doesn't even take the bound into account. So this is something I do want to tell a grower and this is really important. Crop insurance is based on only guaiacol and 4-methylguaiacol, only to marker compounds. Here's the problem, you may have smoke impacting your berries, and that guaiacol and 4-methylguaiacol number is below quantification limits, right? So you think you're good, no problem. The issue is most of these free volatile phenols depending on when grapes are exposed to smoke can be in the bound form. So you don't see it. But now the winemaker takes those grapes, he makes wine during the winemaking process, up to 30% of that bound can be released to free. And now suddenly you have a problem because it made wine that impacted but according to crop insurance, your data did not show smoke impact. And this is why we're really telling people to do small scale fermentations. And I know don't ask a grower to do fermentation is not a small ask. So that would be great if your winery was prepared to do it. But it's not that difficult. I do have a video on my website. I cringe saying this. But it was done overnight. But there you go, Craig Macmillan 27:31 There will be a link to that particular video, by the way, I think I thought it was great. I thought it was I thought was fantastic. It is a little intimidating, I have to admit, but it was really, really good and a lot of numbers and a lot of things. But but you got it, you got to do it, you got to do it. Right. I mean, there's no other sense. Anita Oberholster 27:45 I think, you know, I tried to on the fly, in my brain, make it so that somebody in a kitchen can do it, using things that you may have at on hand right to make the wine. So the advantage here is crop insurance meeting us halfway. They said so long as you can show chain of custody, so long as I bucket fermentation actually represents that block for that specific variety, they will take that wine number so that one you can take that bucket fermentation and get that analyzed for guaiacol and 4-methylguaiacol. That may still show safe and then why may still end up being smoke impacted six, nine months later that unfortunately do happen. However, your chances is much greater that it will show you impact if you had impact just because you had that 20 to 30% that can be released during the primary fermentation process. And this is why we recommend that. Now that you know the story gets convoluted because there's some people now saying but grape analysis and wine analysis gives you the same number. There's some researchers out there saying that. And it's true for how they looked at the grapes, the grape number and the wine number was the same. However, most labs will take the grapes, homogenize it spin down the juice and analyze the juice. That's not an extensible amount of skin contact you really to get the same amount that will end up in the wine, you need at least five days of contact. Craig Macmillan 29:15 Okay, there is the key. Anita Oberholster 29:16 And so that's why I'm saying just do not do a mini fermentation because you need that skin contact time. Researchers that say that grapes on wine they get the same number by analysis is because for their sample prepping the grapes, they did something like a five day course. Craig Macmillan 29:31 But also because if you have an active fermentation, you are having some enzymatic activity that's going to break those glucosides and set those phenols the variable freeness free and that's what's happening in reality. So that's that's part of it. Anita Oberholster 29:45 Good point. So this is what happening. Yes. So especially in the beginning, as soon as you crush your groups, there's enzymes within the cells of the groups and then gets released and they can release the sugars from the volatile phenols. Now during the winemaking process in the beginning until the alcohol formation gets too high, the alcohol do inhibit these enzymes, you get that release. And then after that, you also have the fact that wine has a low pH between three and four. And so you get some acid release as well, because they're acid liable, meaning that they do release the sugars over time. But that type of reuse is slow. Craig Macmillan 30:24 That's a good question. Is there an unknown effect of pH on this? You know, you talk, you talked about a target pH that many winemakers would like to have. But I know that it was along the central coast, it's not unusual to be three, seven push and three, eight going from there. And in other spots, making white wines with three twos. Do we know what the what the effect is? Anita Oberholster 30:42 Okay, so here's the thing, I'm not recommending acidifying your wines to a ridiculous low pH and then adjusting it to get to get more to release. The thing is, there is a pH effect, but it's not very strong. So in the range of wine, this is why after wine is made, these bound compounds are actually pretty stable over five, six years, you may get another 10 15% releasing, okay. So that they don't actually release a lot at the wine range pH. So in a short period of time, I don't think it's worth doing that kind of thing. Just to give you some context in the lab, if we're trying to hydrolyze basically to remove all the sugars from the volatile phenols. We adjust the pH with hydrochloric acid or sulfiric acid to pH one. Craig Macmillan 31:33 Oh my god! Anita Oberholster 31:34 Then we heat it at 100 degrees Celsius for one hour. And it still does not release that. Craig Macmillan 31:43 Holy cow. Anita Oberholster 31:44 So just want to say this is extreme conditions. Because you know, in 2020, somebody contacted me and asked that winemaker wants me to spray to tartaric acid on my grapes to break down the glycosides. Now, obviously, that is a lot of unnecessary labor, because it's gonna do nothing to those bound, volatile phenols. Craig Macmillan 32:05 That's gonna be an uncontrollable situation, man. Anita Oberholster 32:07 Yeah, so that kind of thing. You know, I have to say, I want to invite growers. If somebody asked you to do something weird, or something you think is really not needed, you're obviously free to contact me and I will share my knowledge which they may forward to the winemaker. Craig Macmillan 32:24 Well, it's part of the communication. Anita Oberholster 32:25 I actually have a cooperative extension specialist for the for the enology side for the wine side, I true believer, all wines, and all good wines are made in the vineyard. Yeah, I you know, I'm a farmer's daughter. So I get it. So I really do want to look out for both sides. Because where would a winery be without grapes? Craig Macmillan 32:45 And where would a grape poor be without wineries? Anita Oberholster 32:47 Exactly right. So it's a two way street. And we need to figure this out together. You know, it's a difficult situation. And unfortunately, we don't know that much more than 2020. But I think we know more about how to prepare ourselves. And sometimes not, you know, knowledge is power, even just knowing what we don't know, is power. And just being more informed is power, right? The more you understand about the problem, the smaller the chance that somebody can come and tell you something that's totally wrong, and get you to do something that actually makes matters worse, which wastes your time or waste your money and is not going to help. Craig Macmillan 33:27 So we only got about another minute here left, we got to wrap up. What, is there one thing that you would recommend to a grape grower on this topic related to this topic? Anita Oberholster 33:37 I would say please store berry samples. Buy a freezer, and store samples. There's so many people that's now in litigation, and they asked my help. And I can't help them because they don't have a grape sample. And even the sample you sent to the labs that were smoke impacted those samples. Keep reference samples of them too. You never know when you need to go back to them. It breaks my heart when I can't help them prove what they're trying to tell me because they just don't have the samples to analyze. It's really important and and please talk to your winery, make sure that you know what steps to take. Talk to your crop insurance know what steps to take to ensure that you're at least covered if you need it. Craig Macmillan 34:25 Where can people find out more about you and your work? Anita Oberholster 34:28 So you know, I'm on the viticulture enology, the Department of Viticulture and Enology website, just look under personnel. I'm there, my contact details are there. There's a link to my bio and some of the work that I do and you know, just send me an email. It's very important to say persistence is key. I do receive more than 100 emails per day. So it's sometimes difficult to get to everybody and sometimes I really miss important emails. That's a shame. So it's really good when people actually send a repeat. Craig Macmillan 34:59 Okay, Hey, good advice. So our guest today has been Dr. Anita Oberholster Professor Cooperative Extension Enology in the department of Viticulture and Enology, UC Davis,. Thank you so much for being a guest. This is a hugely important topic and obviously isn't going away. And the science on this is developing. Golly, probably by the month. You know, as I watched the literature, there's new publications on this topic globally. Every issue of something so keep up the good work, keep us informed. We'd love to have you back in the future and we'll talk some more about what we learned. Anita Oberholster 35:29 Absolutely. It was great talking to you Transcribed by https://otter.ai
