145: New Class of Compounds Linked to Smoke Taint in Wines

As researchers were creating a training procedure to identify smoke tainted wines, they made a breakthrough discovery that links a class of sulfur-containing compounds called thiophenols to the undesirable ashy flavors found in impacted grapes. Elizabeth Tomasino, Associate Professor, Department of Food Science and Technology at Oregon State University explains that early research believed that the culprit for smoke taint was phenols with an alcohol group. But just adding volatile phenols to untainted wines did not produce the undesirable BBQ flavors. Research is still young but this discovery could help researchers come up with more effective mitigation strategies.

References:

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

My guest today is Elizabeth Tomasino. She is an associate professor in the Department of Food Science and Technology at Oregon State University. Elizabeth, thanks for taking time to speak with us today.

Elizabeth Tomasino 0:12

Well, thank you for having me. It's it's been a little crazy with conferences are back in person this year. So I'm actually at the Institute of Food Technology Conference in Chicago right now.

Craig Macmillan 0:23

Well, thanks for taking the time.

Elizabeth Tomasino 0:25

Oh, it's fun and lots of interesting information to talk about.

Craig Macmillan 0:29

The reason we asked you to be on the show is you and your colleagues to make kind of an interesting and possibly really amazing discovery regarding smoke impact on grapes and how that translated into Smoke taint in wines. First just so everyone is on the same page, what's the very simple definition what is smoke taint?

Elizabeth Tomasino 0:46

Smoke taint is essentially if there is a wildfire, lots of smoke in the air, that smoke gets into the vineyard, when there are grapes on the vine, the grapes can absorb the smoke compounds that smell like smoke. They then get sort of bound up in the grapes. So you don't you can't taste anything, but they're there. And then during winemaking, they're released. So all of a sudden, you can get a very smoky, ashy aftertaste in your wine. And if it's strong enough, it can be very negative for quality.

Craig Macmillan 1:15

And when are the grapes most vulnerable?

Elizabeth Tomasino 1:17

So this, is this is up for debate a bit generally it is thought after verasion. But some varieties might be different. There is some research going into this that some varieties might be susceptible earlier, and others may be more susceptible later during the year.

Craig Macmillan 1:33

There's been a lot of activity going on globally, Australia's done a ton of work. And we've got a lot of work going on on the west coast. It's really exciting to see the collaborative work between the different states and the different university systems addressing this problem. Obviously, a couple of years ago, it was devastating in Northern California. And we also had issues along the central coast here, which led us to wonder what was going on because people in San Luis County were affected by smoke from Monterey County. So it was traveling a long way, that really, really makes everybody extra nervous. Your work recently has identified a new class of compounds associated with smoke impact that correct?

Elizabeth Tomasino 2:11

Yes, we've been looking for it for a while. So some of my speciality in research and wine research is figuring out the compositional elements that cause specific sensory. So smells, tastes, wine has got hundreds and hundreds of compounds. So it's not as easy as saying, oh, one, one thing equals one smell. It's not that simple. And as you said before, the Australians have done a great amount of work over the years looking at these phenols that are found in smoke. But if you take a wine that's not smoke tainted, and you add high concentrations of those phenols to the wine, it doesn't taste like smoke taint, which means those are not the compounds that are causing that ashy taste to smoke tainted wines. So we've been doing quite a lot of work. And it actually came about in a roundabout way from how we originally thought. So many people were asking us about, they needed a training standard to understand what smoke taint was. So they're properly evaluating their wine. So we finally managed to come up with a smoke taint training standard for people that that is exactly what happens, the sensory, ashy after taste of smoke tainted wine, and we said, hey, that's really representative of smoke taint. Let's go analyze that. So we analyze that with Tom Collins an assistant professor at Washington State University. And we found this new class of compounds. And then we analyzed a bunch of wine that had been exposed to smoke, as well as wine that hadn't been and saw hey, these thiolphenols. So similar to the phenolic, the Australians found but there's sulfur groups on it. So it makes them very potent compounds. So thiolphenols that were found at higher levels in smoke tainted wine, and in some subsequent sensory, we added thiolphenols to a non smoke tainted wine. And lo and behold, in sensory analysis, they were rated as being smoky and ashy, of smoke team for it.

Craig Macmillan 4:07

Wow, I'm assuming that this is a class of compounds that was already known to exist that just hadn't been associated.

Elizabeth Tomasino 4:13

You know, not really thiols, the overall thiol class of compounds is well known but thiolphenols we found one reference to it in a textbook in the 60s linked to burnt meat, it's not normally looked at and food a lot and so that I think that's one of the reasons number one, no one, no one had thought to look for them because when you think about thiols in wine, you think about Sauvignon Blanc and tropical fruit flavors. I think they individually smell like burnt hair and burnt meat and things like that. You don't normally think about that. And within the food industry, they don't measure them. So it really was really was sort of fortuitous that we had this standard that had high levels. And then we started realizing that like everything we know to cause problems in in smoke tainted wines. And all these things the wine industry was telling us really made a lot of sense with the chemistry of these new compounds.

Craig Macmillan 5:06

Let's talk a little bit more about what phenols are, very light and very volatile.

Elizabeth Tomasino 5:12

Yes, well, they're essentially the breakdown products of lignin. So lignin is the main structure of trees, lots of plants. And when you add heat and burn them, while there are many things that come out of them, phenols are one of those classes. So they're ring structures with an alcohol group off one of a benzene ring with an alcohol group as it is a basic phenol. And they're very much have the smell of sort of that old campfire. That's, that's the smell of them put together. But in thiolphenols instead of an alcohol group, it's a sulfur group. And that changes practically everything about the compounds.

Craig Macmillan 5:46

I've been talking to some other researchers. And we talked about the idea that some volatile phenols are found naturally at low levels in fruit potentially, but also possibly barrels, things like that. So certain phenols are not necessarily coming just from the outside, they may actually be a baseline level in fruit or wine starting out. Is that right?

Elizabeth Tomasino 6:08

Yes, I do want to say specifically to what we know to date, what we talked about free phenol. So phenol is not bound to anything else phenols that are aroma active so you can smell them. They are found in a lot of grapes at low levels, not enough that you'd really smell or taste it. When you toast oak barrels used in wine or oak based products. They're formed. Again, there's lignin in the oak, so they're formed that way. The one question that that is still a little up in the air is we don't think the bound phenol compounds exist freely in grapes, we do think that is really related to smoke exposure, though, of course, I know some people are doing research on it. So maybe they're gonna prove that wrong or, or correct in the future for it. But the free phenols low levels, definitely in grapes, different concentrations, depending on the grape variety. So it's not a one size fits all. And of course, you also have very different oak species in oak barrels. So there's some differences there. So so that's what has made a lot of this challenging is that you do have some of these naturally in grapes and wine. And then in the past, we've been looking at really elevated concentrations of those phenols. And what's exciting with the thiophenols. And again, we're so early in the research is we're pretty certain they don't exist, unless there's a smoke exposure effect these these thiophenol specifically, you know, we've got some work we're going to be looking on. But we do think they might be really good marker compounds because they're not, they're definitely not found in oak barrels.

Craig Macmillan 7:36

That's, that's really awesome. That's really fantastic. That really opens up a new world. This is I hadn't thought of this question till just now what is our ability to test for these, this does exist commercially.

Elizabeth Tomasino 7:47

Unfortunately, they are just as complicated if not more, as some of the phenols. So the issue with these compounds is so if we think about concentrations and decreasing concentrations, phenols that we've looked at in the past run at microgram two milligram concentrations, then you go down by a factor and you get nanograms per liter. And it looks like these style phenols are at picograms per liter, I have never actually worked with picograms per liter. So there's and they're very sticky compounds. So they react. So you first have to to measure them accurately, at least you first have to sort of, we call it a derivatization. So you add something to it to make it way more stable, less volatile, and then you have to concentrate them. So the sample prep is actually quite extensive. And I know we are working with some people to see if there are ways to speed it up or make it not quite as time consuming, but unfortunately they are they are kind of a pain to measure.

Craig Macmillan 8:47

So it sounds like sensory analysis is really our only tool at this point.

Elizabeth Tomasino 8:52

We do have some chemical analysis. So we're actually adapting a method that we've done for those more tropical fruit styles for it. But we still recommend because it will take some time to know the accuracy of the methods and other things like that we still do highly recommend doing microferments with sensory for it and particularly for this season potentially next season we might have some more testing available but as I just said there they are difficult to measure.

Craig Macmillan 9:19

Are there specific descriptors related to and what are the compounds for the volatile phenols we were looking at before and specific descriptors for the thiophenols it'll help people kind of identify.

Elizabeth Tomasino 9:31

Of my knowledge so the phenols we currently looked at guaiacol, o-Cresol, p-Cresol, it's actually very reminiscent of a bit more of a chemical even a little bit of a bandaid aromas to them when you put them together. Thiophenols the ones that we've determined at the moment we do know there are others but but we have to confirm which ones they are thoiphenol, thioguaiacol, the thio-Cresols, burnt shows up in every single one of their descriptors, burn hair, burnt pork, burnt rubber. It's that very strong burnt aspect of it.

Craig Macmillan 10:09

Which is maybe a little bit different than smoky campfire.

Elizabeth Tomasino 10:13

We found in sensory that when you put the phenols together with the thiophenols, that is smoke taint. So the combination of the two classes is really smoke taint. But as I mentioned before, we currently don't think the tihophenols are found in grapes, and they're certainly not an oak. So they might be they might be much better predictors in the future. There'll be a lot of work over the next year. But that's the current hypothesis, at least.

Craig Macmillan 10:38

Does different types of fuel impact, what kinds of compounds are going to be released in the air?

Elizabeth Tomasino 10:43

So yes, they will. A lot of research, we look at barley, and haze and things like that, because it's really lignin. And of course, all plants have lignin. So that's something across it. But different trees will also have other compounds. So for example, I know up and WSU, they burn sagebrush a lot, that the smell of it is not just smoke, there's other aspects to it. I know this year, we've collected some forest floor things in Oregon to see how Oregon compares to what we use in research, which is really primarily just lignin for it. A lot of the smoke taint work is really what would be found across all smoke for it. And then we're starting to look at the differences between the fuel so you know, what's an all smoke lignin based products or an all smoke, and then you'll start to get some of those very different, you know, fuels. And I'm not even going into burning buildings, that's a totally different thing. I'm just talking about plant material.

Craig Macmillan 11:42

Well, the whole other area when the town burns down, no, we have to worry about that. But we did in you know, in Napa and Sonoma, we've had massive burns as well. That's part of the whole picture. This just reminded me of something else. So you're talking about, you know, trying this and trying then when are folks experimentally exposing grapes to smoke?

Elizabeth Tomasino 12:00

Yes, I call it when we talk about things because of course I'm in I'm in charge of a large USDA grant, we have protocols for if we have what I call a natural smoke event, which thankfully, this year, fingers crossed has not been too bad. And then we also have our research smokes, because of course research still needs to happen even if there isn't a forest fire. So we actually build very big tents and cages and things enclosed grapevines and smoke them out.

Craig Macmillan 12:27

Well, you're making a grape smoker.

Elizabeth Tomasino 12:29

Essentially, yes.

Craig Macmillan 12:30

Do a brisket.

Elizabeth Tomasino 12:31

Uh huh.

Craig Macmillan 12:33

That's incredible that that must be quite a quite a project.

Elizabeth Tomasino 12:36

It takes quite a few students to get it set up and running each year. So.

Craig Macmillan 12:41

Has this discovery indicated any new directions, or any possibilities or any thoughts and creativity around mitigation strategies?

Elizabeth Tomasino 12:52

I think it's going to change the game for mitigation. So there's been a lot of work in mitigation without having been hugely successful. And phenols as I said before, the chemistry and the reactivity of phenols is hugely different from thiophenols, we've essentially been using mitigation strategies for the wrong compounds and sulfur compounds are highly reactive. So and we know a lot about them. So reductive aromas and wine are sulfur based compounds, we actually think it's going to speed up some mitigation. And we're going to have some some more things, winemakers can actually do that are going to be more successful, because now it's really, really there. There isn't a lot you can do for it. But again, we've been looking at the wrong type of techniques based on the chemistry of the compounds.

Craig Macmillan 13:43

So since we're looking at different types of thiols, are we talking about the same kinds of strategies at the wine level that a winemaker might use if they are had dealing with hydrogen sulfide, or captains or something like that.

Elizabeth Tomasino 13:57

So thios are a type of mercaptains and another name for thiols. And if you really go into your oxidation reduction chemistry, one of the things that we're going to be investigating strongly is thios are one form, they're sort of reduced form of this compound, really low perception threshold. So a little bit smells very strongly. If you change the form of that into the disulfide. That's not as strong, it doesn't have a big of a sensory impact. So when a lot of people are talking to us about these things that they've noticed in their wine, and we sort of scratched our head, we're going back and thinking about it now going, oh, this is oxidation reduction chemistry, like redox. It's making some sense if you think about it from a redox potential standpoint. So it is looking and into those aspects specifically, and there are things people do for oxidation and reduction. I was just talking to someone you know, someone said, Oh, add copper sulfate. And I'm like they used to do that but but it's cyclical in wine. So you have to remove the copper sulfate that's bound with the sulfur and there are some techniques out there that you can do that with it.

Craig Macmillan 15:03

Are there things just in general that growers should or should not do if they see that there is a smoke event headed their way to reduce smoke impacts on grapes?

Elizabeth Tomasino 15:15

Well, first off, they should be safe for what's happening where they are with with what's going on. For it, I think it's something to not panic. A lot of people I know, in 2020, we didn't know as much. A lot of people said we had an event, I'm not going to do anything with these grapes, just because it's so different based on the variety. And we are starting to have an understanding of which smoke is problematic. Just because you were near a fire doesn't mean you're going to have a problem. Just because you're far away from that fire doesn't mean you're not going to have a problem. So do go out, pick some grapes, do some small scale ferments, taste those, smell them, don't panic, again, do those microferments maybe get get a sample or two analyzed and then make a decision what you're going to do. I do not recommend making a decision, just hey, we had smoke in the vineyard, we shouldn't do anything. It's not that easy for it. So we do recommend, they don't have to pick all their grapes, but go out and pick some of the grapes, do a little ferment and then figure out if you want to pick your grapes or not

Craig Macmillan 16:17

Don't freak out.

Elizabeth Tomasino 16:18

Yeah. And it's hard because of course, it's a very, very sort of upsetting situation, but but I've seen samples where a fire was a mile or two away. And just based on the variety in the winemaking, they did they were fine. And one variety, versus another variety that it was awful for. And I know a lot of people picked grapes that weren't shouldn't have been picked in 2020. And I know people didn't pick grapes that should have been picked for it. And I think it's because we just panic for it. And I know it's hard to do that. But take a deep breath, get a couple of grapes samples, Do, I think UC Davis has some of the small scale ferment procedures up there and how to do the sensory. Taste your wines. Make sure you have several different people tasting with you because people have different sensitivities to smoke taint. And then sit down and make a decision about what you want to do.

Craig Macmillan 17:07

Another concern is the development of aromas over time. So initially, something might smell clean or fairly clean. But then over time, something starts to express itself. Is that accurate? Or is that something we're kind of like making up or afraid that will happen?

Elizabeth Tomasino 17:27

Actually, I think that is accurate to some point, there will be a point where the smoke taint won't necessarily change a lot anymore. And as I said before, an understanding of these new compounds are greatly going to change, you know, understanding the conditions. So for example, if your wine smells fine, you put it in bottle, and it develops over time. But you created a very reductive environment. So maybe your disulfide form change to the thio form. And then that's happening there. So yes, it will potentially still happen. But as we're learning new things about it and new treatments, we're gonna have a much better understanding of what to look at before you bottle it to see if you're going to have a problem later on.

Craig Macmillan 18:06

Again, coming back to mitigation or prevention, can I spray something on to the fruit that will prevent these aromatic compounds from getting into the flesh?

Elizabeth Tomasino 18:19

That's what we'd love to have first step right first step, well, first step don't have forest fires that is a little bit outside of my control. Second step, can we stop the compounds going into the grapes? There's a lot of people looking at a lot of different coatings and sprays and things. And unfortunately, that research takes multiple years because of course, the climate is slightly different each year. So I know a lot of people are working on it, I think we're going to have some options to not maybe stop it from going into the grapes are greatly reducing what goes into the grapes for it. And hopefully in the next next year or two. We're going to have some some better options and some information as that as a potential preventative step.

Craig Macmillan 18:58

If I spray something in the grapes are still wet, is that going to make it easier for for volatile compounds to get in? Or is that alone going to help?

Elizabeth Tomasino 19:07

So a lot of sprays fungicides, things like that, that are used have oils, lipids to them, it's what makes them stick to the grapes, what makes them effective, and phenols can dissolve into those and be transferred into the grapes. So I know in Australia and Anita Oberholster at UC Davis has done some work, looking at if any sprays can prevent them from going in or make things work. And I want to say the vast majority of them actually increase the smoke compounds in grapes. So they're not as effective. A lot of the work is being done on non traditional sprays or things you wouldn't think about. I work with Dr. Yanyun Zhao at Oregon State University. She's known for edible coatings for post harvest effects. And we're looking at developing some of these coatings to to block or trap the compounds from getting into the grapes for it. And I know Tom Collins is looking t some stuff, as is Anita as well, but they're very non traditional coatings, because of course, you don't want those oils and lipids and things, goods.

Craig Macmillan 20:09

Good to know. What about the timing of harvest? If I again, if I have an idea that there's a smoke event coming my way, in theory, I could go ahead and pick that fruit ahead of time and get it out of there. Where are my questions kind of coming from is that the if I understand correctly, the the particulates of smoke and the volatiles phenols or thio, phenols and smoke, they're totally different things. It just happens that the volatile compounds travel with the with the particulate do the is there a possibility that the phenols, the volatile phenols and the thiophenols travel ahead of the particulate and the reason I ask is do I need to worry about something before I see it?

Elizabeth Tomasino 20:47

So first off to my knowledge, thiophenols don't occur in smoke .Phenols occur in smoke. Phenols get absorbed into the grape, and then you have a lot of metabolic processes that occur, that that creates thiophenols for it. So we're still in least, at the moment, we're still looking at phenols from smoke specifically for it.

Craig Macmillan 21:08

Interesting, interesting. So the thiophenol was actually formed later?

Elizabeth Tomasino 21:12

We think and again, totally theoretical at this point in time, we think that the phenol levels get so high in the grapes, that it's almost like a detoxifying event, and it starts going through other metabolic pathways, one being the ones that create these thiophenols. And unfortunately, they're also bound to other compounds. So you still don't taste them in the grapes. Because they're bound, they don't have an aroma. And it is during fermentation that it releases that just like the traditional theory of phenols and phenol glycosides in in grapes for it. I work with a range of climate scientists for it. And they literally say if you can go outside and smell it, then you've got the compounds there, the vast majority of the time, you will be seeing smoke, so you don't have to worry about oh, what's going to come in there. And I'm not going to I'm not going to know, these compounds are also very reactive in air. So you can see smoke, but not smell them. Because it's not as simple as saying time or distance. But for instance, I think guaiacol within a number of six to 12 hours, it reacts with ozone and other things in air. So you don't have guaiacol anymore. If you have a very windy day. Of course that could mean that traveled very far versus a not windy day. It's not as easy as saying if your x miles out you're fine. Totally depends on the day. But but actually you you would it would be very rare. I can't think of one instance where you'd actually not see smoke and have those particles normally it's you'll see smoke and is the question. If you go there, is it really smelly or not?

Craig Macmillan 22:44

I interviewed a Anita Oberholster to the other day, and she was talking about the concept of the freshness of smoke having a potential impact. Does that idea come into your work at all?

Elizabeth Tomasino 22:56

Yes, it really comes into how much phenols. So the closer you are to the burn site, the less chance those compounds have had to react yet, so you're gonna have higher concentrations of phenols. So again, if you have a burn right next to your field and the wind is blowing into your field, you're gonna have a lot of those smoke compounds versus you know, there were there were smoke from Northern California went into Southern Oregon a little higher, they didn't have as much smoke compounds in their grapes, because of course, it was very far away from the actual burn ignition site. Now, that doesn't, to say that some of these huge fires, you're not going to get impacts far away. What I'm learning about fires and how they move in different layers of the atmosphere is if it's big enough, and if the air currents are going strong enough, far away can have a problem. But generally, the closer you are to the actual burn site, the higher those smoke compounds are. And that's where we talk about fresh or new smoke versus old smoke.

Craig Macmillan 23:54

Fascinating. Yeah, cause some cases we've had the cloud, the plume travel quite a long ways. And then the question is, well, how, you know, how much danger are we in in 2020 I saw we really did have differentials, some varieties picked up a little bit others were fine. And we just are like, well, that's just how it is. We couldn't really predict what was going to be what. So again, getting back to your point, just hang in there. Don't freak out. Try it out, see what's happening. Because at this point, we really can't kind of predict. What is one thing you'd recommend to our listeners around this topic protect particularly grape growers, but also winemakers?

Elizabeth Tomasino 24:33

I think grape growers and winemakers, there's a lot of information out there. Each of the states are grape growing wine growing associations have a lot of up to date resources for it. Talk to your extension people. We always have a lot of people who said hey, I did this. You know here I heard about this and it's not based in science. No one has tested it. There's been a lot of work out there. We're trying to make sure you don't waste your time on something that doesn't work. So please go to those places first before you try it. And as I said before, take a deep breath, go out and do some microferments, taste your wines, maybe get some analysis done, then sit down and make a decision. Again, I know it's a very stressful thing that happens. But we do feel very strongly that sort of people panic in the moment, and it's like, okay, you know, sit down, we know enough about things that your grapes could be okay, let's see if they are.

Craig Macmillan 25:29

That is a really good message. Where can people find out more about you and your work?

Elizabeth Tomasino 25:33

So Oregon State University and the Oregon Wine Research Institute does have a smoke grape smoke exposure page, the grant that I am project manager for, we will soon be working on having a website up through Oregon State University. For that we're trying to get set for this season. So that that got to the wayside at the moment for it. There are of course, extension articles and things out there, you can sometimes just type in my name with wine and smoke and see what pops up.

Craig Macmillan 26:02

Thank you so much. We'll let you get back to your conference. I am so grateful that you were able to take time out to talk to us today. It's a really important topic. And one, it's it's breaking news. We're hearing new things all the time, which is really exciting. I think that the the way that the science community has jumped on this is really laudable and really important for the industry all over all over the United States actually, and the world, quite frankly. So thank you for your work. Thanks for talking to us. Keep keep going. I hope that you have a lot of success, a huge team that's working on this and I think that that's gonna lead us down the road faster than if we didn't. So I really appreciate what you folks are doing. Our guest today has been Dr. Elizabeth Tomasino. She is associate professor in the Food Science and Technology Department at Oregon State University. Thanks again, Elizabeth. This has been great.

Elizabeth Tomasino 26:51

Thank you very much for having me.

Transcribed by https://otter.ai