Come Rain or Shine

Talking Wine, Weather, and Science: Part 1

February 03, 2021 USDA Southwest Climate Hub & DOI Southwest Climate Adaptation Science Center Season 2 Episode 2
Come Rain or Shine
Talking Wine, Weather, and Science: Part 1
Show Notes Transcript

Do you drink wine? Do you know how many varieties of wine there are in the world? What’s enology? What makes a vintage unique? Join us as we sit down with three scientists who specialize in viticulture and the cultivation of wine-grapes to hear about all of this and more. Dr. Kerri Steenwerth, with USDA-ARS in California, Dr. Andy Walker, from UC Davis, California, and Dr. Jeremy Weiss, from University of Arizona, tell us why the study of viticulture is important to them, how they got into the field, and what they do in their professional calling. Be sure to listen to Part 2 as well, where we delve into how our changing climate might affect wine production in the future. Image by Photo Mix from Pixabay.

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Emile: [00:00:00] Welcome to Come Rain or Shine, podcast of the Southwest Climate Hub and the Southwest Climate Adaptation Science Center or CASC. I'm Emile Elias, Director of the Southwest Climate Hub. 

Sarah: [00:00:12] And I'm Sarah LeRoy Science Communications Coordinator for the Southwest CASC. Here, we share recent advances in climate science, weather, and climate adaptation and innovative practices to support resilient landscapes and communities.

Emile: [00:00:27] We believe sharing this information will strengthen our collective ability to respond to impacts of climate change in one of the hottest and driest regions of the world. 

HI & welcome to another episode of Come Rain or Shine today. We're here to talk about viticulture, which is the cultivation and harvesting of grapes, and also touch on enology, the study of wine.

Grapes give us many of our everyday supermarket products, of course, from fresh fruit, raisins, juice, grape jelly for PB and J's, and the U.S. wine industry alone is a multi-billion dollar industry. In 2019 U.S. wine sale revenue, including both domestic and imported wine was more than $72 billion. And wine is also personal. How many of us have saved a bottle for a special occasion? 

2020 brought changes in nearly every part of our lives and wine was no exception. While U.S. wine sales at restaurants, bars, and tasting rooms plummeted, the uptick in grocery and online wine sales was amazing, forcing U.S. wineries to market and sell online.

In addition, 2020 extreme drought and wildfire led to concerns about fruit blight and production in parts of the U.S. So what goes into getting these grapes from the vine to the table and how might weather and climate factor in? Today we're speaking with three experts in viticulture and climate.

Dr. Jeremy Weiss is a climate and geospatial extension scientist at the University of Arizona working with wine grape growers in Arizona, and yes, wine is grown or produced in every state of the nation. 

Dr. Kerri Steenworth is a research soil scientist with the USDA Agriculture Research Service in Davis, California, and she's working to develop ecological approaches for sustainable vineyard-floor management, and to determine impacts of management practices on weeds, grapevines, soil microbial communities and soil quality for California viticulture. 

Also in Davis, Dr. Andy Walker is a professor in the department of viticulture and enology at UC Davis focused on the development of new disease resistant cultivars.

The big thing that probably comes to mind for many is that without grapes, there wouldn't be much wine. So speaking as a wine enthusiast and I'm definitely not a connoisseur, I personally think it might be obvious why we should care about viticulture. That said, I'd like to ask each of you why you think it's important for us to talk about viticulture and I'll start with you, Kerri.

Kerri: [00:03:12] Thank you, Emile. I think actually that Andy might be the best one to take on this question initially, given that he's been working in this area of research for quite a long time, but I'll take a quick stab at it. For me, it's important to study viticulture because it brings together, the product brings together families and friends to spend time together around a dinner table.

That's what I think about when I think of wine. It's also quite a vibrant system to study as a research scientist and the people that work in this industry are also very innovative. It's a fascinating community to work with, and everyone is always trying to push the envelope to try and improve the production system. So it's for me, a very interesting place to work. 

Emile: [00:04:03] Great. Thanks Kerri. Andy, did you want to add on to that? 

Andy: [00:04:08] Sure, sure. Viticulture is probably one of the oldest agricultural professions that exists. And I always argue with a lot of plant geneticists and evolutionary geneticists about when viticulture evolved and how it developed.

And I say, well, of course it developed first before grasses and grains and pulses and corn and peas. You don't need those things, right? You would need wine. And why? Well, wines red, alcoholic, it has tremendous philosophical and societal implications about, it just evolved with us, I think, more or less, and it ferments all by itself. So it's really not a very difficult process to generate or sort of control sometimes.

Emile: [00:04:46] Excellent. Thank you. And Jeremy, uh, why do you think it's important to research and study viticulture.

Jeremy: [00:04:54] Well to add on to what Kerri and Andrew just mentioned. Certainly history is part of it. Viticulture, wine-making, go back at least two to three thousand years in Europe and regions to the, to the east of there, if not prior to then. 

Culture is a big part. A lot of national identities are tied up in viticulture and wine making. France and Spain and Italy are some of the countries that quickly come to mind for almost anyone when asked about that question. And it's tied up in various aspects of that national identity, like cuisine, for example. 

For me another aspect of it is travel. When you think about where a wine comes from and it's grown throughout the United States made throughout the United States, throughout the world, and many, many regions, you're able to transport yourself,  especially this past year when we couldn't travel. Uh, to other parts of the world, and again, learn about the history culture of those areas, in addition to the wine product you might have in front of you. And of course there's money involved in this.  In the introduction, Emile, you mentioned how it's worth tens of billions of dollars in the United States. I've read globally that it's on the order of a few hundred billion-and that's billion with a B-dollars, uh, you know, as an industry around the world. 

But more importantly when it gets to the local economies. And this is true at least in Arizona, if not in other States as well, the money aspect of it is really important. It can really be one of the leaders, if not the leading part of the economy in rural counties. And that's really important. It's not just the agricultural part of it, but also some of the businesses that support the growing of, of the fruit. Whatever supplies are needed in the vineyards, businesses like that. As well as wine tourism, uh, that's also a big draw for a lot of areas nowadays. 

Sarah: [00:06:53] Thanks everybody. So, you know, now that we know why it's important to study wine grapes and winemaking, we'd like to hear a little bit more about yourselves and how you came to study these topics. So could you tell us first a bit more about your specific area of research and what it is that you do, and then also how you got there? So why don't we start with Andy this time? 

Andy: [00:07:16] I began pursuing viticulture after doing a botany degree here at Davis in fact in taxonomy. And I went and worked in nurseries on landscaping, the various other pursuits for a while, and came back to school and decided to work on viticulture because of my enjoyment of wine and, and knowledge of that crop.

But the plant is an amazing. It's one of the more interesting plants that exists, all the ties to philosophical pursuits and societal pursuits and all the rest, all trace back and put it together. But taxonomically, it's fascinating. Um, the, the plant is actually, grapevines are actually like a lot of dioecious species, species that have male and female flowers, they're more like animals than they are plants oftentimes in terms of their genetics and how that controls. It's a fascinating crop to work on, it grows all over the world. People don't really realize that. And they're wild grapes growing everywhere from, from, uh, central, actually from central Oregon, down the west coast, all the way across the southern, the southern United States where it's warm then, everywhere.

In fact, when you're traveling, if you look out the window you're liable to see grapevines if you know how to look. So they're, they're a fascinating crop. Uh, and they, they have all the resistances we need to pests and diseases, these wild species. Uh, they exist everywhere and we haven't really explored them to their fullest extent yet.

So it's an upstanding portion of the business as well. So it's sort of tied my interest in taxonomy  and the botany, uh, with genetics and horticulture. As Jeremy mentioned, it's an extremely valuable crop and normally the number one agricultural pursuit and it, and it's really what makes horticulture in many parts of the world.

And we think of it as we talk about increasing diversity in crops to maintain the variation that we need to select the things, but in viticulture we've actually been sort of the opposite of that. We, we probably have over 2000 wine varieties in the world, maybe even closer to 3000, it's hard to know.

And a lot of those are the same, same variety under different guises and different names. Um, and they're spread all over the world, in very hot climates and very cold climates. And in fact, in California we grow grapes in the Coachella Valley where it was 128 degrees this summer, uh, all the way up to areas around Mount Shasta and, uh, and Mount, and um, and other areas in the northern part of the state that are quite a bit colder. So there's a lot of variation in how well they'll grow and then we haven't really exploited that. So when you think about grapes, you think about where they came from and how they developed. And there's always a tie with people, which is sort of an interesting component.

And we've gone now from taking varieties that grow regionally around the world to varieties that are known as the international 10 or 15. And we winnowed down our diversity, we've eliminated our diversity almost entirely, and now we're worried about how to adapt to climate change and things. And in fact, we have all the tools to do so already.

There's a lot of ways to approach that, we'll talk about that as we go along, but the first way to approach it is to accept the diversity and enjoy it because there are some remarkable wines that are made from different varieties. I don't think I answered your question very well, but it gave you a background of where we're at.

Sarah: [00:10:29] That's perfect, Andy. It shows your, your passion for what you study. So Jeremy, let's go to you next. How did you get to where you are and a little bit about your research. 

Jeremy: [00:10:40] Well, even though I'm in the climate and geospatial business nowadays, some people are surprised to hear that my background, my, I started studying in botany as well, just like Andrew did, except I was focused more on horticulture.

So I have that buried way back in my background. And it's been, um, an opportunity where I was able to start to piece together that diverse background, various topics into something. And I got started with the climate and viticulture work really through market demand. Arizona's viticulture industry is relatively young, the first American Viticulture Area or AVA as they're called, it didn't come around until 1984.

And our second one didn't come around until 2016. That's a pretty stark comparison when we're thinking about states like California, for example. Nonetheless, the state industry has really been growing, uh, relative to its size, of course, in the past five to 10 years. And there, you know, to my estimation, there really was no one providing climate information directed at the state viticulture culture industry.

Um, and this was a few years ago when I started to get into the work, nor was anyone providing climate change information directed at the industry. And so despite the real big uptick in scientific studies around the world on viticulture and the impacts that climate change have brought and potentially will bring, none of those studies -that universal information is relevant to growers in the state of Arizona- however, The growers were finding that none of that information was specific to the conditions here that yes, arguably will make a difference when it comes to an end product like wine. And so they were needing that information. And with my background, uh, I've been able to, um, fill that void as best I can.

Sarah: [00:12:49] That's great Jeremy, and in part two, we'll get more into the climate change piece of this. Okay, Kerri, over to you. How did you get to where you are and a little bit more about your research. 

Kerri: [00:13:02] Thank you, Sarah. So my research has focused on looking at the benefits and trade offs of different practices in the vineyard floor, and I'm really focused on looking at biogeochemical cycling, specifically carbon and nitrogen and how the different practices that occur in the vineyard system can build healthy soils and can also mitigate greenhouse gas emissions. I'm also really fascinated by soil microorganisms and what they're doing. Who's there, why they're there.

But I came to work in viticulture a little bit differently than Andy and Jeremy. I was studying soil science for my PhD and a lot of the agricultural soils that I had been exposed to. Not to slight annual crops at all, but they have to be, uh, grown on class one soils. Or maybe class two, and they're just not as interesting as the kinds of soils that grapes are grown on.

In California, grapes are grown on 11 of the 12 soil orders, which is the taxonomic classification and they exist in all different climates. And so for me as a soil scientist, I thought it would be the perfect crop because I could travel. As Jeremy mentioned, wine is associated with travel, and I could learn about all different kinds of soil types in the world.

So that's how I came to work in viticulture. I also really like working with the grower community and understanding what their needs are and what questions they have and how I can serve the community with information that we can generate through our research.

Sarah: [00:14:42] Excellent. Thank you. And so to wrap up, we have a little bit more of a fun question here. So as a scientist in this field, do you have a favorite vintage of wine that you like to drink? This is a question for everybody. Um, why don't we start with Jeremy? 

Jeremy: [00:15:02] I know we have a soil scientist in our conversation today, but I'm going to go out on a, on a limb and say weather is what makes a vintage a vintage. Or perhaps, you know, for the present day it's better said climate change influenced weather is what's going to make a vintage a vintage. So that said, it's interesting in a way that as I've been learning more about viticulture, you know, with regards to precipitation for example, and vintages. The fact that people can irrigate really takes some of the variability out of the vintage from year to year in terms of yield and the fruit quality.

And so if a grower is having to irrigate to have a successful crop, things are, have, that variability is lessened and you're really left with, in terms of climate, temperature ruling the vineyard. Sure, you can have events that can ruin a crop like smoke taint from wildfires and hailstorms. But in terms of, of where climate comes in, it's really temperature that is critical for viticulture.

And as I've been learning more about vines and phenology and physiology and the fruit quality and composition, temperature can affect things in so many ways, uh that it's really hard to keep track of. So in terms of my favorite vintage, I'm going to say those where temperature, have left, you know, where temperature has left its mark, and made things more interesting than not.

Sarah: [00:16:44] Very interesting. I, yeah, it's a very interesting thing to hear about the various vintages of wine and their relation to climate and weather. Kerri. Do you have a favorite vintage of wine?

Kerri: [00:16:59] Thanks for that question, Sarah. I think that Jeremy just talked about the effects of temperature and how that affects wine. I can provide a few anecdotes with respect to soil and how it affects wine. I went to a tasting that demonstrated that soils that had a lot of aluminum that was free due to the low pH in the soil that they had a different taste than the ones on a different soil type, just adjacent to it that had a more moderate pH. And Andy can help me out with the term there, the flavor of the wine that had higher, free aluminum in the soil solution that, that particular variety had more of a bell pepper taste, and there's a certain compound that provides that taste. But this is all anecdotal. And so for me, I think it's, the soil provides an interesting flavor.

I'd also like to make a plug for the microbes because there's a lot of work going on looking at how the soil, bacteria and fungi can contribute and affect the bacteria that's on the grapes. We don't actually know that they're causing flavors to be imparted to the eventual wine product, but I would bet in 10 years from now, we'll have a better idea about what's going on, um, in that particular sphere and how that affects vintages.

Sarah: [00:18:19] Okay Andy, let's end with you. 

Andy: [00:18:21] I can sort of wrap it up because I think if we combined everything that Kerri and Jeremy mentioned, we really end up with this concept called terroir, which has been misconstrued this to really insinuate that the soils make all the difference in the wine. Soils are a substrate primarily.

The thing that makes the big difference is temperature and rainfall. So those, I think those two things together are key. And around the world we grow grapes without irrigation in many places. California is not really one of them because of the lack of rainfall, particularly during the growing season where we end up, you know, there's no rain from May until October, most years.

And so that's critical, that has a big role in how we control vine growth. Sometimes there's far too much rainfall. And it's very difficult to control the vegetation and we add irrigation on top of that, which can make it even more of a component. So the idea is, is terroir really reflects all of that now. Instead of microclimate, the mesoclimate, the macroclimate, it's the rainfall, it's the soil, it's the whole, the whole package.

And it's very hard to define a vintage in California oftentimes, and maybe that's a bad thing, because our wines tend to be very typical for a region. Not distinctive within that region, oftentimes. And it is not because of the terroir it’s because of farming practices. It's because we're trying to grow them the same way with irrigation and with light management and canopy development.

So it, it's sad in a way, again, it's the lack of diversity. Once again, it's not just the diversity in the genetics of things it’s diversity in the way that we're growing them and how we're cultivating them. It'd be nice to have something more regional and then more distinctive. Uh, I frequently traveled overseas. I used to travel overseas a lot, and I'd get to places and say, I'd love to taste your regional wines.

And the growers would bring out things in the wine makers would pour them and then they would say, but please look at our merlot, or look at our cabernet sauvignon. You'll really be interested. And I'll say no, I'm not interested at all!

I'm interested in your regional varieties and how they might adapt to a broader picture in the world of the time. So I'm going to get out of the difficult question, which is, which is my favorite vintage by telling you that, there isn't one, I guess. And they're all...they're not homogeneous, homogeneous entirely, but there's a lot of similarities between them once you get a regional perspective. 

Kerri: [00:20:39] I have a question for Andy to follow up. That question, that, that statement about wondering what regional varieties, um, you might find in different places. I want to, I was curious if you think that might change with our changing climate, you know, that in order to maintain market viability, that different regions might try out new varieties that are better adapted to, you know, the, the extreme heat they might be experiencing or...

Andy: [00:21:05] That's very true. That part of the process has started already in many regards. And if you go wine tasting, you'll, you'll stop at the winery and there'll be 10 or 15 cases of something very interesting. Aglianico or, or Vermentino something. And you'll taste those wines and you'll say, wow, these are fascinating. They're not on the shelf at all in the supermarket or in restaurants, oftentimes.

And those, those winemakers over there, “Yeah, we sell out everything we can produce here in the winery.” So why don't you do it on larger scales? Because it well the merchant, the merchandising and the sales of, of wine is that linkage between the winery and the consumer. That's not it cintures things down instead of broadening, broadening the opportunities and choices.

And it's very hard to maintain them. And literally we are down to 15 varieties internationally that are, that make up 95% of all the wine being produced. It's sort of sad, we should, we should take advantage of that diversity and request it and demand it. And it will also allow us to adapt to climate change much more effectively.

All the tools are there. We have wine varieties that grow in every possible climate and they actually make pretty nice wine, even in very hot climates in some cases, but they have a different phenology and different cycle of bloom and ripening. They have a different tolerance of heat and they have probably different, different physiological mechanisms that allow them to cope with those situations too.

Emile: [00:22:23] Well, Kerri, thanks for that question about climate change and Andy, for your response. It makes me want to go out and see if I can find those, um, rare and unknown wines out there. And maybe when, when we're out of this COVID pandemic, we can go on some trips and see what we can find. And that tees up the next part very well.

So this concludes this part of our two episode feature on viticulture. So be sure to listen to part two, where we delve into the effects of weather and climate on viticulture and what the future might hold for the industry.

Thanks for listening to Come Rain or Shine, podcast of the USDA Southwest Climate Hub 

Sarah: [00:23:08] And the DOI Southwest Climate Adaptation Science Center. If you liked this podcast, don't forget to subscribe like or follow for more great episodes. If you want more information, have any questions for the speakers or would like to offer feedback, please visit or 

Emile: [00:23:33] Our sincere thanks to USDA Agricultural Research Service, the Sustainable Southwest Beef project, and the US Geological Survey for supporting this podcast.