Getting a Handle on Yeast

- 18 Apr '12 - 09:56

http://www.winebusiness.com/winemaking/webarticle.cfm?dataId=43875

With so many different yeasts available, our panel helps to decipher the new strains, what to look for when you buy, and whether to go commercial or native.

By Lance Cutler

From Wine Business Monthly, 07/15/2006

Take some time to look through the yeast section of a catalog from your friendly supplier and you will find page after page of specialty yeasts. According to the claims, there are strains that ferment slowly, other strains that ferment rapidly and strains that are low-foaming. There are yeasts that tolerate high alcohol, yeasts for early release wines and yeasts for residual sugar wines. You can buy yeasts that enhance fruity/floral aromas, stabilize color or contribute to mouthfeel.

Often, reading the descriptions of the various yeasts and the claims attributed to them, one gets the feeling that you don't need a winemaker at all. Simply select the right yeast for the variety and style you desire, and voila, the wine will be ready to bottle. Those of us who make wine for a living know that it is not quite that easy.

We decided to bring some experts together for a roundtable discussion about yeast. We wanted to know what was true and what wasn't about the claims made in the catalogs. Our participants were opinionated, and this led to lively exchanges in response to my questions.

Michael Terrien is currently the winemaker at Hanzell Vineyards in Sonoma, a position he's held since January 2005. Previously, he was winemaker at Acacia in Carneros from 1996-2004. Originally from Maine, he graduated from UC Davis.

Larry Biagi is a native San Franciscan and UC Davis graduate. He started in wine production and served as winemaker at Pedroncelli, Geyser Peakand Trentadue. He presently is senior winemaker for American Tartaric Products.

Peter Anderson graduated from the University of Wisconsin and went into the dairy business, which led to the wine business. He was production manager at Beringer in the 1970s through 1982. From there he moved toScott Laboratories where he has served as a sales representative specializing in fermentation products.

What has changed the most about yeast usage in the last 10 years?

Peter: I think the variety of strains. What people were looking for in native yeast fermentations is what we are trying to meet by providing all these different strains. For instance, there are a number of wineries that will ferment the same wine in separate lots using different strains. Then they blend them together post-fermentation. You can definitely tell the difference between the strains; and when you blend them together, you get something that is unique.

Larry: I think people are looking for a certain something. They might want a tropical fruit in their Sauvignon Blanc, and they're going to experiment with it. So we find the biggest difference is that winemakers are looking for something special, and they want yeast that emphasizes that specific thing in that specific wine. We have three different lines of yeast and a total of close to 50 different strains. These high-end commercial yeasts have these special characteristics, and they still will finish the fermentation. Some people use different yeast at different points in the fermentation. They call it "cocktailing" yeasts.

Michael: Over the years I've used manufactured yeast as well as native yeast. One motive for not inoculating is cost; it's not an important motive with many wineries. But if you are talking about a larger production, it's like not having to hire an extra person to inoculate all of the barrels in a 3,000-barrel Chardonnay production. And I say Chardonnay because I'm confident I can get any quantity of Chardonnay dry without inoculating. It's very forgiving of the process with little risk when you are not inoculating. With red wines there are more concerns about contaminants and bacteria. The motivation for inoculating may have more to do with decreasing your risks.

Larry: I agree that Chardonnay would be the easiest one; but as a supplier, we've seen many, many stuck fermentations on Chardonnays using indigenous yeast. There was one two years ago that was 120,000 barrels. So if there's a problem, it's a big problem. Some costs can be high; but if you figure the cost of yeast down to cents per gallon, it wouldn't be a factor in my winemaking choice. What would be a factor would be what do I get out of it and do I get it to go dry if I want it to go dry.

Peter: We had a large winery that ordered a pallet and a half of Prise de Mousse one year, in the middle of harvest, and you knew right away what that was for. So, it does happen.

Michael: As a winemaker, I've had vintages of stuck Chardonnay using inoculated yeast. We can all toss back our horror stories to one another; but since we are not scientists and can't see the bigger picture, we don't really know how many uninoculated fermentations don't finish versus how many inoculated fermentations don't finish. It's all anecdotal.

What do you look for when you buy commercial yeast?

Michael: The first requirement would be that it finishes. Whether it produces a wine with good flavors or not, I have a certain amount of skepticism that the different yeasts produce a long-lasting difference in the wine. I know Brettanomyces yeast can affect the flavor; but when I go to the store and buy the different yeasts, I'm not sure the differences described are actually due to the yeast instead of a multitude of other variables.

Larry: I would disagree. I have seen the same wine from the same vineyard come out with different flavors just because of the different yeast. Yeast is way up there as a factor on aromas and flavors. It can make a wine taste completely different.

Michael: When you are making a wine that's supposed to be drunk in a decade or two decades, does that make a difference?

Peter: I think that back in the 1970s Davis thought that yeast made a difference, but that it disappeared in the bottle over time. We've run a number of trials that prove differently. The first one I remember was at Zaca Mesa. We used three different strains, and we kept them separate over four years. We tasted them every year, and you could taste the difference even after four years. I was skeptical about it too but not now.

Michael: From the armchair it does look like there are differences. I mean, there are differences between you and me and there are differences in other living creatures, so why not yeast? Considering the bigger picture, I have to wonder which variables are most important. According to the catalogs, you can design your winemaking with descriptions of these yeasts, but that's a very small part of the picture. It has to do with the culture of your winemaking: the place, the people and perhaps the resident yeast.

Larry: Every grape is different, and every grape reacts differently with every yeast. If I was a winemaker and I wasn't happy with what I was getting from my current yeast, then I'd take two barrels or three barrels of Chardonnay and I'd experiment; and then next year if there was something I really liked, I'd go to that yeast.

Michael: I'm a reductionist winemaker in that I try to be empirical about it. I'm pretty skeptical about anything not published in the peer-reviewed literature. I have a question about the claims made by the yeast companies regarding contributions of a particular yeast, whether it's tropical fruit or deeper color. What sort of research has gone into proving that these particular yeasts have the ability to bring out these traits in the wine?

Peter: For example, we've got studies from universities where you can track increases in polysaccharide production. Whether that translates exactly, I don't know, but it's a reference point. Say you take a base point on one yeast strain, and you see a fairly straight line, but you take a couple of other strains and you'll see an increase in polysaccharides. So it's measurable data. It's not all anecdotal.

Larry: They're measurable, but they are all subjective results. Yeast manufacturers make claims to color stability and intensity. You can measure the excellular polysaccharides but is that going to give you more color? Maybe, maybe not. It depends on the grapes. You have to experiment with them.

Peter: Yeast is one tool. Obviously, there are so many parameters in winemaking. Like my old boss said, "Get good grapes and don't screw it up." What you do in the vineyards is a big deal. Which yeast you use during fermentation is another factor. It's a contributing factor: maybe not a huge one but it definitely makes a difference.

Larry: Yeast can very much affect the taste of the wine. Very, very significantly. There are so many variables. With the Montrachet you have 10 manufacturers that make that strain, but it's not the same from each one. If you try it on one grape, it works one way. Try it on another grape and it works another way.

How has the way yeast is bought and used changed?

Peter: In the past, all a winemaker wanted was a yeast that would get the wine dry. Especially in a large winery, you want to get that fermenter done and out because you're under pressure to move as fast as you can. I think that's the biggest single change in the last 15 years. People are looking at yeast strains to contribute to the complexity and quality of the wine rather than just fermentation kinetics.

Larry: The only thing we can promise you is that if you look in the catalog and you want a yeast that will finish the fermentation, we can give you something that's tolerant up to 90 degrees and 19 percent alcohol. But when it comes down to a certain flavor, aroma or color, you can't just look in the book and say this one is going to make my Sauvignon Blanc smell like pineapple. You have to try it.

Michael: It creates doubt in my mind. When I have a respected yeast manufacturer or representative telling me as a winemaker that if I add this yeast it will create these flavors, that's where I end up feeling doubtful about what you are representing.

Larry: I don't think there's a lot of deceptiveness here. When they sell you a yeast...

Peter: They say it tends to do this or tends to...

Michael: It'd be better if they said it did it with this Sauvignon Blanc fermented at this temperature on this day; but to make the generalization is at best misleading. For me as a winemaker, these descriptions of what a particular yeast might do are irrelevant. It simply has to do with my experience. As you've been saying, it's about the variables in your particular situation.

Larry: But as far as making a difference, in my opinion, yeast makes a huge difference, or can in flavor and taste.

Peter: They can make a difference, but I don't know about huge.

Michael: If you inoculate with Brettanomyces, it's huge.

How is the yeast that we buy as winemakers made and how do they propagate the individual strains?

Larry: My understanding is that you clone a strain and then you reproduce it, and most of it is sold in freeze-dried form.

Peter: They'll find all these strains in a certain region: the first breakdown is alcohol tolerance; second will be the killer factor: does it dominate a fermentation. Then you get down to the esoterics as far as, is it producing good wine. For example, we work with the ICV group in Cotes du Rhône. They'll isolate these strains starting with hundreds of different strains and reducing that to 50 and then 20. They'll do small fermentations and then break that down again. All of our strains come from specific winemaking regions around the world.

Larry: We represent three strains of Montrachet, which is a Davis, California strain. We have one called SC22. It's a Montrachet strain, but it is not going to be identical to the Red Star Montrachet that we sell or to Lallemands Montrachet. They are not exactly identical.

Peter: They take everything that comes from a certain wine region and try to isolate the different strains. Then they break those down into the most efficient. Certain strains won't handle the alcohol. Others can't compete with the other strains.

Larry: They also look at cells per gram. A typical production yeast will be 20 to 40 billion cells per gram. That's why you use manufactured yeast because you have this high count of what you are trying to get. They each have their different characteristics. A winemaker may want a particular characteristic for a particular wine. If you use indigenous yeast, it's not as reproductive or consistent and there may not be as many cells. It's sort of Russian Roulette.

What are some of the more interesting new strains?

Larry: We now have one yeast called A3 from AEB that helps finish malic fermentation because it doesn't consume the malic acid. Therefore, at the end of fermentation the malic acid is higher, which in theory will make your malolactic go easier. It will produce less alcohol because the conversion number is lower. Basically, if you had a wine that normally would end at 13 percent alcohol, this yeast would give you closer to 12 percent. It's pretty significant.

Michael: When my fermentations are stuck, I get Saccharomyces bayanus yeast to finish them.

Larry: That's what a lot of people do. The way we handle that is to have a set of different formulas for stuck fermentations. We would ask you what's the residual sugar? What's the current alcohol? What's the current pH and total acid? From that we would choose the formula that applies.

Typically you'd add a bit of water and a bit of concentrate to a small percentage of the mass. You add some nutrients and the total amount of yeast that you need for the whole tank into this small batch; and when that drops 50 percent, you put it into the big tank. Then we add some different nutrients, so it's a two-step process. No matter the formula, we also use the same yeast. Ours is called BCS 103.

Peter: We do a similar kind of deal. We isolated a strain with very good high-alcohol tolerance called Unaferm 43.

What is encapsulated yeast and what are its uses?

Peter: It's an alginate coating on the yeast. It's like a giant tea bag that you put into a fermenter. It's touted for making wines with residual sugar and can be used to restart stuck fermentations.

What are the advantages of using native yeast?

Michael: First, the term "native yeast" is used a little liberally and is misleading, too. Anybody fermenting in a custom-crush facility is probably just using a lower inoculum of somebody else's yeast rather than native yeast. It's clear from the research I've read that a new winery doesn't have much of a population of yeast capable of fermenting juice to dryness. But then in an established winery, there's some resident population of yeast that can do it.

So if I make an uninoculated Chardonnay in a facility in which we are making Pinot Noir, with the help of commercial yeast, it might be that in fact we are inadvertently inoculating the Chardonnay with that yeast, albeit at a lower dose.

That being said, why are you using native yeast? Why not just buy commercial yeast and add it?

Michael: There's no risk, and I like the results.

Peter: There's no risk?

Michael: At least in my experience the risk is no higher than with inoculated Chardonnay. I've seen inoculated Chardonnays stick as well as uninoculated Chardonnays, and I know how to fix both. And your recipes are very helpful to winemakers.

arry: Would you say it gives a taste or flavor specific to that vineyard?

Michael: No.

Peter: I know people who seek the middle ground. They will break it down into three portions where one will be native fermentation and the other two will be a couple strains that they like. So they don't have to worry about the ramifications of an entire fermentation going south.

Larry: As a winemaker, I've never used indigenous yeast for a fermentation. My thinking of why you would use indigenous yeast is that all yeast originally is created from a certain area. So if you thought a particular vineyard had a specific character or identity, that would be a major reason for trying it.

But there are a lot of arguments against it. It's not going to give the same results every year. And I really believe that if you use commercial yeast correctly, then you will have a lot fewer stuck fermentations than using native yeast. That's just my opinion.

Peter: If you use native yeast, then you're hoping that a certain strain out there dominates the fermentation. You're hoping. If I was a commercial winemaker, I'd like to avoid the risk.

If you have a small vineyard and you're making wine just from that vineyard, maybe native yeast will contribute to the specific terroir. But that's a luxury few people have.

If you are making 500,000 cases, then you have a lot of restrictions as far as how quickly you need to get the wine fermented. At least with a commercial strain you have someone to blame.

Larry: You're hoping you have enough cells to dominate the fermentation, and any commercial yeast has between 20 and 40 billion cells per gram. That's a tremendous number and, in theory, should never fail, but it can.

Michael: Do you accept responsibility for stuck fermentations?

Larry: Nobody accepts responsibility for stuck fermentations because there are too many variables. Did the guy turn the jacket on and forget to turn it off and freeze his tank? Did he put in 300 parts of SO2?

Michael: I was reading some material by Brad Webb who was talking about two disastrous vintages in 1933 and 1934. It was Brad's observation that there were no yeasts around capable of taking the fermentation to dryness in those first vintages after Prohibition. So the research universities developed yeasts to finish fermentation, and that was their main motivation. More recently we have this soul searching need to find meaning in wine beyond simply this industrial process.

Larry: In 1933 you had red wine and white wine. You didn't have Syrah, Pinot Noir and Riesling. You didn't have varieties that were supposed to taste like apples or pineapple or raspberry. Specialty yeasts can enhance those flavors.

Michael: My yeast choice is not necessarily about varietal expression so much as I'm looking for mouthfeel or aromatic flavor or complexity.

Larry: The main questions I get are, "Is the yeast temperature-tolerant," and they'll give me a range. "Alcohol-tolerant," and they'll give me a range. Then they say, "My wine has these characteristics, and I'd like more emphasis towards that."

Peter: The customers are looking for complexity through commercial strains. They're looking for that complexity while at the same time having yeast that will complete fermentations.

What is the most important single yeast trait?

Larry: Finish fermentation.

Michael: The most important thing about a barrel is that it holds the wine.

Peter: That's basic. It's got to finish if you are looking for a dry wine. After that, it would be contributing complexity and mouthfeel of some sort.

With your long-time customers, are changes in yeast protocol suggested by you or are they requested by your customers?

Peter: A lot of the feedback comes from the customer. They experiment with different strains, and they get excited. They want us to taste the experimental barrels. They allow us to take barrel samples out to other customers because they are excited by what they see. Winemakers are always looking to make better wine, so they're willing to experiment with different strains.

Michael: That's where I part company. Yeah, we always want to make wine better, but I certainly wouldn't look at yeast to do that. Start tinkering with the bigger variables, like how much you're irrigating your vineyards or pulling leaves or what barrels you're using because, certainly, the oak can flavor a wine a lot more than the yeast.

Peter: There are all these parameters in winemaking. It's one tool. It's not the be-all-end-all, but it's another tool you have out there.

How critical are nutrients?

Michael: Nutrients put flavor in the wine.

Peter: We find it makes a lot of difference when you add the nutrients. If you add them at the beginning, then you are feeding everything, including the indigenous strains brought in on the grapes. It tends to be more effective at one-third sugar depletion and using several additions. It's one thing we've learned over time.

Larry: At the end of fermentation you have all of these toxic dead yeast cells at the bottom of the tank. They prevent things from fermenting. Toward the end of fermentation, nutrients are depleted. Nowadays everybody takes their juice and analyzes it to determine additions. In our stuck fermentation formulas there is at least a two-nutrient addition.

Winemakers often have a tendency to use too much of a good thing. What are some of the more egregious errors made with nutrients?

Larry: Standard additions, like using so many pounds per thousand of Superfood just because.

Peter: Yeah, without even seeing what you actually need. And additions of DAP because that's more like candy than a complete food source.

Michael: I make Chardonnay and Pinot Noir, and these varietals are usually stocked pretty well with nitrogen. I don't tailor my nutrient additions to the must. I find a lot of wines are compromised by nutrient additions. I think probably of the two, yeast and nutrients, the more dominant flavors come from the nutrients.

•

Many years ago I was interviewing Brad Webb, the legendary winemaker from Hanzell Vineyards and Freemark Abbey. He told me, "There was a time when I felt guilty because yeast works 168 hours a week, and I was only working 40 to 60 hours a week. I thought the least a winemaker could do would be to work as hard as the yeast."

Clearly, there would be no such beverage as wine without yeast and its ability to ferment. After listening to the experts in our roundtable, I'm pretty sure that certain yeasts are capable of contributing specific characteristics to wines in special circumstances, but every vineyard, fermentation and wine is different. It's the multitude of variables that make wine and winemaking so fascinating.

I think it behooves winemakers to experiment by using the various yeast strains on their own grapes and then make judgments based on our own experience. Just be glad that the yeast is working for you and that there is no "yeast union." wbm

Lance Cutler

Lance Cutler is the winemaker for Relentless Vineyards and the author ofThe Tequila Lover's Guide to Mexico and Mezcal, Making Wine at Home the Professional Way and the Jake Lorenzo books (www.winepatrol.com).

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Extrait :

That being said, why are you using native yeast? Why not just buy commercial yeast and add it?

Peter: If you use native yeast, then you're hoping that a certain strain out there dominates the fermentation. You're hoping. If I was a commercial winemaker, I'd like to avoid the risk.

If you have a small vineyard and you're making wine just from that vineyard, maybe native yeast will contribute to the specific terroir. But that's a luxury few people have.

If you are making 500,000 cases, then you have a lot of restrictions as far as how quickly you need to get the wine fermented. At least with a commercial strain you have someone to blame.

Extrait :

With your long-time customers, are changes in yeast protocol suggested by you or are they requested by your customers?

http://www.nextmags.com/gratin/how-to-handle-so-many-different-yeasts

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