By Nan McCreary
The primary role of yeast in winemaking is to convert the sugars in grape-must into alcohol and carbon dioxide. Selecting a yeast is one of the most critical decisions in the winemaking process. The yeast strain you choose will affect how quickly fermentation begins and how rapidly it progresses, as well as impact the aromas, color and character of the final product. While all winemakers use a yeast called Saccharomyces Cerevisiae, within this species are hundreds of strains designed to produce a myriad of characteristics.
To guide winemakers through the yeast selection process, The Grapevine Magazine talked with legendary Napa Valley winemaker Tom Eddy, who has been making wines since the 1970s. Eddy started his brand, Tom Eddy Winery, in 1991, and is well-known for his elegant, long-lived Napa Valley Cabernets. He also parlayed his training, experience and education at the University of California, Davis into a successful consulting business with a broad client base.
The Grapevine Magazine (GV): Next to the actual fruit, yeast selection is one of the most important elements in determining the quality and style of wine. What changes have you seen in options available to winemakers today?
Tom Eddy (TE): The technology in the microbiological aspects of winemaking has changed drastically in the last 30 to 40 years, and there have been clear and exciting transformations in the use of different yeasts. When I began my winemaking career in the 70s, there were just two types of yeasts, a Montrachet for white wine and Pasteur Red for red wine. It frustrated me that the Montrachet was sluggish, and you never knew when it was going to finish fermenting. On the other hand, the Pasteur finished really fast and often left behind residual hydrogen sulfide, which smelled like rotten eggs. We never challenged this because we’d always done it that way. We just had to adjust the temperatures and keep a close eye on fermentation. We didn’t challenge the importance of nutrients inherent in grape juice either. In other words, yeasts perform at different levels based on the availability of amino acids and other compounds, and this varies from vineyard to vineyard and season to season. We realized we needed a certain amount of fertilizer in the yeast, but we didn’t think about it to the point where we analyzed it ahead of time.
GV: In the 70s and the 80s, California entered the modern era of winemaking, and began to create wines that could compete on an international scale. Did advancements occur in the quality and availability of yeasts?
TE: Yes, in the early 80s, the industry really started to change. Microbiologists began to get creative, and suddenly, for the first time, a new yeast came out. It was called Prise de Mousse (PDM) and it was touted as a yeast that would do everything you wanted it to do: it didn’t need a lot of nitrogen, it didn’t ferment so quickly that it would foam over and create a mess, nor did it necessarily produce a lot of stinky wine. Fermentation was also very efficient, so you could turn a tank over in five to six days instead of nine or 10, which was very important in the logistics of the winery. PDM was a hot ticket for four or five years. I can remember converting everything I did to PDM in those days, but then I began to question the quality of the wines because they seemed to taste somewhat muted and had lost some of their varietal characteristics. Microbiologists that I respected came to the same conclusion. We determined that the problem was in the very efficiency that made this yeast so popular. In fact, the fermentation was so efficient that it created less heat but modified the chemical reactions in the juice that give us the wonderful fruity aromas, particularly in white wine. So suddenly the hunt is on for another yeast. Now, because of developments in global communication, technology is spreading, and European suppliers are coming to the U.S. to present products that are totally unique to the wine business. This begins the era of designer yeasts.
GV: What exactly is a designer yeast?
Microbiologists are looking at the DNA of yeasts and figuring out how they can manipulate it to produce desirable characteristics. For instance, they may like yeast “B3,” but that yeast produces hydrogen sulfide on occasion, so they manipulate the DNA to reject elemental sulfur. This guarantees that your wine will never have that stinky, rotten egg smell. Another yeast, “B4” for example, does well with Chardonnay and produces the buttery characteristics that many winemakers like. Now, this all sounds good, but once you’ve manipulated that portion of the helix, you may have changed the DNA so that it has undesirable attributes, like slow fermentation. For the first time, scientists are looking at all the issues that concern winemakers—elimination of hydrogen sulfide, control of fermentation, production of desirable aromas, even the ability to use juice that is low in nitrogen because it’s been a difficult year—to make what we call designer yeast.
GV: With so many options, what are your challenges as a winemaker?
TE: I have to decide what I want to be, what I want to achieve, and what problems I have coming into this harvest. I now have 152 yeasts to choose from, so I set up an Excel spreadsheet with 15 different characteristics that I want or don’t want. I look at the wine variety, and the growing conditions and I check boxes to decide what yeast to use with this wine, this year. Every harvest is different, and the yeasts will perform only if they have sufficient nutrients. So, a few weeks before harvest, when we’re doing normal sugar sampling and acid testing, we also run analyses on nutrients to determine levels of nitrogen, ammonia levels and amino acids. If we’re low, we could add fertilizer, but then that may cause other problems. The yeasts may get so excited that fermentation stops at a certain level, leaving me with wines that taste hot and flat with muted floral flavors. In this case, I go back to my spreadsheet and find a yeast that ferments easily with low nitrogen, and I choose that yeast.
GV: Are these wines expensive?
TE: Yes, they are expensive. Just like new drugs, it takes years and years of research to make changes in DNA, and the yeast companies need to recapture their costs. You can buy a 10-pound drum of the early yeasts —Montrachet and Pasteur— for $10 a pound. Ten pounds will take care of your entire harvest. Designer yeasts run between $40 and $60 a pound. In selecting a yeast, you have to look at your bottom line. If you’re producing 100,000 bottles of five-dollar-a-bottle wine in a 100,000-gallon tank, you have a very price-sensitive program, where two or three cents a bottle cost could make or break you. In this case, you could go back to the original Montrachet or Pasteur, or even the PDM, and it would probably be okay. On the other hand, if you’re producing a $100 bottle of wine, using a designer yeast that may add 25 cents to the bottle cost is not that significant, and could improve the quality of your wine and give you an advantage over your peers.
GV: Do you use designer yeast at your winery?
TE: We’re small —we only make 4,000 cases a year— and no, we don’t use a designer yeast for every single batch of wine. If we make 20 batches in a year and find that a certain batch will produce a certain kind of wine, a certain kind of fermentation and a certain quality level, we might use the same designer yeast for five different lots, or 30 percent of our production. By producing that much wine, we can buy yeast in 10-pound boxes instead of one-pound boxes, which is much less expensive. It’s pretty easy to calculate how much yeast you need. The industry standard is to add two pounds of yeast per one thousand gallons of juice. One pound isn’t enough to kick off fermentation, and three pounds is overkill, and the wine will ferment too fast. Because we know our vineyards and what they need, we can usually budget ahead of time for yeast, additives and some level of nitrogen.
GV: As a consultant, what types of yeast-related problems do you typically see among winemakers?
TE: A lot of winemakers believe that if you buy a yeast in a specific category, that yeast will be just what you need because all yeast today is first-rate. However, these winemakers often don’t know what’s in their juice, so they throw the kitchen sink into the mix—every fertilizer, every chemical, every additive— and cross their fingers, not knowing what the impact will be. In fact, what you’ve added can cause other problems. You can over fertilize, for example, and cause the yeast to explode to the extent that they start to die off because of high alcohol, and then some other organism takes off because of the high nitrogen and basically spoils your wine. I see this all the time. Often, I can identify the problem by interviewing the winemaker, looking at the timeline or testing for spoilage organisms. There is usually a reason for spoilage and ruined wine.
GV: Are resources available to help winemakers understand oenology so they can avoid these types of problems?
TE: Yes, many young people coming out of schools like UC Davis, Cal Poly or Fresno State are learning about the more sophisticated aspects of wine technology. They are reading more, they’re studying, and they’re listening to podcasts or participating in webinars that can answer questions related to common problems. Because of the internet, information is available quickly. It’s not like in the old days when you had to wait a week to meet your peers at a local coffee shop and exchange ideas.
GV: Tom, with all your years of experience and training, you are a virtual walking encyclopedia of the wine industry. Thank you for sharing your knowledge with The Grapevine Magazine.
TE: You’re very welcome. Anytime.
