On the Yeast Trail: Genomic Research in Vineyards
Most people appreciate a glass of wine to celebrate a special occasion, accompany a meal or just sip and savour. What they might not appreciate is the importance of one particular ingredient in the wine fermentation process, and that without it they would be left with grape juice in their glass. That special addition is yeast. Yeast is a fungus that naturally occurs on all fruit. The identification of yeast species began in the 20th century when microscopes helped scientists understand their function. The word “yeast” means “to boil” and if you observe the productive frothing and bubbling during fermentation, you can grasp the significance of yeast in converting sugar into ethanol and carbon dioxide.
It was eventually discovered that each wine growing region is inhabited by native yeasts which affect the taste and quality of the final product of the grape berry—the wine. Natural fermentation begins the moment the skin of the grape bursts open, allowing the yeast living on the grape’s skin to mingle with sugars in the flesh. Viticulturists hope that this union will result in a fine wine expressing the “terroir” or the characteristics of the region.
In the Okanagan Valley, BC, there are a few viticulturists—who manage the vines, soil condition, irrigation and pest controls—working with wine experts and scientists to identify the indigenous yeast specific to that locale so they might improve their wine’s quality and commerciality.
To Matt Dumayne, a wine maker for over 18 years, it is important to protect the growing environment and allow nature to do its job. Dumayne has experience growing in New Zealand and Oregon and settled into the Okanagan five years ago. “I have been with Okanagan Crush Pad Winery for the past three years and we are focusing on using organic practices. None of the wines we make have additives or enzymes or commercial yeasts,” Dumayne explains. “We have baby doll sheep that graze the weeds under the vines, and chickens and ducks that eat the bugs and also fertilize the soil so we don’t have to use harsh pesticides and chemicals. We worked with Alberto Antonini, a famous wine making consultant out of Italy, and he was the one who encouraged us to go organic a few years ago. It’s his philosophy that we are only on this land for a while and we have a duty to leave it in better shape than we found it.”
“If you farm commercially, the natural environment dies off in about 25 years,” Dumayne adds, “but if you’re farming organically there is no reason why the vine cannot live four to five hundred years.” Conventional grape growing practices kill off much of the natural environment, including the indigenous yeast cultures so it becomes necessary to add more commercial yeast varieties during fermentation.
A research project partly funded by Genome BC allows Dr. Vivien Measday, Associate Professor at the UBC Wine Research Centre, and her graduate student Jay Martiniuk to work with Dumayne and other growers and vintners. “We are interested in identifying the yeast populations present on the grapes in the vineyards, and specifically yeast that would be good for winemaking,” explains Dr. Measday.
Measday further explains that Saccharomyces cerevisiae (S. cerevisiae) is the “wine yeast” that can complete a fermentation, and almost all commercial strains are S. cerevisiae. In the early stages of spontaneous fermentation, the yeast population is dominated by non-Saccharomyces indigenous yeast such as Hanseniaspora uvarum, Metschinokowia pulcherrima and Candida stellata. Once the ethanol levels rise, then S. cerevisiae survives and completes the fermentation whereas the other yeast species are killed by the ethanol.
Measday works with wineries like Okanagan Crush Pad and Stoneboat Vineyards because they allow for spontaneous fermentation. “The grapes are crushed and pressed and the fermentation proceeds naturally. There is no inoculation of a starter yeast culture. This way there will be a greater variety of yeast species which may help contribute to sensory quality of the wine. We are interested in this from an industrial application and a research application because we’ve actually been able to identify S. cerevisiae that we believe is native to British Columbia from Stoneboat Vineyards.”
Measday and her team use a method called microsatellite profiling which examines a few regions in the yeast genome that provide a DNA fingerprint telling them what the yeast are and where they may have come from. Using this same method, the team also found that Okanagan Crush Pad has another Saccharomyces species (i.e. not S. cerevisiae) that is very active in their spontaneous fermentations.
“The indigenous population we have identified from Stoneboat Vineyards is an S. cerevisiae population and we are planning on doing whole genome sequencing of these strains. We are also planning on identifying the non-Saccharomyces yeast [as mentioned above] in both Okanagan Crush Pad and Stoneboat Vineyard spontaneous fermentations which also requires DNA sequencing but only a very small region of the genome,” says Measday.
“Okanagan Crush Pad really wants to showcase the terroir of their vineyards, so they want the natural yeast, but when commercial yeast has been used previously in the winery, it can be hard to eliminate,” Measday explains. “The commercial strain is usually the one that ends up carrying out the fermentations as they still exist in and around the winery and on the equipment.” If the researchers and winemakers want unadulterated natural yeast, they will have to make sure the environment is free from the stronger commercial strains. Measday recalls that in one instance the natural flora and fermentation process was overtaken by a stronger commercial species that had not been used at the winery in over seven years.
“There are markers in the genomes in yeast strains from each region and they can evolve over time depending on the climate, inputs and nutrient levels. You might see a shift in the environment and the dominant yeast will survive—it’s very dynamic,” Measday describes. “Ideally, what we would like to do is provide the wineries with their native yeast strains so they can learn about which ones are present and which are still there at the end of the fermentation. The yeast that have survived the fermentation will be the ones with more winemaking potential. Instead of using a commercial strain, which may be better suited to grapes grown in Europe, Okanagan Crush Pad and Stoneboat Vineyards can inoculate with yeast we’ve isolated from their own vineyard. We can also advise on cleaning practices so as not to expose the vines to commercial yeast.”
“So far we’ve looked at Pinot Gris grapes from Okanagan Crush Pad and Pinot Noir from Stoneboat Vineyards, but there are a lot of different grape varietals and we think the yeast on each varietal will be unique.” Measday’s team is examining if yeast populations have preferences to growing on specific grape berries and is taking samples from different varietals grown in the same vineyard to measure the differences.
Stoneboat Vineyards started out 11 years ago using primarily commercial yeasts, but Tim Martiniuk (twin brother of graduate student, Jay), is enthusiastic about the attributes expressed in their Pinot Noir. “As we learn more about spontaneous fermentation, our goal is to eventually move to one hundred percent spontaneous fermentation. We want to better understand the different yeasts that are at work during various points in the fermentation so that we can have better control.” Martiniuk agrees with Measday that spontaneous fermentation results in a more complex wine. “The wines tend to have more layers to them because there are different yeast at work and each yeast brings something different to the table. When you’re using commercial yeast, that one strain is dominant and gives certain characteristics—and that’s all you’re going to get in your finished wine.”
“This research is an important project for us because we are trying to create wines that are as true as possible to where they are growing. The beautiful thing about wine is that it expresses things like weather and soil, and having a better understanding of the yeast is just one more way we can amplify the expression of the origins of the wine,” says Martiniuk.
The goal of BC winemakers is to achieve greater distinction for wines they produce; and, if utilizing indigenous yeast is scientifically proven to help, then more focus on this type of research will be beneficial. Domestic wines will nose their way into the international market with confidence, and impress the oenophiles who will be able to recognize and describe the uniqueness of the Okanagan in each glass.
Dr. Vivien Measday may be contacted at the UBC Wine Research Centre: firstname.lastname@example.org