For some producers, the answer is both. The use of proprietary yeast, which stems from indigenous strains, is a growing trend that proponents say helps ensure a smooth vinification process. Yeast also serves a stylistic purpose: many winemakers believe wines offer their ultimate expression of terroir when inoculated with these special yeasts.
Commercial versus native yeasts
Commercial yeasts have their advantages, mainly that they ensure wine avoids undesirable elements, such as acetic acid, hydrogen sulfide and excess acetaldehyde-and they see fermentation all the way through. In addition, it's easier to add yeast from a package rather than wait for spontaneous fermentation to commence or nurture a pied de cuve. Certain yeasts can even be used to bring out desired aromas, flavors and textures. However, detractors of commercial yeast say the resulting wines aren't as vibrant and can lack personality-it's a big reason why natural winemakers opt for the latter. It could mean that, for some, proprietary yeast may be the best of both worlds.
The Cerro Chapeu winery was founded in 1973 in Rivera, Uruguay by Quico Carrau Pujol, who came from a long line of winemakers in the Penedes. His son, Francisco Carrau, joined the winery in 1981. As a doctor in chemistry with a focus on yeast, Francisco quickly turned his attention to the role yeast played in vinification. In 1985, he started conducting research into native yeasts in his own vineyard.
"At that time there was very little commercial yeast available," said Carrau. "We didn't have contamination of commercial yeasts in the winery," which was advantageous to his research project. Yeast is a tricky beast: it easily makes its home in tanks, pumps, tubes... pretty much everywhere. Because Cerro Chapeu had done several vintages solely by spontaneous fermentation, Francisco had pure samples to work with.
He believes that, on average, only about 10% of native yeast is truly viable, and quality strains vary from year to year. The other 90% might not produce concentrated or pure flavors or might be susceptible to acetic acid bacteria, resulting in wine with vinegar notes.
Despite the small pool, Carrau is adamant that native yeasts provide more concentration in the nose and on the palate, especially compared to commercial yeasts. Those, for the most part, require the addition of nitrogen, which mutes a wine's character, according to Carrau.
To find the optimal yeasts, Carrau takes samples from the vineyard every February or March, then does a vinification with the strains, looking primarily at flavor and aroma intensity.
Despite the complex nature of yeast, Carrau's screening process for quality microbes is fairly rudimentary: three human tasters assess the samples organoleptically. "The complex analysis is more in the mind than the equipment," he cautioned. If a sample passes muster, the strain is preserved, and a pied de cuve is created during the following harvest to test it further.
Prior to 1995, Cerro Chapeu only focused on saccharomyces cerevisiae, a brewer yeast used for all types of fermentation-from bread starters to beer-that is very common in vinification. But in 1995, Carrau and colleagues started a project with the University of Uruguay, where Carrau was a professor, to explore non-saccharomyces, such as Hanseniaspora uvarum, which presented naturally in the vineyard. Not only did they show levels of resistance to diseases, but several of these strains positively influenced wine flavors and aromas.
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