A recent study conducted in New Zealand could explain the source of New Zealand and Napa Valley’s one-of-a-kind terroir flavors.1 Terroir characteristics in wine have little to do with minerals in the soil, and everything to do with the yeast strain S. cerevisiae, according to this study. Certain strains of this yeast, which seem to dramatically affect the aromatics of a wine, occur naturally in environments around New Zealand and Napa Valley. This could help explain why the use of commercial yeasts has been said to ruin the natural flavors of a terroir. Using this knowledge, producers in Napa Valley and other regions have the potential to develop better wines by choosing a strain of yeast that emphasizes certain flavors.
Pinpointing New Zealand’s Terroir
For the study, researchers observed the fermentation process on six terroirs in New Zealand, including Marlborough, Hawke’s Bay, Nelson, Wairau Valley, Awatere Valley, and Central Otago. They isolated 295 strains of yeast that occur naturally in these regions. In order to narrow down this list to just those strains that contribute significantly to aromas in the wine, researchers used a commercial batch of Sauvignon Blanc from Marlborough as a control, and fermented the grape juice using each of the strains. Some of the strains failed to ferment the wine at all, and were taken out of the study, leaving 112 possible culprits.
Researchers tested the aromatics on the resulting batches, and found yeast strains that produced aromatics closely matching the characteristic aromatics found in each of the six terroirs. When they added these terroir-specific strains to grapes grown outside of their natural terroirs, they discovered a strong correlation with the aromatics found in grapes grown in their natural terroirs. In other words, despite being grown in Marlborough, some grapes expressed characteristics of those grown in Central Otago when they were given the Central Otago yeast strain during fermentation. Presumably, a similar method could be used anywhere in the world, including areas ripe with yeast experimentation, such as Napa Valley.
Growing a New Grand Cru in Napa Valley
In the past, winemakers believed that the key to Napa Valley terroir was the porous soil and hot, dry climate. While the environment does contribute to the characteristics of grapes grown on Napa estates, this new study shows that soil and climate are likely not the only factors that shape Napa wine. Many modern Napa growers rely on commercial yeast to produce their wines, and, in light of this study, producers can now use this technique without sacrificing the essential flavors of their terroirs. In theory, a producer could pinpoint the type of aroma or flavor they want to enhance in a wine, and use a wine yeast strain that is known to produce those qualities.
A separate study from UC Davis found that, like New Zealand, Napa Valley has naturally-occurring yeast strains such as Saccharomyces, which likely come from the trees that grow around many of the region’s most popular estates. This strain of yeast is rare in healthy grapes, but exists in high concentrations on ultraviolet-damaged grapes. Due to Napa’s ample, UV-producing sunshine, the strain is most prevalent in this terroir. The strain also does not tolerate high acidity, meaning that it prefers grapes exposed to plenty of sunlight throughout the summer.
Despite the excessive sun, the strain can produce a wine with a balance of flavors, rather than the flabby, low-acid characteristics you would expect from such sun-drenched grapes. An excellent example of this can be found in vintages from Harlan. The Maiden is known for having full flavors that don’t sacrifice acidity, even after hot, sunny seasons. While researchers are still trying to determine how exactly this strain of yeast is able to affect the flavor of wine, and in what ways, they have found that wines from premium estates lose characteristics of terroir during aging. This might be due to the fact that the impact of the yeast decreases over time as the wine matures. For Napa Valley collectors who want the strongest terroir-based tastes and aromas, investing in wines that allow terroir-specific wine yeast to express itself fully in a wine’s youth is the best option.
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