Ask the Master of Wine:
"What are the issues facing winemakers in choosing between natural fermentation and adding commercial yeast? Does it really make a difference in the final product?"  (December 17, 2002)

Wine & Spirits magazine has been running a series of articles by North American Masters of Wine. The editor/publisher, Joshua Greene, has graciously allowed me to reprint these Q & A pieces.

"What are the issues facing winemakers in choosing between natural fermentation and adding commercial yeast? Does it really make a difference in the final product?" – Eric Sklar

	Sandy Block is General Manager of Whitehall Imports, and vice president and founding board member of the Institute of Masters of Wine, North America.

Sandy Block, M.W., replies:

Commercially prepared yeasts are often cited as one of the chief factors in the homogenization of wine styles throughout the world. Some critics contend that only natural ambient yeast populations, with their longer fermentation cycles, can make wines that preserve the unique character of their vineyard origins. Many of Europe's classically trained winemakers follow this traditional practice. But most quality-oriented enologists in the New World routinely inoculate to ensure reliable fermentations.

There are many reasons for choosing one technique over another. First, a "natural" fermentation requires a sufficiently concentrated yeast population in a vineyard or winery to ensure that vinification proceeds successfully. Ambient yeasts act more slowly, which may help increase aromatic complexity and flavor extraction, but they also expose unfermented juice to the risk of bacterial spoilage; that's problematic in cold climates, where it's hard to start fermentations naturally.

Cultured yeasts, on the other hand, act faster and eliminate the risk of spoilage. They also confer greater control, permitting enologists to sculpt wine to exact specifications. For instance, some wild, naturally occurring yeasts contribute off-putting aromas and need to be disabled to produce a clean wine; some wine styles, such as Champagne, require enologists to use cultures selected for unique characteristics (granularity, or ability to ferment at cool temperatures, for example).

Research suggests that in conditions supporting ambient yeast fermentation, use of inoculated cultures may produce wine with subtly different characteristics: lower in volatile acidity, analytically drier, less integrated with the oak in which it's aged. As to whether you can you taste the difference, it's hard to say whether the supposed increase in aromatic complexity and the softer textures of a wine fermented with natural yeasts are consistently measurable. Certainly, if you're talking about heavily processed, killer-yeast fermented wines versus delicately handled wines whose fermentation is "natural" as part of an overall winemaking protocal that respects the fruit, there's a big difference. But as you head in from those extremes, things become less clear-cut.

What is clear, though, is that defining the issue in terms of "natural" fermentation versus "commercial" yeasts is misleading. The terminology implies two approaches to making wine: one artisanal and in harmony with the biological rhythms of the soil, the other industrial and product design-driven.

This is putting the cart before the horse. The goal of any winemaker is to create a delicious wine. If achieving this involves use of natural yeasts, that's justification enough. But inoculation is sometimes not only warranted, it's the only logical choice. Ultimately the proof is in the glass: how does it taste to you?