Going wild: wild yeast in winemaking

Wines & Vines, Sept, 1997 by Jordan P. Ross

Alan Tenscher, senior winemaker at Franciscan Vineyards, comments: "I see a trend toward a more natural way of making wine which starts in the vineyard with organic grape-growing and extends to minimal handling of the wine. The use of wild yeast, from one perspective, puts one in that same camp. But on the other hand, there is a group of winemakers out there who are looking for any technique that will help improve wine quality. The use of wild yeast is a tool to create complexity."

The trend Tenscher observes has been popularized by influential wine critics who are proponents of wines made with more natural, less interventionist techniques. Indigenous yeast fermentations fall into this category because the vineyard's native yeast start the fermentation naturally in contrast to the common California, and in recent years European, practice of adding yeast to start the fermentation.

Fining and filtration are other examples of "interventionist" techniques which these critics object to because they perceive them as excessive manipulation which compromises wine quality. This view is contradicted by assertions from top California winemakers that a properly carried out fining or filtration can improve the quality of some wines. Nonetheless, the success Robert Parker - a skilled writer and passionate advocate of wine quality - has had in molding consumer opinions and buying habits has reached the point where some winemakers - well aware that favorable Parker reviews sell wine - are actually shaping their wines to suit his taste. This is where John Williams, owner and winemaker of Frog's Leap, draws the line: "When I see people making good wines change what they've believed in for a long time just to satisfy the latest craze, I have to scratch my head." Another outgrowth of the traditional methods "fashion", is the familiar winemaker refrain that, 'I never fine/filter/inoculate', when in private, many - including some of Burgundy's most highly-regarded producers - admit to the use of these practices. What role, then, should the wine writer have in the winery? Williams sees a limited role, "wine writers do have a place in the cellar - reflecting on and communicating the vision of the winemaker. To me, the most interesting wines are those made with conviction based on the personal experiences of the winemaker. That conviction can change, that's how wines get better, but it should not shift with the wind."

But most winemakers using wild yeast are looking less at the marketing dividends this approach pays and more at the potential for enhancing wine quality. This article will compare wild yeast fermentations with inoculated fermentations, how each affects quality and why some of California's top winemakers use wild yeast and others do not.

Inoculated Fermentation

Fermentation is a vitally important stage in winemaking. The yeast not only convert sugar to ethanol but also produce esters and other compounds which contribute to the wine's flavor and aroma. Extraction of flavor and color from the grapeskins (for red wines) also occurs during fermentation. For larger production, less expensive wines, a yeast strain is chosen to get the job done as expediently as possible - converting all of the sugar to ethanol and freeing up the tank for the next load of crushed grapes. Some yeasts produce a heavier sediment which settles more quickly after fermentation, making racking and clarification easier. For smaller production, fine wine, varying the yeast strain as well as the temperature and duration (maceration) of fermentation can enhance the wine's aromatic and flavor characteristics.

The common practice in California is to add a sufficiently large dose of a single strain of yeast (Saccharomyces cerevisiae) to the grape juice to start the fermentation. A few commonly-used strains are Prise de Mousse, Montrachet and Champagne. The yeast is selected for its ability to quickly (in a few hours) start the fermentation and to tolerate the increasing ethanol levels enabling it to ferment all of the sugar while hopefully producing minimal amounts of undesirable by-products such as volatile acidity and sulfides. Volatile acidity is acetic acid or vinegar. Sulfides are compounds which at threshold levels may be desirable but in higher concentrations smell like rubber or rotten eggs (hydrogen sulfide) or worse. Inoculated fermentations can, in certain circumstances, produce objectionable amounts of volatile acidity and/ or sulfides and, even worse, "stuck" fermentations. Winemakers get very nervous if for some reason the fermentation stops or "sticks" before all the sugar has been consumed. Stuck fermentations are difficult to restart and dangerous because once the yeast stops growing, the protective layer of carbon dioxide is removed. The door is open for spoilage yeast and bacteria (Brettanomyces, lactobacillus and acetobacter) to consume the remaining sugar, in turn producing vinegar, earthy, barnyard or sauerkraut aromas.

Wild Yeast Or Uninoculated Fermentation