It's the yeast we can do

Wines & Vines, June, 1999

Genetic engineering, the transfer of genetic material from one organism to another to alter the existing gene to achieve a specific goal, such as protecting a vine against virus disease, has been much in the news recently. There are genetically-engineered potatoes, tomatoes and other plants which have caused some controversy. Critics of genetic engineering are concerned about a number of issues, including environmental contamination and a range of health hazards, including the increased chance for allergic reactions and the emergence of antibiotic-resistant bacteria.

If any one area offers scope for genetic engineering it would seem to be wine yeast, and there are reports of work being done in that area, but at this point, no one wants to come forth and discuss it. One yeast authority, who asked to speak off the record, said flatly: "No one wants to have anything to do with genetic engineering."

Greg Fowler, in charge of winemaking for Seagram's Fine Wines in Napa, said that from a winemaking point of view, experiments and advances in clonal selections, for example, were of much more importance than genetic engineering.

So what are the major wine yeast issues? We asked Ralph Kunkee at U.C., Davis for a quick cheat sheet. Kunkee listed three basic concerns:

* Whether to add wine yeast or not? If not, what conditions are required? If so, which strain of yeast?

* Importance of new wine yeast strains for increased ethanol tolerance, increased flavor and odor components.

* Importance of development and application of new taxonomic procedures for positive identification of wine yeast strains.

David Ramey, winemaker at Rudd Estate, chooses not to inoculate with commercial yeast most of the time. "I started doing experiments at Chalk Hill in 1990 with control comparisons. I put the juice in four different tanks, inoculating three tanks with three different commercial yeasts, and left one tank alone. Ultimately I had 30 experiments and was convinced that going with natural yeast was right to do unless there is a good reason not to."

According to Ramey, the main reason to inoculate is stuck fermentation. "Sometimes juice from older Chardonnay vineyards with phylloxera damage have difficulty completing fermentation. Then I use a commercial yeast."

Occasionally Cabernet Sauvignon from soils with poor nutrition were also difficult to ferment dry on native yeast. "If I know the vineyard, I'll start out with a commercial yeast. If I start with a native yeast, then see the fermentation starting to slow down, I can jump on it quickly with a commercial yeast."

What does Ramey see as the advantages of native or wild yeast fermentation?

"What I consistently see is a more complex aroma with better integration of oak character. The wine also seems softer and plusher on the palate while commercial yeast seems more lean. I also found lower phenolics in native yeast. Maybe because native yeast fermentation takes longer, you get a 'yeast fining' effect," Ramey said.

How does Ramey account for the presence of native or wild yeast?

"I know that many people claim they don't exist in the wild but are found from yeast already present in the winery. The problem I have with that is that I know of new wineries where the first crop in for the year, using all new equipment, the wine will ferment, both red and white. In the end, I'm a practitioner, not a scientist. I don't need to know exactly how it happens. Just that it works."

Ramey said there was also a striking difference between native yeast and commercial yeast under a microscope. "Commercial yeast are larger, more uniform in shape. They basically all look the same. Native yeast really look different. They are a hodgepodge."

Don Blackburn, winemaker at Byington Winery in the Santa Cruz mountains has run yeast experiments for several years, looking for impact on flavor and aroma.

"Different yeast strains tend to ferment at different temperatures, which has an impact on flavor and aroma. Also, different yeast tends to have different behavior toward the end of fermentation, when yeast has to work harder because of accumulation of waste products."

Blackburn said that although having a yeast that would finish the wine dry was a goal, he has also found that the more powerful yeasts did not always give the best results as far as flavor was concerned.

What does Blackburn look for in general in a wine yeast? "For a red wine, I want a yeast that can survive temperatures of between 95 to 100 [degrees] F without 'kicking the bucket.' I also want a yeast that won't produce reductive odors. For white wines, the yeast should keep going at lower temperatures."

Changes in Pennsylvania

Pennsylvania has three new wineries and ownership in two others has changed hands, according to the "Pennsylvania Wine Traveler," published by the Pennsylvania Wine Association.

Manatawny Creek Winery is located at 227 Levengood Rd., Douglassville, Pa. 19518. The fax is (610) 689-9804 and the e-mail is manatawny@aol.com.

Galen Glen Vineyard is on Road #1, Box 82-1, Andreas, Pa. 18211. The phone is (717) 386-3682.