While genetically engineered vines and grapes are still in the experimental stages, genetically modified yeasts are now being sold for use in winemaking, with no labeling requirements to inform consumers.

Wine can be made from grapes alone, fermented with the naturally occurring yeasts. However most wines are made with commercial yeasts and vintners have been able to choose from a spectrum of yeasts cross-bred for desired characteristics, such as the ability to affect a wine’s color or taste, the speed of fermentation or the ability to tolerate cold temperatures.

Now two genetically engineered yeasts are on the market: ML01 and ECMo01.

ML01 prompts a speedier secondary, or malolactic, fermentation process, commonly used to encourage a buttery richness in the flavor of chardonnay and several other varieties. It produces in the wine a reduction of amines, which can trigger migraine headaches and allergic reactions in some people.

ECMo01 is said to reduce in wine the presence of urethane, a suspected carcinogen in humans.

However, critics argue that these GMOs have not been sufficiently studied. Inserting genes changes the yeast's metabolism and can result in production of unexpected and possibly toxic compounds, and further testing is required to protect human health, according to GMO critics.

No local winemakers have stepped forward to claim use of GE yeasts, although there is no incentive to disclose such information in a consumer climate that is generally negative toward GMOs. In 2006, the Sacramento Bee quoted a distributor of yeasts as saying some GMO wines from California are already on the market.

The European Union requires labeling of food and beverages with GMO content, but the U.S. does not impose a similar requirement on producers.

Genetically engineered wine yeasts also pose a risk of contaminating the environment, according to PINA spokesperson Erica Martenson.

“Studies have shown that yeast survives fermentation and is not completely filtered out,” Martenson said, adding that typical vineyard practices such as recycling grapeskins and other wine byproducts back into vineyard soils could lead to the spread of GMOs.

“The grape pomace, which contains the yeast, is sometimes spread throughout the vineyards to put nutrients back into the soil. If the pomace contains GMOs, it would contaminate the vineyard. These yeasts are living, reproducing organisms.”

Some wine industry members question the value of the GE yeasts.

“Our winery is not likely to adopt GE yeasts because we don’t want association with GMOs,” said Jon Marc Chappellet of Chappellet Winery and Vineyards. “We’ve looked closely at the risks and benefits, and don’t see any meaningful advantage to genetically engineered yeasts, especially since there’s no qualitative improvement in the wine.”