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The Dangers of Genetically Modified Yeast Wine

Despite the Wine Institute’s recent statement that no genetically modified organisms (GMOs) should be used in winemaking, the Sacramento Bee recently reported that, according to American Tartaric Products, the first wines made with a genetically modified wine yeast, ML01, will be released this year.

This yeast is available only in North America where GMOs are unregulated. It was modified by inserting two foreign genes, one from the pombe yeast, a yeast found in Africa and used to make beer, and one from the bacteria O. oeni, so that the alcoholic and malolactic fermentations, normally a two-step process, occur at the same time. While this may be a convenience to winemakers, especially those producing large quantities of wine, I am concerned for both consumers and our local economy.

The FDA’s designation of this yeast as GRAS (Generally Recognized as Safe) is questionable for a few reasons. First of all, the FDA approved the yeast based on data supplied by the developer, not based on its own study or an independent study. A developer has an interest in getting its product to market as soon as possible, whether it has been proven safe or not. Secondly, according to Professor Joseph Cummins, emeritus genetics professor at the University of Western Ontario, wine yeasts are unstable, and genetically altering them can lead to unexpected toxicity in the final product. He states that there is no evidence that the developer did any animal feeding studies to test for such toxicity and that there is no proof that the yeast and yeast DNA will not be present in the wine.

A few wineries’ decision to use this yeast could affect the entire North American market. Since these wines are unlabeled, the only way people can avoid them is to avoid all wines from North America, except those labeled organic, and few wines are labeled organic, due to the addition of sulfites during the winemaking process. Consumers in Europe and Asia are very informed regarding GMOs and have resoundingly rejected them. American consumers are becoming more aware, and polls show that a majority of Americans would prefer to avoid them.

A few wineries’ choice to use ML01 could also be a nuisance to other wineries, because this GM wine yeast could contaminate native and traditional wine yeasts through the air, surface waste and water runoff. Many wineries here in the Napa Valley are very particular about their choice of wine yeast, and contamination of these various yeast strains would truly be a shame.

I contacted many of the large producers of Napa Valley wine asking whether or not they have used this GM yeast or plan to in the future. All that responded stated emphatically that they have not used it and do not plan to. To help consumers who would prefer to avoid consuming genetically modified products make an informed wine choice and to provide an avenue for our local wineries to distinguish their wines from wines that may be using GM yeast, those that responded were listed, with their permission, on a “Shopper’s Guide to Buying Non-GMO” at on the FAQs page.

In our society, we often talk about our rights and discuss very little our responsibilities — to our neighbors, to the environment and to the community as a whole. In considering the issue of GMOs and their use, all of these factors should be taken into account.

(Martenson lives in Napa.)

Here is a current (January 2007) list of Non-GMO wine:


Wines from outside of N. America

Wines labeled “Organic”

The following wine producers we contacted stated that they do not use GM yeast:

Atlas Peak Vineyards

Beaulieu Vineyard

Buena Vista Carneros

Chappellet Winery

Charles Krug Winery

Clos Du Val Wine Company

Clos Pegase Winery

Duckhorn Vineyards

Far Niente

Flora Springs

Grgich Hills Winery

Groth Vineyards

Heitz Wine Cellars

Joseph Phelps Vineyards

Madonna Estate

Markham Winery



Robert Mondavi

Rothschild/Mondavi (Opus One)

Rubicon Estate Winery

Shafer Vineyards

Silver Oak

Spring Mountain Vineyard

Sterling Vineyards

Trefethen Vineyards

Tres Sabores

V. Sattui Winery

William Hill Estate

*If you have a local wine that you love, contact the winery, and ask if they use GM wine yeast!