The Essential Book of Fermentation (25 page)

At first, the National Organic Standards Board, the group charged with defining organic for the USDA, proposed that sulfites be allowed in organic wine. The USDA changed that, disallowing their use in any wine labeled organic, and furthermore disallowing any use of the word “organic” on wine labels if sulfites were added, even if the grapes were organically grown. The wine industry in general, led by the organic segment, reacted vehemently against that rule. It believed that the USDA was trying to marginalize the whole sphere of organic wines by limiting the name to those few producers—and there are just a handful—who use organic grapes and refuse to sulfite their wines. The Organic Grapes into Wine Alliance, Bonterra Vineyards, the Organic Wine Company and Chartrand Imports (importers of organic wines from Europe), Fitzpatrick Winery, Badger Mountain Vineyard, and many other organizations fought the USDA on this and won, partially.

As the final rule now stands, only wines made from organically certified grapes and made without added sulfites can be labeled as “organic wine.” Wines made from organically grown grapes with the addition of 100 ppm sulfites or less can state “made from organically grown grapes” on the label. That seems fair enough. But there may be more wrinkles. Brian Fitzpatrick of Fitzpatrick Winery in Somerset, California, told me that “the interpretation of the labeling is still not clear. For instance, there will be a 100 Percent Organic label—certified grapes and no sulfites—and there will be a USDA Organic seal on the bottle. Then there is a different USDA Organic seal that ensures that at least 95 percent of the product is made from organic ingredients.” There will be a USDA seal on that bottle, too. Then, he said, there is a label where only 70 percent of the product must be from organic sources: the words “Made from Organically Grown Grapes” may be allowed on the label, but the USDA Organic seal may not be used. The problem, according to Fitzpatrick, is that wine made entirely from organic grapes with sulfites added (by far the largest amount of wine falls into this category) may be treated under the 70 percent rule and not gain the USDA seal, even though it meets the criteria for the 95 percent rule. “Does that help?” Fitzpatrick asked. Well, it sounds as if the definition of what’s organic has fallen into the hands of USDA bureaucrats, with predictable results. I suggest you simply read the label closely. It will tell you the status of the grapes used to make the wine. It may even say “Vegan Wine.” That’s wine made with no animal-derived fining agent, such as egg whites or isinglass (the latter derived from fish). Fining agents carry a slight electrical charge on their surfaces that draws cloudy particles and impurities to them. These clump together and precipitate out of the wine, leaving it clear. Some winemakers believe that fining removes some of the nuance of the wine and don’t do it. Most use fining agents. If vegan wine is fined at all, it is with bentonite clay, a natural mineral product.

Yeast and Wine

Wine was originally made by spontaneous fermentation; that is, whatever yeast and bacteria happened to colonize the grape skins or came floating along and landed in the grape juice fermented that juice into wine. But in modern times, vintners have begun using pure strains of specific types of yeast. This enables them to better predict what the finished wine will be like and how the fermentation will proceed, but it also means the loss of the complex flavors created by a diversity of microorganisms. “Now we’re looking at using natural mixes of organisms again not only for their ability to add complex flavors to wine, but because a healthy mix of microorganisms reduces the chance of spoilage,” says Tom Tiburzi, winemaker at Domaine Chandon in Yountville, California. “In Switzerland in the 1970s, cheesemakers started using pure strains of starter bacteria and they suddenly found the holes in the cheese were gone. People wanted the holes. So they needed to go find the wild microorganisms that made the holes in the cheese and reintroduce them into the process.”

While
Saccharomyces cerevisiae
and
S. bayanus
are the primary fermentation yeasts, many others can come into the vats on the skins.
Kloeckera,
Metschnikowia,
Kluyveromyces, Candida,
and
Pichia
are all common genera of yeasts that may take part in fermentation, but they tend to die off as the
Saccharomyces
species gets going and starts building up alcohol levels. Alcohol, being a by-product of yeast metabolism, is toxic to yeast when it reaches certain levels. Some yeast die off when alcohol reaches just 6 or 7 percent; others can withstand a few percentage points more.
S. cerevisiae
and
S. bayanus,
however, can withstand alcohol levels up to 17 percent or so before dying off, and that’s why they are used as pure strains.

Tiburzi told me a story that points up the problems with trying to manipulate yeast instead of letting nature take its course in the production of wine. Yeast produces hydrogen sulfide as a precursor to amino acids in wine. Now, hydrogen sulfide is a gas that smells like rotten eggs—not something you want in the nose of your Merlot. During rapid fermentation, the hydrogen sulfide disintegrates as the sulfur in its molecule is used to build amino acids—which are good things in wine. However, toward the end of the fermentation, when the yeast are weak from having used up most of the nitrogen in the must (must is a winemaker’s term of art and refers to the fermenting crushed grape and juice), they leave much of the hydrogen sulfide unchanged instead of transferring it into amino acids, which leaves the wine smelling awful. So scientists have taken to adding yeast nutrient (nitrogen) to fermenting musts in the form of diammonium phosphate (DAP) so that the yeast will stay vital long enough to clean up the hydrogen sulfide.

So far so good. But in a related matter, yeast also excretes urea during rapid fermentation. Urea in a hot wine tank can be transformed into ethyl carbamate. Ethyl carbamate is a close relative of carbaryl—which is a pesticide known as Sevin. Because ethyl carbamate is a suspected human carcinogen, several countries have imposed restrictions on the amount permitted in wine. The saving grace is that yeast will use up the urea at the end of the fermentation, taking its molecule apart to get at its nitrogen (remember, nitrogen is a yeast nutrient). Therefore, it’s no longer available to be transformed into ethyl carbamate. Except, and here’s the kicker,
except
when diammonium phosphate is present. Then they’ll go for the nitrogen in the DAP and the unused urea can be transformed into the carcinogen. The simple solution would be to make wine naturally and not add diammonium phosphate to it. But here come the genetic engineers again. According to Linda Bisson, a professor in the Department of Viticulture and Enology at UC Davis, they are trying to “make wine safer for human consumption. . . . An example is our efforts to genetically engineer strains [of
Saccharomyces cerevisiae
] that reduce the appearance of ethyl carbamate in the fermentation environment.”

That’s noble, but it reminds me of the situation with nitrogen-fixing soil bacteria, whereby these little farmer’s helpers will take nitrogen from the air and turn it into fertilizer for crops—
except
when the soil is flooded with chemical nitrogen. Then they lose their ability to fix nitrogen. Thus the farmer pays good money for an expensive fertilizer that turns off a natural mechanism that was giving the same fertilizer to him for free. Similarly, there are natural, nonchemical ways to control weeds in crops. Herbicides are used, but they can damage the crops as well as the weeds. Instead of simply using natural weed controls, scientists are genetically engineering crops to withstand the chemical assault of herbicides.

Saccharomyces
is added as a pure strain to grape juice the way we add it to flour and water to make bread dough—and just being in a winery will seed the grape juice with enormous numbers of these yeast cells. “Grape juice is a wonderfully selective medium for
Saccharomyces
,” says David Mills, assistant professor of microbial ecology and bacterial genetics at UC Davis. “The winery has billions and billions of
Saccharomyces
cells all over the place from previous fermentations. Therefore, carrying juice through the winery without it getting inoculated with resident
Saccharomyces
is problematic. I tell my students that it would be like trying to walk through a car wash without getting wet.”

A yeast named
Brettanomyces intermedius
is a problem in wineries, because, although it takes part in alcoholic fermentation, it yields haziness, high concentrations of acetic acid (a vinegary taint known as volatile acidity), and a particularly unpleasant smell called “mousiness.” Brett, as it is called, is definitely a spoilage organism, but cleanliness in the winery and the use of 100 ppm sulfites in the wine usually control the problem.

Winemakers today are increasingly allowing fermentations to proceed with the yeasts that occur naturally on the grape skins. They feel that each of the many yeast species adds its certain “something” to the flavor complexity of the wine. While most of these natural yeasts die off at lower alcohol levels, winemakers keep the fermentations going to dryness, if that’s their goal, by adding commercial wine yeasts that blow through the remaining sugar quickly and completely as the natural yeasts die off.

Fiddling with Yeast Genes

What if the grapes are grown organically and no sulfites are used but the juice is fermented by yeast that has been genetically modified? Could it be labeled organic wine? Technically, no. But in the United States, the wine could still be labeled organic because there is no way to know whether a GMO (genetically modified organism, yeast in this case) has gotten into the fermenting must. The government does not require that products containing GMOs be labeled as such. That’s not true in other countries, especially Europe and South Africa, where there’s a large wine industry and a growing distaste for anything with GMOs in it.

In Australia and the United States, much research is being done on modifying wine yeast (our old friend
Saccharomyces cerevisiae
) genetically, and consumer fears about the potential dangers are generally dismissed by researchers. Professor Linda Bisson recently wrote, “Consumers raise another issue, that the process of genetic exchange and mutation is unnatural and therefore undesired. This view is of course not correct . . . The risks to human health and well-being of the generation of such modified strains of
Saccharomyces
for food and beverage production are minimal.”

Is it too far-fetched to suppose that a genetically modified strain of
Saccharomyces
could be engineered against which the human immune system has no defense? Professor Bisson’s blanket statement, “This view is of course not correct,” sounds like the kind of hubris that the fates love to humble.

Scientists know that yeast fermentation of grape juice creates esters that give those wonderful fruity aromas and flavors to wine, such as apple, banana, fruity-flowery, and tropical fruit aromas. The yeast performs these miracles by manufacturing enzymes that work on grape juice to produce acetate esters. In one study, scientists investigated the feasibility of improving the aromas of Chenin Blanc by overexpressing the gene within the genetic structure of
S. cerevisiae
that makes an enzyme that creates a fruity ester. Usually this enzyme’s manufacture by the yeast cell is controlled naturally by an on-off switch in one of the yeast’s genes, with the switch setting determined by environmental conditions. If conditions are right, the yeast makes the enzyme; if conditions aren’t right, nature in her wisdom shuts off the gene. Along come the genetic engineers, who say, “Let’s throw the switch on permanently and see what happens.” Sort of like the Sorcerer’s Apprentice and the brooms and buckets. They tried it—and what happened? Here is the study’s conclusion: “Overexpression of acetyltransferase genes may affect the flavor profiles of wines deficient in aroma, thereby allowing for the production of products maintaining a fruitier character for longer periods after bottling.” In other words, it works.

In another example from the study: “Researchers at the Australian Wine Research Institute are using genetically engineered yeasts to increase the flavor of wines. Australian viticulturists like their grapes to fully ripen so they impart more flavor to the wine, but ripe grapes contain more sugar, which, when fermented, leads to wines containing higher alcohol concentrations. High alcohol wines tend to exhibit a ‘hot’ flavor, which winemakers, and more important, consumers, don’t like. AWRI has genetically modified yeast to produce more glycerol and less sucrose. This will reduce the alcohol levels.” In other words, this GMO turns some of the carbon, hydrogen, and oxygen atoms in the grape juice to glycerol rather than to grape sugar. Yeast turns sugar to alcohol, but not glycerol, hence final alcohol levels are suppressed.