Uncork a bottle of fine California wine and the delightful aroma it exudes is called bouquet.
But multiply that bottle by the millions produced in the Central Valley, and regulators refer to those same wine gases by a less pleasant name: smog-forming pollution.
By the standard the U.S. Environmental Protection Agency uses to gauge the severity of smog, the San Joaquin Valley in recent years has surpassed Los Angeles and Houston to become America's bad air capital.
Charged with cleaning up the country's dirtiest air, the San Joaquin Valley Air Pollution Control District is preparing to adopt the nation's first air quality restrictions on winemaking.
The gases wafting from the valley's sprawling wineries, which produce most of the wine made in America, do not rank with car exhaust or cow flatulence as leading causes of the region's thickening air pollution. But regulators maintain that the wineries are giving off far more than a subtle hint of unhealthful air.
The San Joaquin Valley's 109 wineries emit 788 tons a year of smog-forming gases, air pollution officials estimate. The vintners -- which include E.&J. Gallo, Ironstone and Bronco -- are some of the world's biggest winemakers, producing more than 300 million gallons of wine annually. The largest valley wineries mass-produce a wide array of red, white and blush wines, but their biggest volume is in inexpensive table wines sold in bulk sizes.
The district is scheduled to approve the proposed regulations before the end of the year. As it stands, the rules would require mass producers of wine to install on their fermentation tanks the pollution controls that are typically used in oil refineries and steel mills.
The equipment, which could cost each large winery millions of dollars, would be used primarily to catch wayward emissions of ethanol, alcohol produced during the fermentation of wine. Ethanol is considered a volatile organic compound, one of two major classes of pollutants that combine to create smog.
Winemakers say that they are willing to help clean the valley's air but are concerned that ill-conceived pollution controls could collect bacteria and contaminate their carefully crafted Pinot Grigios, Merlots and Chardonnays.
"The industry in general is for clean air. We are environmentally conscious, we have a code of sustainable wine growing practices," said Chris Indelicato, chief executive of Delicato Vineyards and scion of one of California's oldest wine families.
"The problem here is that this is going to cost millions of dollars, and it's not even proven to work," he said. "And there would not even be that much of a benefit, because we really are not gross polluters."
Industry lawyers and winemaking engineers say that by sucking wine vapors from the fermentation tanks like vacuums, the pollution controls could even harm the smell and taste of wines, one of California's most celebrated exports.
"It's technology that is used on refineries. But you don't drink gasoline," said Wendell Lee, an attorney for the Wine Institute, a trade association representing more than 800 California wineries. "We want to help improve air quality, but not in a way that compromises the winemaking tradition."
Acknowledging that the pollution controls have the potential to affect food sanitation and the flavor of wines, San Joaquin air officials said last week that they are considering revisions to their proposed rule that would allow wineries to effectively buy their way out of the requirements.
In exchange for not installing the equipment on fermentation tanks, large wineries would have to make similar pollution reductions elsewhere in the San Joaquin Valley, such as reducing emissions from their delivery truck fleets or paying to curtail air pollution from other businesses, said Seyed Sadredin, the district's deputy air pollution control officer.
"The old days when we just copied the rules" of Los Angeles-area smog regulators "are long gone," Sadredin said. "We are leading the world in developing solutions to our own problems, which in many ways are now worse than the problems in Southern California."
Though the region is rapidly becoming urbanized, much of its pollution comes from its large agribusiness operations. As a result, air quality officials have begun proposing a series of groundbreaking rules to slash air pollution from previously unregulated sources, such as dairy cows, and are offering incentives to replace old diesel-burning water pumps and farm tractors with cleaner, more modern equipment.
Households are also being required to cut back the pollution they emit with a rule that prohibits the burning of logs in fireplaces on days when smog reaches unhealthful levels.