Scientia Vitis: Decanting the Chemistry of Wine Flavor

Pasteur studying the diseases of wine in 1863.

Pasteur studying the diseases of wine in 1863.

State of the Art

The Hilgard Project is introducing contemporary quantitative measures to other aspects of wine production as well. Boulton installed pressure transducer sensors in three large, metallic vats in the UC Davis teaching winery to demonstrate that the devices can replace the standard rudimentary observations used during large-scale winemaking. “They allow us to monitor the sugar consumption that occurs during the fermentation process and to diagnose problems,” he explains. The device is intended to replace more traditional hydrometers—floating devices used to monitor the density of fermenting juices. Because liquid exerts a buoyancy force equal to the weight of the displaced volume, the device floats higher in dense fluid. Juice is usually denser before fermentation, when there are more dissolved solids. As the fermentation process completes, the dissolved sugars are burned up, and the hydrometer begins to sink.

“We get more accurate readings with sensors,” says Boulton. Because pressure transducer sensors are installed at the bottom of the vat, they deliver an overall average reading of the juice weight. The readings from hydrometers, however, are more local and therefore often cause sampling errors—especially when the juices are not well mixed. Boulton admits that on a vat-by-vat basis, the detailed measurements probably don’t lead to production of a higher quality wine—the end product isn’t likely to be any better than would come from a process that uses a hydrometer. “The idea is to collect data that can be used to understand wide-scale patterns in fermentation chemistry,” he says.

The data collection process supported by the Hilgard Project is part of a long trend toward automation and computation. Biosensors are being developed in research labs to help measure esters and alcohols at the molecular level, and remote sensing data are used to study the impacts of climate change on vineyards.

For all of the efforts toward systematic measurement methods, however, the structure of wine flavor hasn’t become any more lucid. New molecules are discovered in wine every year, but very few are shown to play a direct role in flavor or aroma. “Fifty years ago people believed there was a molecule that made Riesling or Pinot Noir unique, but now we realize it’s infinitely more complicated,” says Heymann. Even as future research correlates core aspects of wine back to flavor molecules, the synergistic interactions between key compounds will have to be analyzed.

In the meantime, Boulton and Heymann encourage people to take science into their own hands—perhaps by turning the living room or kitchen table into a wine tasting laboratory, and implementing some of Heymann’s taste-testing methods at home. “We recommend people form groups, taste wines, and look for descriptors,” says Boulton. “Start with your favorite fruit wines and cups of different fruit jellies. Anything that gets people thinking about wine from an analytic perspective helps the field move forward.”

Amy Coombs is a science writer and editor who lives in the San Francisco Bay Area.