Stag’s Leap Wine Cellars

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Stag’s Leap Wine Cellars

Winemaking Articles

Front row (left to right): Lab Technicians Lupe Ochoa, Betty Roldan and Angel Cervantes. Back row (left to right): Assistant Winemaker Jim Duane and Enologist Mark Lucci

The pHunction of Science in Winemaking

The definition of enology is the scientific study and making of wine; however, in most California wineries, an enologist is not synonymous with a winemaker. Winemaking duties can range from overseeing vineyards to cellar operations to blending and bottling. An enologist is always focused on the wine itself, analyzing and evaluating it at every stage of development to ensure its soundness and quality before leaving the winery. “Our job is often described as keeping the wine healthy,” says Stag’s Leap Wine Cellars Enologist Mark Lucci. “In another industry, we might be considered the quality control department.”

At Stag’s Leap Wine Cellars the enologist’s job starts before the grapes arrive at the winery and lasts until the final drop goes into the bottle. Early in the season the enologist and lab technicians generate baseline numbers on each vineyard block, measuring cluster and berry weight, sugar, acid, and pH levels of the grapes. These measurements give the winemakers objective data that help determine when the grapes will be ready for harvest. Along with qualitative data such as how the grapes taste, this objective analysis is crucial in determining the right time to harvest.

One of the busiest times is during harvest. After the grapes arrive from the vineyard, the enology team focuses on fermentation - yeast converting grape sugar to alcohol. The juice is analyzed to make sure the yeast has the nutrients it needs to perform the conversion. To track the daily progress of the fermentation, the team uses a hand held electronic density meter which measures the decreasing sugar level, letting them know when fermentation is finalized.

“With multiple fermentations occurring simultaneously,” says Mark, “the density meter is a critical tool for gathering daily measurements to make sure the fermentations are consistently progressing in line with the strict standards of Winemaker Nicki Pruss.” After fermentations are complete the wine is moved to either tanks or barrels to age. The aging wine is tested monthly which means at any given time the lab is analyzing dozens of wines across multiple vintages. The analyses performed help verify there are no unwanted microscopic organisms that can cause wine spoilage. The lab also measures for sulfites, which can protect wine from microbial growth and the damaging effects of oxygen. Additionally, they monitor for optimal levels of temperature and humidity, allowing the wine to age properly.

Subsequent to aging in barrels, the blended wines are ready to be bottled. Using enological instruments to measure pH, acidity, and alcohol, the lab analyzes the wine one last time to verify it has the physical composition intended by the winemaker. As a final step from vineyard to bottle, Mark works with Bottling Supervisor Jan Phillips to confirm that the bottles are filling to the correct height, and that the oxygen levels in the bottles are low, which gives the wines their aging ability. Throughout the year and until a wine is bottled, the enologist and lab technicians provide invaluable scientific data to the viticulture and winemaking teams. These quantitative reports help to ensure the Stag’s Leap Wine Cellars wine you are enjoying today blends the best of both worlds – art and science.