WSU enologist James Harbertson and his colleagues have sampled 1,300 red wines, half of them from Washington. The research team didn’t swirl, sniff, sip and spit, but rather collected the samples with a Pasteur pipette at tastings or via donations from wineries. The samples were brought back to Harbertson’s lab and subjected to analysis with a spectrophotometer.
The result is the most comprehensive database of tannins and other phenolics in red wines to date. Tannins give red wines, strong tea, and pomegranates and other fruits their characteristic astringency and mouth feel. The database will enable winemakers to better manage their enological practices. The results of the eight-year study are published in the current issue of the American Journal of Enology and Viticulture.
While at UC Davis, Harbertson, along with Doug Adams, pioneered a relatively inexpensive method of tannin analysis, known as the Adams-Harbertson tannin assay. The assay has been commercially available for several years.
The new study establishes benchmarks for tannin levels in red wines made in Washington, Oregon, California, France and Australia. Tannins, unlike other phenols found in wine, remain relatively stable over time, making them excellent candidates for comparative analysis. Sensory scientists have established a standard, qualitative vocabulary for the description of astringency in wine; Harbertson and his colleagues think it may now be possible to connect quantitative data and other wine chemistry components to arrive at a more complete description of astringency.
Depending on the origin of the grapes in a particular wine, tannin levels varied significantly (up to 33 fold), but the mean level in each wine type (e.g., Cabernet Sauvignon, Syrah, Merlot, etc.) was about the same.
“Despite all that variation, you could still distinguish, more or less, cultivars,” Harbertson recently told Wines & Vines magazine. “I think winemakers and wine drinkers more or less understood which cultivars were more tannic by tasting, now they actually have numbers.”
The results will allow grape growers and winemakers to compare their products to a standard, although the findings don’t directly indicate the effects that viticultural or winemaking practices might have on tannin concentrations.
“The amount of tannin that gets into wine is dependent on how you deal with the fruit in the winery, so I can’t say that that difference is due to the tannin in the fruit or the way (the winemakers) make the wine,” Harbertson told Wines & Vines. “All it’s saying is wines from that place tend to be tannic. It doesn’t mean that that fruit’s tannic–it means that those wines are.”
Harbertson is based at the WSU Irrigated Agriculture Research and Extension Center in Prosser. There, with colleagues Kerry Ringer, Markus Keller and others, research is ongoing to determine what effects viticultural and enological practices have on tannins as well as terpenes, the compounds that give wines their “nose.”
Puget Sound Is Sparkling
An island of grape growing and winemaking has sprung up in Washington’s Puget Sound AVA.
Because the maritime region doesn’t get as many days of sunshine as the Sound’s sibling AVAs in eastern Washington, growers are planting varieties selected for the region by viticulturists based at the WSU Northwestern Washington Research and Extension Center in Mount Vernon.
“Five years ago there were probably only 80 acres of vineyards (in the maritime region), but it has boomed since then,” said Gary Moulton, senior scientific assistant and Mount Vernon-based viticultural researcher. “Today I estimate there are about 250 acres, mostly of small farmers with 10 acres or less.”
Popular Puget Sound varieties include Madeleine Angevine, Müller-Thurgau and Siegerrebe, as well as better known types such as Pinot Gris and Pinot Noir.
WSU’s two-pronged research and extension approach means Puget Sound winemakers are getting the information they need through workshops such as the June 30th “Winemaking Using Maritime Grapes,” led by WSU extension enologist and assistant professor of food science Kerry Ringer.
The sold-out workshop addresses one of the major concerns of Westside winemakers: what to do with grapes with high levels of acidity. Ringer has invited Domaine Ste. Michelle’s sparkling winemaker, Rick Casqueiro, to talk about the potential for sparkling wine production.
“We’re also looking at alternatives for years when the grapes just don’t get ripe because of weather,” Ringer recently told Wines & Vines. “Really, it’s just trying to give them some alternatives in their winemaking, and some ideas as to what to do with their fruit.”
Stay tuned to Voice of the Vine for upcoming workshops and other industry events as well as the latest in research news from WSU’s program in viticulture and enology.