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Sensory Science, Microclimates

Posted by | July 24, 2008

Pucker Up for Sensory Science

Volunteers tasted red wines in a study designed to correlate astrigency with tannin levels in red wine.

Volunteers tasted red wines in a study designed to correlate astrigency with tannin levels in red wine.

Astringency or “mouth feel” in wine has long been attributed to the presence of tannins and other phenolic compounds. Because astringency is an at least somewhat subjective evaluation, though, scientists at WSU tested the assumption that the level of tannins present in red wines made in Washington correlates with perceived astringency.

In a paper published in a recent issue of the American Journal of Enology and Viticulture, lead author Josie Landon, a graduate student who worked with sensory food scientist Carolyn Ross, set up two tasting panels. One panel was composed of untrained tasters, the other of trained tasters. Both panels tasted three different wines that had been categorized according to the level of tannins and other taste and color compounds present in each.

Tannin levels were measured using the Adams-Harbertson assay; the assay was the key tool used in a groundbreaking survey of 1,300 red wines conducted by WSU researchers, as described in a previous issue of Voice of the Vine (http://tinyurl.com/55oyta).

All the tasters in the study were able to distinguish differences in perceived astringency in Washington reds, and these results correlated strongly with the tannin concentrations in the individual wines.

Although similar studies have been conducted in the past, they’ve been conducted using “model wine solutions,” according to Landon et al.’s paper. The WSU study used real wine.

The Landon et al. study is a facet in a larger effort by WSU researchers to quantify what until now has been subjective and anecdotal, namely, the viticultural and enological practices that result in consumers perceiving a wine as being of premium quality.

For more on tannin research at WSU, please visit: http://bit.ly/hJAsvg.

It’s a Microclimate Thing

Using specially designed heater-cooler technology, along with vine training, allowed Tarara (escaping the heat of the vineyard in the bottom picture) and her colleagues to subject individual vines to four different microclimates.

Using specially designed heater-cooler technology, along with vine training, allowed Tarara (escaping the heat of the vineyard in the bottom picture) and her colleagues to subject individual vines to four different microclimates.

Premium wines depend upon premium grapes, which is why horticultural scientist Julie Tarara conducted a series of experiments to test the effects of sun, shade and heat on Merlot grape quality.

Tarara, a USDA Agricultural Research Services scientist based at WSU’s Irrigated Agriculture Research and Extension Center in Prosser, along with Sara Spayd, conducted experiments that, through clever design, isolated the contributions of sun, shade and temperature to berry development so that their effects could be independently measured in ripe fruit.

“Unlike us,” Tarara said, “plants can’t sit in the shade or put on another sweater. It’s important to understand how the environment affects grapevine biology.”

By controlling for the effects of light and temperature in an actual vineyard (as opposed to a greenhouse, a much more controlled and therefore less “real world” environment), Tarara learned that fruit acidity was inversely affected by temperature: “the greater the heat, the lower the acidity,” she and Spayd wrote in an article for Good Fruit Grower. Acidity in fruit, including grapes, provides a welcome sensation of freshness, but also reduces the cloying sensation of too much sugar.

High temperatures, Tarara found, resulted in lower concentrations of anthocyanins, the compound that gives red grapes their color. But lots of sun resulted in high concentrations of the desirable anthocyanins as well as flavanols, the group of compounds found in grapes, cocoa and green tea that are thought to improve cardiovascular health and to scavenge for the toxic free radicals responsible for oxidation damage to DNA and low-density lipoproteins (the “bad” cholesterol).

Keeping grapevines cool, Tarara notes, can be accomplished by manipulating the canopy so that fruit is partially shaded. It’s a delicate balancing act, though, requiring close attention being paid to the vineyard’s microclimates.

To learn more about Tarara’s viticultural research, please visit: http://bit.ly/hJNhS8