Growing & Winemaking


Researchers Dispute Theory About Low Yields, High Quality

December 2016
by Paul Franson

 Napa, Calif.—The universal rule about lower yields producing better wines has been pretty well debunked by scientists, but it hasn’t been accepted by all winery marketing personnel (and some winemakers) who insist lower yields equal better quality.

Further proof that this belief isn’t necessarily true was outlined in a seminar about balance at the Napa Valley Grapegrowers’ annual Rootstock conference held Nov. 8.

As vice president of viticulture, chemistry and enology at E. & J. Gallo Winery, Dr. Nick Dokoozlian is responsible for research and innovation in the areas of grape and wine production. His talk gave a rare look into Gallo’s extensive research.

Dokoozlian noted that our ideas of quality and yield come from Europe (notably, France), where he says that historically the “low yield equals high quality” equation was true due to its climate, growing practices, plant materials and viruses, but it may not apply in California.

In an attempt to sort this out, Dokoozlian developed a Grape Quality Index that correlates wine quality to price tiers and other parameters. It judges negative aromas like green pyrazines, positive aromas like red, black or jammy fruit, along with mouthfeel and correlates it all to pricing.

Dokoozlian stressed that vine leaf area exposed to the sun per gram of grapes is critical. For Cabernet Sauvignon, for example, quality rises at a steep slope to 10 to 14 cm2/g, then little improvement occurs with more leaf area.

The Gallo researcher said he is no fan of VSP trellising as a universal system, because it reduces leaf area exposed to sunlight.

Dokoozlian concluded that balanced vines accumulate higher quality at lower Brix than over- or under-cropped vines, and he theorized that an internal trigger limits sugar accumulation.

“You can achieve ripe flavors at 24º to 28º Brix with balanced vines instead of 28º Brix.” He stated, “Most Napa and Sonoma vineyards are under cropped.”

Dr. Patricia Skinkis, viticulture extension specialist and associate professor at Oregon State University, noted that Oregon winemakers have typically demanded low yields, but she believes the state could produce quality wines at higher crop levels.

The state’s 26-year average for Pinot Noir yields has been 2.2 tons per acre, but the harvests of 2014 and 2015 reached record highs at 3.2 tons per acre.

Skinkis has conducted crop load research in Oregon’s Willamette Valley for five years. Commercial growers followed careful instructions and left between 0.5 and two clusters per shoot, plus a control. Wines made with 0.5 clusters per shoot were vegetal, while the winemakers overwhelmingly selected 1.5 clusters per shoot as “optimal” in blind tests. Notably, the natural average is 1.8 clusters per shoot.

There was little difference in Brix, TA or pH in most sites with thinning. The biggest impact was on anthocyanins.

However, Oregon’s conditions are not like those of California vineyards. Growers reduce fruit to hasten ripening before rains and decrease Botrytis as well as attempt to increase quality.

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