Wine and Grape Scientists Meet near Philadelphia

ASEV-Eastern Section Conference features workshop on high pH

by By Linda Jones McKee
Left to right: Fritz Westover, Tony Wolf, Jim Kennedy and Geoff Cowey.

King of Prussia, Pa.–Although William Penn planted vinifera grape varieties from Bordeaux in 1683 in what became Philadelphia, it has taken Pennsylvania more than three centuries to develop a wine industry. In 1983 there were approximately 25 wineries in the state; now, according to WinesVines Analytics, there are 276 wineries, and the wine industry has an overall economic impact of more than $4.8 billion.

The annual conference of the American Society for Enology and Viticulture-Eastern Section met outside Philadelphia near Valley Forge National Historical Park. The 43rd conference, held July 9-11, began with a pre-conference tour of three southeastern Pennsylvania wineries: Galen Glen Winery, located in the foothills of the Pocono Mountains at an elevation of over 1,000 feet, has a cooler climate than many of the other wineries in the region; Setter Ridge Vineyards in Berks County, one of the first wineries to feel the effect of the invasive Spotted Lanternfly, lost six acres of vines last season to the pest; and Pinnacle Ridge Winery, celebrating its 25th anniversary this year, produces a range of table wines as well as sparkling wines.

Technical sessions covered a wide range of enological and grape growing topics. Andreea Botezatu, assistant professor and extension enology specialist in the department of horticultural sciences at Texas A&M University, spoke about the use of flash détente technology to improve the quality of wine made from the hybrid variety Black Spanish (a.k.a. Lenoir), which is widely grown in East Texas because of its resistance to Pierce’s disease. Another talk, given by Demetra Perry, a student of Gavin Sacks at Cornell University, looked at the use of nanofiltration-resin treatments to produce neutral wines from native American grape varieties such as Concord that normally are not used in premium red wines because of their characteristic “grapey” or “foxy” aromas.

Viticulture topics included a discussion by Hemant Gohil, extension agent at the Rutgers New Jersey Agricultural Experiment Station, about different pruning methods to revive cold-injured Merlot vines, including spur pruning (the control practice), three short canes trained onto the cordon with 5 to 10 buds, complete disbudding of the cordon, and removing the cordon by cutting the trunk 10-15 centimeters below the cordon wire while retaining one strong sucker trained onto the wire to reestablish the cordon. Other topics included a survey of leafroll associated viruses in Pennsylvania, the effect of leaf removal in the fruit zone on Cabernet Franc grown in North Carolina and Georgia, and an evaluation of under vine cover crops on Noiret vines in New York.

Taming high pH
The workshop, “Taming High pH in the East,” included presentations by two viticulturists and two enologists. The topic of high pH and how to manage it is complex, and the following summary only skims the surface of the in-depth information provided by the four scientists on the panel.

Tony Wolf, professor of viticulture at Virginia Polytechnic Institute and State University, and Fritz Westover, owner of Westover Vineyard Advising based in Houston and founder of the Virtual Viticulture Academy, addressed the topic “Potassium’s Conflicted Personality in Grapevine Nutrition.”

“High pH is a pervasive problem in many parts of the East,” Wolf said, adding the problem can come from too much potassium, despite potassium being a necessary macro-nutrient. “We need potassium; it’s important. If it’s lacking, we’ll see yield reductions.”

Excess berry accumulation is associated with elevated juice and wine pH levels. An elevated pH in a wine can negatively affect wine quality, including color stability and shelf life of that product.

Wolf suggested several ways to limit the accumulation of potassium in grape berries:
• Avoid potassium fertilizer applications to soil if the soil tests at greater than 40 ppm. 
• Exercise perfect canopy management to limit mutual leaf shading
• Choose a vineyard site with little or no 2:1 type clay soils
• Incorporate lime and target pH 6.5 to 7.0
• Use rootstocks such as 420-A that depress potassium uptake
• Try gypsum or mag-sulfate incorporation
• Consider some means of restricting root growth (e.g., shallow soil or synthetic “root bags”)
• Monitor vine potassium status visually and via plant tissue analysis to avoid potential deficiency.

Westover gave some practical advice to grape growers concerning pH. He looked at how potassium leaves the vineyard and noted that roots continually mine potassium from the soil. When it is present in soil, potassium moves slowly and can’t leech out of the soil quickly. One suggestion for growers was that if a grower samples for potassium only one time during a year, do that sample at veraison, because the nutrient sample will be more representative of the vine’s season-long nutrient status and uptake efficiency. Adjustments can then be made for the current and following seasons.

The enology aspects of high pH were presented by Geoff Cowey, senior oenologist at The Australian Wine Research Institute in Adelaide, Australia, and James Kennedy, previously director of the viticulture and enology research center at California State University, Fresno, and now president of Polyphenolics and Canandaigua Concentrate, which are both divisions of Constellation Brands.

Cowey’s talk, “Acid Matters. Getting the Balance Right,” looked at why pH is important, first in grapes, where weak acids act as buffering systems that keep a constant pH level despite small acid/base changes. The buffer capacity of each organic acid is additive, and therefore big changes are needed to adjust acidity in must or wine. Levels of pH are important also in wine, because high(er) pH favor the growth of spoilage micro-organisms such as Brettanomyces and bacteria.

In discussing ways that winemakers can try to balance their wines, Cowey noted that pH should be adjusted early, in the juice, and stated, “If the pH and TA (total acidity) balance cannot be achieved, then adjust the pH irrespective of the acid. This is more critical at this point.”

He also said that some yeasts produce more acid than others and that potassium will be extracted from the skins for approximately three days into the fermentation, so winemakers should recheck the acid level and make additional adjustments if needed. A rule of thumb is that 1 g/L of tartaric acid will reduce pH by 0.1.

Kennedy’s topic was “Optimizing Wine Color and Mouthfeel under High pH Conditions.” He pointed out that lower wine pH is associated with SO2 effectiveness, increased microbial inhibition, increased red wine color intensity and hue, and increased bentonite effectiveness. The best solution, he said, is acidification to reduce the pH level. Tartaric acid is commonly used, but a decrease in pH will also lead to an increase in the acid taste of a wine. Another solution is calcium sulfate (CaSO4) “plastering” which lowers pH without increasing total acidity (within the regulatory rules for its addition).

He commented that managing wine pH early in production is the best way to proceed and is particularly important for phenolics. Acid addition during maceration reduces the risk of tannin over-extraction, improves color extraction, and gives a head start on color stabilization. Acid added during cellaring or racking should be done primarily for fine tuning a wine.

Next year's ASEV-Eastern Section conference will be held in conjunction with the N.J. Shaulis Symposium on Vineyard Mechanization and Precision Viticulture in Geneva, N.Y., on July 16-18, 2019. The Eastern Section conference will be on July 16; the industry tour will be July 17; and the Shaulis Symposium will be on July 18.

In 2020, Eastern Section will have a joint conference with ASEV in Portland, Ore., from June 15-18, at the Marriott Portland Downtown Waterfront.


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