Monday, March 21, 2011

Viticulture Research

Feature Article from the March 2011 Magazine Issue

Studying Water and Soil Effects

Studies evaluate environmental interconnectedness in winegrowing regions

by Andrew G. Reynolds
Twenty years ago winegrowing focused more on ways of manipulating grapevines, while today the emphasis is on understanding the grapevine ecosystem and the many interactions between soil, site climate, vine physiology and cultural practices. For this reason I’ve chosen terroir as a theme for this column.

Pushing the envelope in Bordeaux

Water deficits vs. the terroir effect
The impact water deficit stress has on vine shoot growth, berry weight, grape composition and overall vintage quality was investigated in several Bordeaux vineyards, and three methods for assessing water deficit stress were compared. Vine water status was assessed for three soil types during four vintages by means of stem water potential and carbon isotope discrimination measured on grape sugar. Regional water deficit was compared across 30 vintages by means of water balance modeling.

Water deficit stress anticipated shoot growth slackening, limited berry weight and enhanced berry anthocyanin content. Berry sugar content was greatest when water deficit was mild. Stem water potential measurements and carbon isotope discrimination were accurate tools for assessing vine water status on a plot scale such as this trial.

Seasonal water deficit at a regional scale can be correctly estimated by water balance models. Vintage quality in Bordeaux is determined by the intensity of water deficit stress rather than by air temperatures. The authors concluded that vine phenology and grape ripening are highly dependent on water uptake conditions. Mild water deficit stress enhances grape quality for the production of red wines. Vine water status can accurately be assessed by means of stem water potential or carbon isotope discrimination measured on grape sugars.

Quality losses through severe water stress can be avoided through the use of drought-adapted plant material, appropriate canopy management, yield reduction or the implementation of deficit irrigation.

Van Leeuwen, C.; Tregoat, O.; Chone, X.; Bois, B.; Pernet, D. ; and Gaudillere, J.-P. J. Int. Sci. Vigne Vin 43(3):121-134 (2009). Contact address of the senior author:; ENITA Bordeaux University, France.

Niagara Cabernet FrancCharacterization of wines by sensory analysisChemical and descriptive sensory analysis was conducted for nine experimental Niagara Peninsula Cabernet Franc wines from the 2005 vintage and eight wines from 2006 to illustrate differences that might support the sub-appellation system in Niagara. Twelve trained judges evaluated six aroma and flavor attributes (red fruit, black cherry, black currant, black pepper, bell pepper and green bean), and three mouthfeel sensory attributes (astringency, bitterness and acidity) plus color intensity. Data were analyzed using analysis of variance (ANOVA), principal component analysis (PCA) and discriminate analysis. ANOVA of sensory data showed regional differences for all sensory attributes.

In 2005, wines from three sites on the Escarpment Bench or Lakeshore Plain showed highest red fruit aroma and flavor. Lakeshore and Niagara River wines showed higher bell pepper and green bean aromas and flavors due to the cool growing conditions in proximity to these large bodies of water.

In 2006, all sensory attributes except black pepper aroma were different between sites. PCA revealed that wines from specific Escarpment Bench sites were higher in red fruit, black currant and black cherry aroma and flavor as well as black pepper flavor, while wines from four other sites were high in green bean and bell pepper aromas and flavors, partly due to cooler conditions within the proximity of Lake Ontario.

ANOVA of chemical data in 2005 indicated that hue, color intensity and titratable acidity were different across the sites, while in 2006, hue, color intensity and ethanol were different. These data indicated a likelihood of substantial chemical and sensory differences between clusters of sub-appellations within the Niagara Peninsula.

Rezaei, J.H., and Reynolds, A.G., Amer. J. Enol. Vitic. 61(1):1-14. Contact address of the senior author: graduate research assistant, Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, ON, Canada L2S 3A1.

Vine water status impacts wine sensory attributes The aim of this study was to examine the impact of vine water status on sensory and chemical characteristics of Cabernet Franc wines for non-irrigated sites in the Niagara Peninsula (Ontario, Canada) to assess whether vine water status might be a key factor in the determination of so-called terroir effects.

The effects of vine water status on wine sensory characteristics were studied for Cabernet Franc in the Niagara Peninsula in the 2005 and 2006 vintages. Vine water status was monitored throughout the growing season in 10 vineyard blocks using mid-day leaf water potential values. Chemical and descriptive sensory analyses were performed for nine (2005) and eight (2006) pairs of experimental wines to elucidate differences between wines from high- and low-water status (HWS, LWS) zones in each vineyard.

Twelve trained judges evaluated six aroma and six flavor attributes (red fruit, black cherry, black currant, black pepper, bell pepper and green bean) and three mouthfeel/taste (astringency, bitterness and acidity) sensory attributes, as well as color intensity. Each pair of HWS and LWS wines was compared using a t-test. Leaf water potential varied within and between vineyards in both years. In 2005, LWS wines had higher color intensity (four sites), black cherry flavor (one site), and red fruit aroma and flavor (two sites). Similar trends were observed in the 2006 vintage.

No temporal differences were found between the wines produced from the same vineyard, indicating that the attributes of these wines were consistent despite markedly different conditions during the 2005 and 2006 vintages. Partial least squares (PLS) analysis showed that leaf water potential was associated with red fruit and berry aromas, flavors and wine color intensity, as well as total phenols, Brix and anthocyanins, while soil moisture was associated with acidity, green bean and bell pepper aromas and flavors.

Measurement of mid-day leaf water potential was successful in detecting differences among vine water status levels throughout the growing seaso n. The range of leaf water potential values was almost consistent at most sites in both 2005 and 2006. Differences in vine water status resulted in wines with different composition, aroma, flavor and color intensity. At almost all sites, LWS wines were associated with high red fruit aroma and flavor, black fruit aroma and flavor, berry and wine color intensity, total phenols, anthocyanins and berry pH.

Despite two different vintages of hot and dry (2005) and wet (2006) seasons, similar trends were observed in high and low water status wines. PLS analysis illustrated that leaf water potential was positively correlated with red fruit aroma/flavor, berry color intensity, wine color intensity, total phenols and Brix, and negatively correlated with soil moisture, green bean and bell pepper aromas and flavors. The strong relationships between leaf water potential and sensory attributes of Cabernet Franc suggested that vine water status was a major basis for the terroir effect.

Rezaei, J.H., and Reynolds, A.G., J. Int. Sci. Vigne Vin 44(1):61-75 (2010). Contact address of the senior author: graduate research assistant, Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, ON, Canada L2S 3A1.

Riesling in OntarioThe roles of soil texture, vine size and vine water status 
Vine size and soil texture effects on yield components, soil, vine tissue, fruit composition and wine sensory attributes were measured in an Ontario Riesling vineyard from 1998 to 2002 to elucidate the potential basis for terroir. “Sentinel” vines were geo-located using global positioning systems. Geographic information systems (GIS) delineated spatial variation in soil texture and soil vine tissue composition (1998), and in yield components, berry composition and weight of cane prunings (vine size) for four years from each sentinel vine.

Vines were classified as “large” or “small” based on the previous season’s vine size within each of two soil texture classes (clay and sand); fruit from these four categories was separated for winemaking; berry, must and wine chemical compositional data were determined, and sensory descriptive analysis was undertaken on the wines. Correlations were observed between soil texture and composition versus berry weight and potentially volatile terpenes (PVT). There were no consistent soil texture or vine size effects on berry, must or wine composition. High vine size increased berry titratable acidity (TA) and PVT, decreased must pH and increased wine free volatile terpenes (FVT) in individual seasons. Sandy soil (versus clay soil) reduced wine TA and must PVT, and increased berry TA and must soluble solids during individual seasons.

Vine size and soil texture did not consistently affect wine sensory attributes across vintages. High vine vigor decreased mineral aroma and citrus flavor, and it increased apple attributes in individual vintages. In individual vintages, clay soil increased mineral aroma and citrus attributes but decreased apple aroma. Citrus aroma and petrol flavor increased in some vine size and soil texture combinations in one season. Vintage and wine age had greater impacts on wine sensory attributes than vine size or soil texture.

From 2005 to 2007, 10 Riesling vineyards with heterogeneous soil types were selected from throughout the Niagara Peninsula to test if soil and vine water status were important determinants of terroir, particularly monoterpene concentration and wine sensory attributes. The objectives of the project were: 1) to ascertain the impact of vine and soil water status on FVT/PVT and wine sensory attributes; 2) to enumerate the comparative magnitude of effects of soil texture, water status and vine vigor, and 3) to elucidate relationships between these variables and wine sensory quality. GIS-generated maps were analyzed by spatial correlation analysis.

In some instances, FVT/PVT were correlated with leaf water potential and/or soil moisture, suggesting that mild water stress may be beneficial for wine flavor. Sand and clay content of the soils were usually inversely correlated. Soil moisture content was usually higher in clay-dominated areas of the vineyards. Vine water status (leaf water potential) was higher in clay soils. Leaf water potential was often inversely correlated with vine size (i.e., vine water status was improved in low vine size areas). Berry weight and Brix were both positively correlated with vine water status, while TA was inversely correlated. Spatial relationships in vine water status appeared to be temporally stable, and patterns observed in 2005 appeared similar during 2006 and 2007, despite different weather conditions. In addition to these reasonably good spatial correlations between soil moisture and leaf water potential, there were strong spatial relationships between leaf water potential and both vine size and soil texture.

These observations suggest indirectly that vine size and soil texture, in addition to water status, are major contributors to the terroir effect. Wines from the 2005 and 2006 vintages were subjected to descriptive sensory analysis. Partial least squares analysis showed that the greatest percentage of sensory attributes were associated with leaf water potential, soil moisture and vine size.

Reynolds, A.G.; de Savigny, C.; and Willwerth, J.J., Progres Agricolet Viticole 127(10):212-222. Contact address of the senior author: Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, ON, Canada L2S 3A1.

Terroir factorsHow growing conditions impact Riesling wine sensory profilesThe major focus of this research was to explain terroir effects that might impact wine varietal character. Authors sought to elucidate potential determinants of terroir by choosing vine water status as a major factor of the terroir effect.

One hypothesis was that consistent water status zones could be identified within vineyard sites and that differences in wine sensory attributes could be related to vine water status. To test this hypothesis, 10 commercial Riesling vineyards representative of each sub-appellation created by the Vintners Quality Alliance of Ontario were selected within the Niagara Peninsula. These vineyards were delineated using global positioning systems (GPS), and 75 to 80 sentinel vines were geo-referenced within a sampling grid for data collection.

During the 2005-07 growing seasons, vine water status measurements (mid-day leaf water potential) were collected bi-weekly from a subset of these sentinel vines. Data were collected on soil texture and composition, soil moisture, vine performance (yield components; vine size) and fruit composition. These variables were mapped using GIS software, and relationships between them were elucidated. Vines were categorized into “low” and “high” water status regions within each vineyard block through the use of these geospatial maps and replicate wines were made from each region.

Many geospatial patterns and relationships were found to be spatially and temporarily stable within vineyards. Vine water status was found to be temporally stable within vineyards despite different weather conditions during each growing season. Generally, spatial relationships between vine water status, soil moisture, vine size, berry weight and yield also were stable from year to year. Vine water status also had some impact on the fruit composition in several vineyards.

A sorting task (multidimensional scaling) was performed on wines from the 2005 and 2006 vintages, and wines of similar water status had similar sensory properties. Descriptive analysis using a trained panel further indicated that water status had an effect on wine sensory profiles. Similar attributes were different for wines from different water status zones. Through multivariate analyses, specific sensory attributes, viticulture and chemical variables were associated with wines of different water status. Vine water status was a major contributor to the terroir effect, as it had a major impact on vine size, berry weight and wine sensory characteristics.

Willwerth, J.J.; Reynolds, A.G.; and Lesschaeve, I., Progres Agricolet Viticole 127(8):159-168 (2010). Contact address of the senior author: Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, ON, Canada L2S 3A1.

Andrew G. Reynolds is professor of biological sciences/viticulture at the Cool Climate Oenology and Viticulture Institute at Brock University in St. Catharines, Ontario. He has written the Wine East column “What’s New in Research: Summaries of Current Literature on Grapes and Wine” for Wine East since 1997.

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