THE WALLA WALLA VALLEY AVA, PAG. 1 EFFECTS OF VINEYARD SOIL PROPERTIES ON THE PHENOLIC COMPOSITION OF SYRAH GRAPES FROM THE WALLA WALLA VALLEY AVA Snejana KARAKIS 1, Barry CAMERON, Kevin POGUE 1 Department of Geosciences, University of Wisconsin-Milwaukee, PO Box 413, Milwaukee, WI 53201 USA 22902 *Corresponding author: Karakis. E-mail: karakis@uwm.edu Introduction The concept of terroir has been evaluated since the 12 th century, when the Cistercian monks of Burgundy realized that the physical environment in which grapes are grown has a major influence on the character and quality of grapes and resulting wine. The unique characteristics of a vineyard, including factors such as the geology, soil, landscape, and climate contribute collectively to the quality of the grapes and sensory attributes of the wine produced in that vineyard (Wilson, 1998; Haynes, 1999; White et al., 2009). Grape phenolic compounds, which are secondary metabolites that develop in the skin and seeds of grapes during ripening are associated with grape and wine quality. Phenolics are also known to provide various human health benefits due to their antioxidant and anti-inflammatory properties (Cortell and Kennedy, 2006; Koundouras et al., 2006; Di Majo et al., 2008; Kennedy, 2008; Teixeira et al., 2013; Anesi et al., 2015). The phenolic synthesis and accumulation in grapes and therefore grape berry phenolic content are influenced by terroir factors, including the cultivated variety and the physical environment conditions affecting the vine nutritional and water status (Bergqvist et al., 2001; Cortell and Kennedy, 2006; Gómez-Míguez et al., 2006; Koundouras et al., 2006; Cohen and Kennedy, 2010; Ubalde et al., 2010; Van Leeuwen, 2010; Teixeira et al., 2013). In particular, the vineyard soil is a key terroir element, contributing a substantial control on the grapevine nutritional and water status, as demonstrated by the grape quality variability at the vineyard level resulting from soil heterogeneity (Bramley et al., 2011). The transformations that occur in the seed and skin phenolics during grape berry maturation have a fundamental influence on wine quality because the phenolic content of grapes ultimately influences the balance, taste, color, consistency, and aroma of wines. Although wine phenolic compounds can also be the product of microbial activity and oak sources, most phenolic compounds found in wine are derived from grapes and depend on factors such as grape variety, vineyard physical environment, vineyard management, and vinification techniques (Kennedy, 2008). Koundouras et al. (2006) compared the phenolic composition of grape berries and associated wines produced using the same vinification techniques over two vintages, and found that grapes with high concentrations of phenolic compounds produce wines with high phenolic content. As wine quality is driven by the phenolic content of grapes, the concentrations of phenolics that can be extracted into wines are dependent on the concentrations of phenolics available in the grapes (Cortell et al., 2005); and maximizing the grape phenolic content promotes enhanced organoleptic properties and overall quality of wines. Thus, understanding the controls on phenolic synthesis and accumulation in grapes, which include the vineyard soil as a basic terroir factor influencing the vine nutritional and water status, is critical for harvest and wine making decisions.
THE WALLA WALLA VALLEY AVA, PAG. 2 MATERIALS AND METHODS Study Area The study area encompasses approximately 48,000 acres in the southeast quadrant of the Walla Walla Valley American Viticultural Area (AVA), and includes 11 vineyards planted with syrah grapes across different terroirs (Fig. 1). The tumultuous geological history of the Walla Walla Valley consists of massive eruptions of the Columbia River Basalt lavas during the Miocene (17-15 Ma); vast recurring Pleistocene glacial outburst flooding events (Missoula floods) between 15,300 and 12,700 years ago, forming graded rhythmites (Touchet beds); and deposition of wind-blown loess of various thicknesses (Meinert and Bussaca, 2000; Pogue, 2009). Four different and very distinctive terroirs are found across the study area in the Walla Walla Valley AVA. Terroir 1 is largely encountered below elevations of 366 meters (1,200 feet), consists of loess layers of fine wind-blown silt deposits extending two to four feet deep over Missoula flood sediments, and is represented by Pepperbridge, Seven Hills, and Va Piano vineyards. Terroir 2 is generally found above elevations of 366 meters (1,200 feet), consists of thick loess deposits that can be eight to ten feet thick overlying basalt bedrock, and is characterized by Les Collines, Leonetti Loess, and Dwelley vineyards. Terroir 3 is typically located on steep slopes in foothills and canyons, consists of very thin loess layers of very fine, wind-blown silt extending only a few inches over weathered basalt bedrock that underlies the entire region, and is represented by Ferguson and South Wind vineyards. Terroir 4 is predominantly found at the lowest elevations on the Walla Walla River and Mill Creek floodplains, consists of cobblestone river gravels of an ancient riverbed, and is characterized by Cayuse, SJR, and Old Stones vineyards. Figure 1: Study area located in the southeast quadrant of the Walla Walla Valley AVA.
THE WALLA WALLA VALLEY AVA, PAG. 3 Soil Assessment To minimize microscale variation flattening, collocated soil and grape samples were collected from each study vineyard in September 2014. Soil profiles were advanced and sampled throughout the vineyards in the study area to maximum depths of 50 centimeters below ground surface. The soil texture was determined through grain size analysis via a Malvern Mastersizer 2000E laser diffraction particle-size analyzer. Total major and select minor and trace element compositions were determined on the fine fraction of the vineyard soil samples, which were powdered and fused for x- ray fluorescence (XRF) analysis. Loss on ignition (LOI) was determined by heating 1 gram of sample for 10 minutes in a muffle furnace at 1050 C and calculating the mass difference. The major element and select minor and trace element compositions were obtained from glass disks fused at 1050 C in a Claisse M4 fluxer and analyzed using a Bruker S4 Pioneer XRF in the Department of Geosciences, at University of Wisconsin Milwaukee. Grape Phenolic Panel Grape samples were collected from each study vineyard during the September 2014 harvest. Two to three grape clusters were collected from each vineyard, and approximately 250 grams of loose berries were weighed, placed in sealable plastic bags, and frozen prior to being submitted for analysis. Grape phenolic profile analyses were performed by ETS Laboratory in Saint Helena, California by high performance liquid chromatography. The grape phenolic profile analysis includes Brix measurements and concentrations of catechins, quercetin glycosides, tannins, total anthocyanins, and polymeric anthocyanins. Data and Maps Vineyard-specific data collected during the 2014 harvest, as well as data from the Web Soil Survey (WSS, http://websoilsurvey.nrcs.usda.gov/) managed by the USDA NRCS were utilized in this study. Data were plotted using the geographic information system software program Esri ArcGIS Desktop to geospatially characterize the study area vineyards. WSS soil properties were assessed utilizing the USDA NRCS Soil Data Viewer tool built as an extension to ArcMap, which facilitates spatial mapping of soil properties from the WSS attribute database. Results and discussion Vineyard Soil Properties The vineyard soils across the study area developed on top of various types of parent materials, ranging from loess, silty loess over calcareous lacustrine, and glacio-fluvial deposits (Terroir 1), loess deposits (Terroir 2), loess mixed with colluvium from basalt deposits (Terroir 3) and mixed, very gravelly alluvium deposits (Terroir 4). The vineyard soils, which consist of silt loam in Terroirs 1 and 2, very stony loam in Terroir 3, and very cobbly loam in Terroir 4, contribute different textures and depths, affecting the available nutrients and water holding capacity of the soil. Soil drainage, ranging from well drained soils across Terroirs 1, 2, and 3 to somewhat excessively drained soils in Terroir 4, indicates overall good draining conditions for the vines across the study area. The available water holding capacity (AWC) and organic matter (OM) values, which are lowest in the vineyard soils from Terroirs 3 and 4 indicate optimal viticultural conditions in these areas (Fig. 2).
KARAKIS ET AL., EFFECTS OF VINEYARD SOIL PROPERTIES ON THE PHENOLIC COMPOSITION OF SYRAH GRAPES FROM THE WALLA WALLA VALLEY AVA, PAG. 4 Figure 2: Spatial mapping of soil properties obtained from the USDA WSS attribute database. Based on the grain size analysis, silt sized grains dominate the textures of the soil samples collected throughout the vineyards, with an average silt content of 76.6%, average sand content of 15.8%, and average clay content of 7.55%. The soils plot in the silt loam and silt fields of the USDA soil texture triangle (Fig. 3), and these textures are in general agreement with the USDA taxonomic classification for these soils. Figure 3: Vineyard Soils Plotted on the USDA Soil Texture Triangle. The red symbols represent the soils of Terroirs 1, 3, and 4, which are silt loam, whereas the blue symbols represent the soils of Terroir 2, which are silt. Soil depths range from 46 to 165 cm, indicating that best vine conditions are represent by shallowest soil vineyards located in Terroir 3. Among the four terroirs, the vineyard soil samples containing the highest average clay content (8.75%) were collected from Terroir 3, which corresponds to the shallowest soil depths and highest
THE WALLA WALLA VALLEY AVA, PAG. 5 average elevations. The vineyard soil samples containing the highest average sand content (21.85%) were collected from Terroir 4. The XRF total elemental analysis conducted on the fine fraction (silt and clay) of the soil samples indicates some variation in the chemical composition of the vineyard soils. These elemental abundances represent the total concentrations in the soil and are indicative of the general vineyard soil composition in terms of chemical evolution over the developmental history of the soils. Overall, the most variability in total concentrations is noted for the following oxides: SiO 2 (55.4 65.7%), Fe 2O 3 (5.5 10.2%), and CaO (2.3 5.3%). The compositional variation of the soils is illustrated spatially on maps depicting interpolated concentrations across the study area using Esri ArcGIS ordinary kriging (Fig. 4). Figure 4: Spatial mapping of vineyard soil chemical composition. Overall, the soils with the highest SiO 2 and Al 2O 3 and lowest TiO 2, Fe 2O 3, CaO, and MgO compositions correspond to the vineyards of Terroir 2, consisting of thick loess over basalt. The soils with the lowest SiO 2 and highest TiO 2 and Fe 2O 3 content are present near the southwest part of the study area in Terroir 4 consisting of basalt cobblestone gravels. The soils with the highest CaO and MgO compositions also coincide with Terroir 4, and extend further into the lower half of the study area into Terroir 3 consisting of thin loess over weathered basalt. The vineyard soils of Terroir 3 also coincide with the lowest Al 2O 3 content among the four terroirs. The high TiO 2, MgO, and Fe 2O 3 content in the soils samples from Terroirs 3 and 4 are indicative of the influence of basalt, and result from the oxidation of ferromagnesian minerals such as pyroxene, amphibole, and biotite from mafic igneous rocks like the basalt cobblestone gravels and weathered basalt bedrock present in these areas.
THE WALLA WALLA VALLEY AVA, PAG. 6 Grape Phenolic Compounds Grape phenolic compounds are classified into non-flavonoids and flavonoids. The two most wellknown non-flavonoid classes are the hydroxycinnamates and stilbenes; and the four main classes of flavonoids are the anthocyanins, flavonols (glycosides of quercetin, kaempferol, myricetin, and isorhamnetin), proanthocyanidins (condensed tannins), and flavan-3-o1 monomers (catechins), which are subunits of the proanthocyanidins (Cortell et al., 2005; Kennedy et al., 2006; Cortell and Kennedy, 2006). The average values of Brix measurements and concentrations of catechins, quercetin glycosides, tannins, total anthocyanins, and polymeric anthocyanins for the four terroirs are presented on Figure 5. The highest average Brix values correspond to the grapes from Terroir 2 vineyards. Brix is a dissolved sugar concentration measurement used to predict the potential alcohol level in wines, using an average conversion rate of sugar into alcohol. The highest average tannin and total anthocyanin concentrations are associated with the grapes from Terroir 3. Tannins contribute to the body and astringency of wines, and anthocyanins are the primary source of color in red wines. The grapes from Terroir 3 also have the lowest average catechin concentrations, indicating best seed maturity and ripeness among the four terroirs. The highest average quercetin glycosides and polymeric anthocyanins concentrations correspond to the grapes from Terroir 4 vineyards. Quercetin reacts with anthocyanins and polymeric anthocyanins are complexes of anthocyanins and tannin, both producing a more stable color through aging, aiding in the color maintenance of red wine. Figure 5: Average concentrations of grape phenolic compounds in the four terroirs.
THE WALLA WALLA VALLEY AVA, PAG. 7 Conclusion The classes and concentrations of phenolic compounds in syrah grapes collected during the 2014 harvest were compared to the soil properties at the same location for each of the four terroirs across the study area in the Walla Walla Valley AVA. Based on a preliminary evaluation, the concentrations of grape phenolic compounds are a function of the soil properties influencing the vine water status. Overall, the highest Brix values correspond to Terroir 2 vineyards (Les Collines, Leonetti Loess, and Dwelley) which are planted in silt loam soils that developed from loess parent materials. Terroir 2 consists of thick loess overlying basalt bedrock, and is characterized by soils with the highest silt content, highest SiO 2 and Al 2O 3 compositions, and lowest O.M. % and sand content among the four terroirs. The highest tannin and total anthocyanin along with the lowest catechin concentrations are associated with Terroir 3 vineyards (Ferguson and Southwind), which are planted at the highest elevations in very stony loam soils that developed from loess mixed with colluvium from basalt parent materials. Terroir 3 consists of thin loess overlying weathered basalt bedrock, and is generally characterized by well drained, low water holding capacity, shallow soils, with some of the highest CaO and MgO compositions, and the lowest Al 2O 3 content. The highest concentrations of quercetin and polymeric anthocyanin are associated with Terroir 4 vineyards (Cayuse, SJR, and Old Stones), which are planted in very cobbly loam soils developed from gravelly alluvium parent materials. Terroir 4 consists of basalt cobblestone gravels and is characterized by soils that are somewhat excessively drained, coarser textured, with low-moderate water-holding capacity, and the highest CaO, MgO, TiO 2 and Fe 2O 3 compositions among the four terroirs. Acknowledgments The authors wish to express their sincere appreciation to the Walla Walla Valley AVA winery owners, vineyard managers, and winemakers for their kindness and generosity in providing not only access to their vineyards, but very enjoyable and informative terroir discussions. LITERATURE CITED Anesi A, Stocchero M, Dal Santo S, Commisso M, Zenoni S, Ceoldo S, Tornielli GB, Siebert TE, Herderich M, Pezzotti M, Guzzo F., 2015. Towards a scientific interpretation of the terroir concept: plasticity of the grape berry metabolome. BMC Plant Biol. 15:191. doi: 10.1186/s12870-015-0584-4. Cohen, S.D. and Kennedy, J.A., (2010) Plant metabolism and the environment: Implications for managing phenolics. Crit. Rev. Food Sci. Nutr. 50, 620 643. Cortell, J. M.; Halbleib, M.; Gallagher, A. V.; Righetti, T.; Kennedy, J. A., 2005. Influence of vine vigor on grape (Vitis Vinifera L. cv. Pinot noir) and wine proanthocyanidins. J. Agric. Food Chem. 53, 5798-5808. Cortell, J. M. and Kennedy, J. A., 2006. Effect of shading on accumulation of flavonoid compounds in Vitis Vinifera L. Pinot noir fruit and extraction in a model system. J. Agric. Food Chem. 54, 8510-8520. Di Majo D., La Guardia M., Giammanco S, La Neve L., Giammanco M., 2008. The antioxidant capacity of red wine in relationship with its polyphenolic constituents. Food Chem 111:45 49.
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THE WALLA WALLA VALLEY AVA, PAG. 9 Abstract Grape phenolic compounds, which are secondary metabolites that develop in grapes during ripening are associated with grape and wine quality. The phenolic synthesis and accumulation in grapes and the resulting grape phenolic content are influenced by terroir. In particular, the vineyard soil is a key terroir element contributing a substantial control on the grapevine nutritional and water status; thus, the properties of vineyard soils influence the quality of the grapes and sensory attributes of the wine produced in that vineyard. This study presents an evaluation of the relationships between soil characteristics (parent material, depth, texture, chemistry, water holding capacity, and organic matter) and the classes and concentrations of phenolic compounds developed in syrah grapes from vineyards located in the four different terroirs of Walla Walla Valley American Viticultural Area, exploring the link between grape quality and terroir in a step toward quantifying and further deciphering the terroir effect. Keywords: Walla Walla Valley, Terroir, Phenolic Compounds, Syrah Grapes, Soil Properties