Examining Regional Trends in Pennsylvania Grüner Veltliner Wines Using Instrumental and Human Sensory Methods
Open Access
- Author:
- Keller, Stephanie
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 29, 2020
- Committee Members:
- Ryan John Elias, Thesis Advisor/Co-Advisor
Helene Hopfer, Thesis Advisor/Co-Advisor
Michela Centinari, Committee Member
Robert F Roberts, Program Head/Chair - Keywords:
- Grüner Veltliner
White Wine
Wine Regionality
Pennsylvania
Descriptive Analysis - Abstract:
- It is often said that high quality grapes must be used in order to create high quality wines. This production begins in the vineyard and is impacted by viticultural and environmental conditions that may or may not be able to be controlled. Weather conditions are among these uncontrollable factors, and the influence of weather conditions on final grape and wine quality has been the subject of investigation in both research and industry for many years. Many studies have determined that factors such as rainfall, sunlight exposure, and temperature play an important role in the development of phenolic and aromatic compounds and their precursors in berries, which ultimately affects wine aroma, taste, and flavor. Examination of weather conditions and climate in wine regions have been the subject of studies not only to understand impacts on wine quality attributes, but also to determine if regional trends exist for particular areas. The concept of regionality, or the particular style of wine that a growing region produces, is a new area of study for the Eastern United States, including Pennsylvania, which is the focus of this study. Determining regional characteristics can assist growers in predicting the quality of grapes before harvest and can also identify viticultural and sensory factors that can improve marketing strategies to wine consumers. Grüner Veltliner (Vitis vinifera; GV), an Austrian grape variety, is a relatively new grape to wine growers and producers in the northeast United States including Pennsylvania (PA). While climatic conditions are favorable to its growth, the PA wine industry is still becoming familiar with the varietal characteristics of GV grown and produced across the state. The aim of this study was to characterize the chemical and sensory factors that drive regional differences in PA GV wines through a controlled winemaking study. GV grapes were harvested from experimental sites in four PA growing regions over two vintages. A total of 9 sites were chosen in order to capture climate variability of the growing regions and to be representative of the various regions that currently grow GV in PA – two in the Northwest (NW), one in the North Central region (NC), one in the Northeast (NE), and five in the Southeast region (SE). Weather data was collected from each site during both growing seasons as well. Wines were vinified using a standard vinification method to eliminate the influence of winemaking style on samples. Chemical analysis included headspace solid phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS), high performance liquid chromatography (HPLC), and color analysis using CIE-Lab. Descriptive analysis was used to evaluate aroma, taste, mouthfeel, and flavor intensities in wines vinified from each experimental site. Finally, Pearson’s correlation was used to examine if any relationships existed between sensory and instrumental variables. Two descriptive analysis panels (one for each year of study) found significant differences (p < 0.05) in multiple aroma, taste, and flavor attributes. In Year 1, regional differences were found in yellow color and haziness, with the NW region produced wines rated highest in yellow color and lowest in haziness. In Year 2, regional differences were found again in yellow color and haziness, as well as in green apple, citrus, and thiol flavor; thiol aroma; sour, sweet, and salty taste; and astringent mouthfeel. NW wines were again highest in yellow color, while the SE region produced wines highest in thiol aroma and flavor in both years of study. In Year 2, NW wines were highest in citrus and green apple flavors, as well as sour taste, which may be due to the higher acidity in grapes at harvest from this region. Aroma analysis found regional differences in the concentration of a number of aromatic precursors in both juice and wine samples. Some differences in wine aroma profiles were likely due to higher concentrations of aroma precursors, such as hexyl acetate in NC wines. Significantly different volatile compounds did not necessarily align with the significantly different aroma attributes found in descriptive analysis. There were not regional differences in concentrations of phenolic compounds, namely (+)-catechin, (-)-epicatechin, and gallic acid, except in Year 1 where NC wines were lower in (-)-epicatechin content than the NW and SE regions. CIE-Lab color analysis showed similar results to panelist appearance ratings; NW wines were higher in b*, indicating the wines were more yellow in color than those from other regions. A number of significant positive and negative linear correlations (p < 0.05) were found when examining sensory and chemical variables together. In both years of study, yellow color ratings were positively correlated with b* and negatively with a*. Sour taste was positively correlated with titratable acidity and negatively correlated with pH. Other correlations between aroma compounds and aroma attributes were found, and while these correlations do not prove causality, these can give insight into which relationships should be further studied. Overall, this study successfully identified regional differences in PA GV wines using both sensory and instrumental methods. Since winemaking was controlled in this study, thus eliminating variation in winemaking style that can be found in commercial GV, differences in appearance, aroma, and flavor are likely due to differences in weather conditions across growing regions. Further work is necessary to relate climatic conditions to final wine composition, and a third year of study is planned to provide further insight into regional climatic differences and drivers of regionality in GV. Results of this study unveiled key sensory attributes of PA GV, which will be useful for wineries and their tasting room staff to market GV wines to consumers and increase recognition of the variety as it becomes more popular with producers in the state.