An understanding of factors controlling isotopic ratios of wine as a potential surrogate of past precipitation
Abstract
Precipitation, vapor water, ground water, soil water, grape berry and grape leaf water, grape must, and vintage wines were collected from northern California for stable isotopic analysis. An understanding of factors controlling isotopic ratios of wine allows evaluation of wine as a surrogate of past precipitation. Stable isotopic compositions of grape berry waters collected at Charles Krug Winery in Napa Valley, CA range from {dollar}-{dollar}31 to {dollar}-{dollar}17 per mil in {dollar}\delta{dollar}D and +7.2 to +15.3 per mil in {dollar}\delta\sp{18}{dollar}O, and plot along a transpiration line of slope 2.7. Grape leaf waters range from {dollar}-{dollar}25 to +5 per mil in {dollar}\delta{dollar}D and +0.9 to +12.4 per mil in {dollar}\delta\sp{18}{dollar}O, and plot along a transpiration line of slope 2.1. Isotopic compositions of wine range from {dollar}-{dollar}3 to +20 per mil in {dollar}\delta{dollar}D and +4.6 to +10.2 per mil in {dollar}\delta\sp{18}{dollar}O and plot along a "wine line" of slope 3.5. Similar samples collected from Concannon Vineyard in Livermore Valley, CA show similar variations as those from Napa Valley, CA; Strong correlations are observed between isotopic ratios of wine and temperature (0.94), relative humidity ({dollar}-{dollar}0.93), and ET (0.93) for approximately 1-3 months prior to harvest. The correlation with annual precipitation (0.30) suggests that amount of rainfall has nominal affect on stable isotopic ratios of wine. And compositions of wine are not expected to correlate well with the compositions of annual rainfall. The correlation observed between compositions of wine and wine quality (0.43) has no practical predictive capabilities.