Final Report: 2018-2022 Funding Cycle
Principal Investigator: Jim Harbertson, Associate Professor of Enology
Washington State University, Ste. Michelle Wine Estates Wine Science Center
2710 Crimson Way, Richland WA 99354
jfharbertson@wsu.edu
509.372.7506
Summary: Raman spectroscopy is a widely applied tool across several industries including textiles, pharmaceuticals, cosmetics, and homeland security, to name but a few. Despite its analytical utility, it has yet to be a widely adopted to across the wine industry. Due to this absence of reference, this primary goal of this work was to establish a baseline for both the strengths as well of the weaknesses of enological Raman analysis. A common problem with traditional or spontaneous Raman spectroscopy as it is commonly referred to is background fluorescence. As Raman spectroscopy obtains the Raman signal by means of laser excitation, the much more efficient fluorescent emission process can easily overtake the more subtle Raman signal if fluorophores such as anthocyanins found in red wines are present in the sample. Initially, it was hypothesized that fluorescence emission in each wine sample would remain constant throughout the life span of the wine and any predictive models could compensate for this baseline loss mathematically. Unfortunately, this was not the case. Over time, fluorescence emission increased over time in the red wine most likely due to the formation of polymeric pigments. This increasing baseline loss was finally resolved by extracting all phenolic compounds in the wine using polyvinylpolypyrrolidone (PVPP). With the application of PVPP, Raman spectral baseline was recovered without sacrificing the predictive power of ethanol and simple sugar predictive models in the wine. After exhaustive inquiry, it was determined that spontaneous Raman spectroscopy can greatly facilitate fermentation monitoring due to its ease of use, analytical speed, and reproducibility.
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