Monitoring Site-Specific Fermentation Outcomes via Oxidation Reduction Potential and UV-Vis Spectroscopy to Characterize "Hidden" Parameters of Pinot Noir Wine Fermentations.

Gordon A Walker,Maisa M M Lima,Thomas Halligan,Ron C Runnebaum,Andre Knoesen,James Nelson

doi:10.3390/molecules26164748

Gordon A Walker, Maisa M M Lima + Show 4 more

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https://doi.org/10.3390/molecules26164748

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Abstract

Real-time process metrics are standard for the majority of fermentation-based industries but have not been widely adopted by the wine industry. In this study, replicate fermentations were conducted with temperature as the main process parameter and assessed via in-line Oxidation Reduction Potential (ORP) probes and at-line profiling of phenolics compounds by UV-Vis spectroscopy. The California and Oregon vineyards used in this study displayed consistent vinification outcomes over five vintages and are representative of sites producing faster- and slower-fermenting musts. The selected sites have been previously characterized by fermentation kinetics, elemental profile, phenolics, and sensory analysis. ORP probes were integrated into individual fermentors to record how ORP changed throughout the fermentation process. The ORP profiles generally followed expected trends with deviations revealing previously undetectable process differences between sites and replicates. Site-specific differences were also observed in phenolic and anthocyanin extraction. Elemental composition was also analyzed for each vineyard, revealing distinctive profiles that correlated with the fermentation kinetics and may influence the redox status of these wines. The rapid ORP responses observed related to winemaking decisions and yeast activity suggest ORP is a useful process parameter that should be tracked in addition to Brix, temperature, and phenolics extraction for monitoring fermentations.

Highlights

IntroductionWine fermentations are typically monitored using Brix (density measurement correlated with sugar percentage) and temperature
Wine fermentations are typically monitored using Brix and temperature
While the absolute differences in fermentation times are minimal in these small volumes with well-controlled temperature, these differences would likely be more pronounced if these fermentations were conducted at a commercial production scale (>4000 L)

Summary

Introduction

Wine fermentations are typically monitored using Brix (density measurement correlated with sugar percentage) and temperature. Musts start out between ~22–26 Brix and decrease until the fermentation reaches a negative Brix value, which is due to the conversion of sugars into less dense ethanol. During the course of fermentation, the temperature generally starts low, increases due to yeast metabolism (often requiring temperature control to mitigate the deleterious effects of excess heat), and decreases in late fermentation, when yeast is less active [4]. While Brix is generally sufficient to follow fermentation progress and temperature can be used to control activity, measured changes in these parameters are generally not collected in real-time; problematic fermentations, often do not become apparent until sugar consumption by yeast has slowed or become “stuck” [6]. Process parameters for winemaking that provide insight into yeast metabolism and the changing chemical fermentation environment in real-time will be of considerable value to the industry

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