Dr. Patty Skinkis, OSU Viticulture Extension Specialist, has prepared the update below. This project receives funding from the Oregon Wine Board as part of its viticulture and enology research grant program.

Importance to the Oregon Wine Community

The short- and long-term impacts of increasing or decreasing yield of Pinot noir through cluster thinning has been the focus of an Oregon State University-led research project since 2012. The project is unique, as it enlists the cooperation of commercial vineyard and winery staff who have been trained to collect data and observe the effects in their own operations. This work began after a strategic analysis of the industry yield management practices revealed narrow yield targets being applied across the state. Considering diverse vineyards and growing season variability, we began investigating the yield-quality relationship to develop yield management guidelines for Pinot noir producers across different production scales and variable seasons.

The research team is led by Dr. Patty Skinkis, OSU Viticulture Extension Specialist, who designed the project and conducts analysis of viticulture components. Dr. James Osborne, OSU Extension Enologist, developed wine production protocols and data collection metrics. Dr. Elizabeth Tomasino, OSU Assistant Professor of Enology, conducts sensory evaluations of wines through winemaker panels. Dr. Paul Schreiner, USDA-ARS Research Plant Physiologist, cooperated in data collection across a sub-set of vineyards to determine the physiological impacts of yield. Finally, Dr. McLaughlin, OSU assistant professor of statistics, conducts complex statistical models to determine impact of yield management across years and sites.


The team has collected six growing seasons of vine growth and fruit composition data, and wine sensory for four vintages. With more than 20 commercial vineyards involved in the project over the years, there is a large amount of data aggregated and being statistically analyzed. Current research results indicate the following:

  • Cluster thinning or maintaining higher yields has not changed long-term vine health parameters measured, including fruitfulness, vine nutrient status, dormant pruning weights, or yield/pruning weight ratios, suggesting that additional inputs may not be required in vineyards where higher yields are maintained.
  • Basic ripeness is often not impacted by cluster thinning except in the highest yield year (2015), where full cropped vines had slightly reduced Brix compared to those with 1 cluster/shoot or less. Cluster thinning has resulted in some differences in fruit composition. However, the differences have been variable by year and site.
  • Analysis of the long-term data from across all sites and the first five years shows that with increases in yield, there is a slight decrease in pH, total and polymeric anthocyanins, and tannins. However, TA is slightly increased. The fruit composition impact with a change in yield is not drastic, for example, our models show that for every 1 lb. /ft. increase in yield there is a decrease of 0.68 ┬░Brix. Considering that most vineyards have <1 lb. /ft. yield in any given year, the cluster thinning effect on Brix may be minimal.
  • Sensory of the 2012-2014 wines by trained professional panels show little difference for aromas, flavors and overall quality based on yield. In-house sensory evaluations are being conducted by collaborating wineries to provide more in-depth sensory perception results within their production context.
  • Overall, results are showing that yield targets can be increased without compromising quality. The work is not suggesting that no thinning is required, rather, most collaborators are confident that a modest increase will not result in quality loss. The 2017 data will be analyzed with the prior five years to further refine our guidelines. We will also be focusing on impacts of site on the yield-quality relationship, including the effects of vine nitrogen status, seasonal heat units/air temperature, and possibly soil properties (e.g. soil moisture).

This research has been funded in part by the Oregon Wine Board, OWRI Pilot Project Funds, and Extension Program funds generated by the lead PI. This work would not be possible without the support of the many industry collaborators who have devoted significant resources of time and labor to the project.