Final Report: This is year 3 of a 3 year project for the Washington Grape & Wine Research Program
Date: January 31, 2014

Project Title: Phenolic Management: Investigation of Deficit Irrigation Severity, UV-Vis Modeling and Tannin Protein Binding Capacity

Principal Investigator: James F. Harbertson, Ph.D., Associate Scientist, Research Enologist
Organization: School of Food Science, Washington State University
Address: IAREC, 24106 N. Bunn Road, Prosser, WA 99350-8694
Telephone: 509-786-9296
Fax: 509-786-9370


  • Markus Keller, Ph.D., WSU Prosser. Dr. Keller will provide consultation and advisement on measuring and recording vineyard parameters described below.
  • Russell Smithyman, Ph.D., Ste. Michelle Estates. Dr. Smithyman will provide access to the vineyards, vineyard data (irrigation logs, climate data).
  • William Riley, Ph.D., Ste. Michelle Estates. Dr. Riley will provide access to the vineyards (for both experiments), vineyard data (irrigation logs, climate data).
  • Thomas Henick-Kling, WSU Tri-Cities. Dr. Henick-Kling will provide expertise for sensory evaluation of wines.
  • John Thorngate, Ph.D., Applications Chemist, Constellation Wines U.S. Dr. Thorngate will be responsible for modeling of phenolic analysis.
  • Mark Downey, Ph.D., Group Leader, Plant Production Sciences, Senior Research Scientist, Viticulture & Oenology, Mildura Australia.
  • Hildegarde Heymann, Ph.D. Professor, UC Davis, Dr. Heymann’s laboratory will provide consultation for wine produced sensory analysis of fruit maturity trial.

I. Project Summary(s): Objectives:

  1. Impact of deficit irrigation severity on grape and wine composition. Situation: All vineyards in Eastern Washington are irrigated due to its arid climate, which in some areas receives less than 10 inches of rainfall annually. Due to the expense of water usage many vineyards are evaluating the use of regulated deficit irrigation to either improve the wine or alter the wine style. Both timing and severity of regulated deficit irrigation are unknown areas of research with regards to altering wine composition and quality. Objective 2: The assessment of phenolics during the winemaking process has proven itself to be a worthwhile endeavor. Wineries around the world have been using phenolic analysis during winemaking to help make winemaking decisions. Several analytical techniques exist however my laboratory’s work has been instrumental in the development of the so- called “Harbertson-Adams” assays for important classes of phenolic compounds. The Harbertson-Adams assays measure functional classes of phenolic compounds; however, the methodology is both labor- and time-intensive. Objective 3: Seed tannins are largely believed to be problematic by winemakers who believe that longer ripening and higher ethanol concentrations in the must contribute to altering the extraction of seed tannins during red wine production. Winemakers believe that seed tannins give red wines a harsh astringency whereas tannins from the skin are more palatable. In model studies it has been shown that seed tannin extraction declines during grape ripening whereas the same model studies demonstrate that greater ethanol concentrations increase extraction of seed tannins. Thus winemakers believe if they wait longer for grapes to ripen they can reduce seed tannin extraction. However as the more ripe fruit will potentially yield a greater alcohol concentration and potentially more seed tannin extraction there remains a conundrum.
  2. Although there are several different objectives here we maintain the same approach for extension related activities. Our work is disseminated through talks with local wine and winegrape grower related meetings by oral presentations, posters or discussions with winemakers or grape growers. The work is also presented at the national level by presenting at the American Society of Enology and Viticulture National Conference. Our work is also summarized in trade magazines, extension briefs or through a newsletter edited by my viticulture extension colleague. We use basic extension surveys for our events and include learning based objectives and questions to determine the value of our work.
  3. Ultimately the project was designed to provide better information to winemakers and growers about the impacts of deficit irrigation, and grape maturity on grape and wine phenolic composition. The project was also designed to create a model that could be used to predict the phenolic composition of a sample by gathering spectra in the ultra violet and visible wavelength region without having to carry out the entire wet chemistry method.

Read more by downloading the full report above.

Enology // Irrigation // Phenolics //