Final Report: This is a completed project for the Washington Grape & Wine Research Program
Date: 30 June 2018

Title: Microbiology and Chemistry of Washington Wines
Project Duration: 2015-2018
Principal Investigator: C.G. Edwards
Organization: School of Food Science, Washington State University, Pullman, WA 99164-6376
Telephone: 509-335-6612

WRAC Project Number: 3057-5522

Cooperator Name: B. Bondada
Organization: Washington State University
Description of participation: Student committee member

Cooperator Name: C.F. Ross
Organization: Washington State University
Description of participation: Sensory methods development/student committee member

Cooperator Name: G. Unlu
Organization: University of Idaho
Description of participation: Microbial physiology/student committee member

Project Summary:

The yeast, Brettanomyces bruxellensis, spoilage is a concern, if not a major threat, to red wine quality. Additional research regarding those factors that impact its growth and ability to survive under various conditions would allow for prediction of high-risk situations as well as development of effective control measures. Thus, this project evaluated the ability of this yeast to survive in winery waste (e.g., pomace) sometimes spread in vineyards over a lengthy storage time (>1 year).

A major vector for B. bruxellensis has been oak barrels. Given the porous nature of wood, the yeast can penetrate staves such that the effectiveness of methods for cleaning and sanitizing are questionable. During this project, new barrels were infected with strains of B. bruxellensis originally obtained from Washington wines. After a lengthy storage with wine, the barrels were drained and taken apart to determine the penetration depth of the yeast as well as impacts of such sanitizing protocols as steaming or hot water on recovery of viable cells. Results from this project have yielded suggested times/temperatures for removing the yeast from oak barrels.

Worldwide, some winemakers are purposefully encouraging the growth of non-Saccharomyces yeasts present on grapes to improve such sensory parameters as ‘mouthfeel.’ More recently, researchers in Australia have reported success in reducing alcohol concentrations by using sequential fermentations, i.e., inoculation with selected non-Saccharomyces species followed by addition of Saccharomyces. While winemakers can rely on native yeasts to provide unique and desirable sensory qualities, there is a risk to quality if undesirable non-Saccharomyces yeasts dominate fermentation. In addition, non-Saccharomyces are being investigated to lower final ethanol concentrations wines. Here, many of these yeasts will utilize fermentable sugars without production of ethanol thereby lessening the amount of sugar Saccharomyces needs to ferment to achieve dryness.

Project Major Accomplishments:


  1. Brettanomyces spoilage of wines.
    • Continue to examine whether new technology (so-called “electronic tongue”) can be used for detection of Brettanomyces spoilage.
    • Evaluate seasonal survivability of the yeast over time in grape pomace samples located in Washington State vineyards.
    • Assess the effectiveness of physical treatments to eliminate the yeast at different depths in oak barrel staves that differ by oak type and toasting level.
  2. Impact of non-Saccharomyces yeasts on wine quality.
    • Ability of sequential inoculations of non-Saccharomyces and Saccharomyces as a means to lower final alcohol yield.
    • Evaluate nitrogen and sugar utilization of sequential inoculations of non-Saccharomyces and Saccharomyces yeast during aerated and non-aerated growth.
    • Determine impact of non-Saccharomyces yeast on mouthfeel due to increased solubility of pectins.

Read more by downloading the full report above.

Enology // Yeast //