In its 2018-19 fiscal year, the Oregon Wine Board of Directors granted $437,500 to researchers for nine projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let you know about the status of these projects.

Dr. James Osborne is an associate professor and enology extension specialist in the Food Science and Technology Department at Oregon State University, and is part of the Oregon Wine Research Institute. His current research focuses on the impact of wine microorganisms such as lactic acid bacteria, Brettanomyces, and non-Saccharomyces yeast on wine quality. He has prepared the update below.

Utilizing malolactic fermentation as a tool to prevent Brettanomyces bruxellensis wine spoilage

Project objectives:
The overall objective of this study is to investigate interactions between the wine spoilage yeast Brettanomyces bruxellensis (B. bruxellensis) and the malolactic bacteria Oenococcus oeni (O. oeni) in order to reduce the risk of wine spoilage.

The specific project objectives are to:

  1. Investigate O. oeni inhibition of B. bruxellensis growth and volatile phenol production and determine if strain variability exists;
  2. Determine the mechanism by which B. bruxellensis is inhibited by O. oeni; and
  3. Investigate the impact of timing of B. bruxellensis infection relative to malolactic fermentation on growth inhibition and persistence of inhibition.

Importance to the Oregon wine community:
B. bruxellensis is considered the most problematic wine spoilage yeast due to the difficulty of controlling it, the potential significant financial losses due to loss of wine quality, and the cost of prevention and remediation measures. Winemakers are limited in the tools available to prevent the infection and growth of B. bruxellensis in wine, with SO2 and sanitation being the main options. However, SO2 cannot be added to a wine until malolactic fermentation (MLF) has been completed, making the period prior to MLF a critical point where B. bruxellensis spoilage can occur.

It has been suggested that conducting a rapid MLF initiated by inoculation of O. oeni is a useful strategy to prevent B. bruxellensis spoilage, as this minimizes the length of time the wine is not protected by SO2. This project investigates an additional benefit of conducting a rapid MLF: the prevention of B. bruxellensis growth due to inhibitory interactions with O. oeni.

Progress so far:
During the first year of this study, Pinot noir wine (no SO2 additions, no MLF) was produced and used to test the ability of 13 commercial O. oeni strains to inhibit B. bruxellensis growth at the end of MLF. Sterile filtered wine was inoculated with various O. oeni strains, and O. oeni growth and malic acid were monitored. When MLF was complete, wines were inoculated with a select strain of B. bruxellensis, and its growth and volatile phenol production were monitored.

When inoculated into a wine that had recently undergone MLF, B. bruxellensis viability declined to below detectable levels. Some O. oeni strain variability was observed. For three strains used to conduct MLF, B. bruxellensis was still detectable at low populations 1-2 weeks after inoculation. For the remaining 10 strains, B. bruxellensis was not detected at any point after inoculation. Microbial populations continue to be monitored to determine how long the effect of MLF lasts.

Next steps
The sensitivity of a range of B. bruxellensis strains to O. oeni will be determined in wine using an O. oeni strain that was highly inhibitory in the previous experiment. Additional experiments will also be conducted to determine the mechanism by which O. oeni causes inhibition of B. bruxellensis growth. This information will aid in the development of strategies to better utilize MLF to reduce the risk of wine spoilage by B. bruxellensis.