In its 2019-20 fiscal year, the Oregon Wine Board of Directors granted $417,000 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 Department of Food Science and Technology 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 (or “Brett”) and the malolactic bacteria Oenococcus oeni in order to reduce the risk of wine spoilage.

The specific project objectives are to:

  • Investigate how oeni inhibits Brett growth and volatile phenol production and determine if strain variability exists
  • Determine the mechanism by which Brett is inhibited by oeni
  • Investigate the impact of timing of Brett infection relative to malolactic fermentation on Brett growth inhibition and the persistence of Brett inhibition

Importance to the Oregon wine community:
Brettanomyces 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 Brett 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 this time period a critical point where Brett spoilage can occur.

It has been suggested that conducting a rapid MLF initiated by inoculation of O. oeni is a useful strategy to prevent Brett 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 Brett growth due to inhibitory interactions with O. oeni.

Progress so far:
Process
Pinot noir wine (no SO2 additions, no MLF) was produced and used to test the ability of a large number of commercial O. oeni strains to inhibit Brett growth at the end of MLF. Sterile filtered wine was inoculated with one of 11 commercial O. oeni strains and Brett growth and malic acid levels were monitored. When MLF was complete, the wines were inoculated with a select strain of Brett and growth and volatile phenol production were monitored.

Findings
Compared to the control, Brett growth was inhibited in wines that had undergone MLF no matter what strain of O. oeni was used. O. oeni strain variability was observed, however, with some strains so strongly inhibiting Brett that populations were not detected throughout the experiment. Other strains inhibited Brett growth to a lesser extent.

The sensitivity of a range of Brett strains to one select O. oeni strain was also determined. While B. bruxellensis UCD2049 populations declined rapidly when inoculated into wine that had just completed MLF with O. oeni, growth of the other Brett strains tested was not impacted. Why  strain UCD2049 is more sensitive to O. oeni than the other Brett strains tested is unknown at this point. One possibility is that the inhibition of Brett by O. oeni is influenced by wine conditions such as pH and ethanol as Brett strains vary in their sensitivity to these wine parameters. Experiments will be conducted to determine whether this explains the observed variation between strains.

Next steps:
Additional studies are underway exploring how the timing of Brett infection relative to MLF affects inhibition by O. oeni. The mechanism of inhibition is also being investigated to determine if inhibition occurs via cell-to-cell contact, nutrient depletion, or production of an inhibitory compound by O. oeni. While wineries must continue to use sound winemaking practices to prevent the growth of Brett, results from this study may aid in the development of strategies to better utilize MLF to reduce the risk of wine spoilage due to Brett.