Production and Management of Aroma Compounds by Dekkera/Brettanomyces Isolated from Wine

The yeast Dekkera/Brettanomyces is commonly found in wines and is responsible for a
wide array of characteristic odors. The aim of this project is to define the role of substrate
availability and physical growth factors in production of desired and undesired aroma
compounds. A practical aim is to determine the impact of nutrients, particularly those
that may be added in the wine making process that may result in off-character formation
by Brettanomyces. The isolates of Brettanomyces were grown in a defined medium
supplemented with aromatic amino acids or phenolic compounds to determine what
substrates might produce specific aroma associated chemical compounds. Initially we
looked at the compounds that were common to most of the five strains that were grown
with the added substrates.

In a defined medium the range of aroma-associated compounds produced by
Brettanomyces was very broad. The variety of compounds produced by the
Brettanomyces strains without supplementation included many of the same aroma
compounds associated with Saccharomyces. The compounds produced specifically in the
defined medium supplemented with the amino acids and organic acids belonged to
several different classes. We found higher alcohols, fatty acids and their esters, volatile
phenols, terpenes, and an aldehyde and a carboxylic acid. The volatile phenols were
associated with the organic acid supplements while the fatty acids and their esters were
primarily associated with amino acid supplements. The other compounds did not seem
to give any such specific correlations.

We have grown three Brettanomyces bruxellensis strains under three levels of oxygen, 0,
25, and 50% air saturation. Preliminary results indicate that there is some production of
4-ethylphenol (4-EP) from coumaric acid even under 0% air when growth is severely
limited. One of the strains shows a different pattern of sensitivity to oxygen than the
other two strains. While two of the strains produce the same amount of 4-EP at 25 and
50% air saturation the third strain produces only about half the 4-EP at 25% air saturation
that is does at 50% air saturation.