We tentatively have identified potential aroma producing compounds that are made by the five different Brettanomyces isolates without the specific substrate added. These results can be interpreted as the production of compounds that are not affected by substrate availability. Most of the isolates produced the fruity compound, ethyl acetate, without additional substrate but only strain 2058 produced 2-methyl-butanoic acid, described as sweaty. Strain 2082 was the only one to produce the isoamyl alcohol (cleaning fluid) and isoamyl acetate (banana) compounds with no additional substrate added. Strain 2091 was the only one to produce ethyl laurate, a soapy compound, in the defined medium alone.
Adding the different substrates allows us to define some compounds that are affected by substrate as well as a group that are specific to a combination of substrate and Brettanomyces strain. For example, 4-ethylphenol and 4-vinylphenol production are characteristic of the coumaric acid substrate, while isovaleric acid was characteristic of tryptophan addition. Some compounds were produced by specific isolates only in the presence of a certain substrate. For instance strain 2091 only produced 2-methylbutanoicacid in the presence of phenylalanine.
Addition of amino acids to wines inoculated with Brettanomyces appears to have little or no affect on the growth of the yeast. We were able to determine numbers of cells by QPCR even though the cells of strain 2091 did not grow on plates. This may indicate that the cells were in a viable but not culturable state or that the QPCR detected cells that were not living. If we are able to detect products of metabolism in the wines where we could not plate the Brettanomyces it could mean that the cells are still capable of metabolism even if they cannot grow on the plating medium.