Contribution of 3-methylthiopropionaldehyde to the Worty Flavor of Alcohol-free Beers

Alcohol-free beers are usually criticized for two major defects: a lack of fruity aroma and a strong worty flavor. 3-Methylbutanal and 2-methylbutanal are described in the literature as being predominantly responsible for the worty taste. Although detected in large amounts in most malt and wort extracts, both compounds have proven unable to confer worty taste to beers. In this work, we extracted volatiles from wort with a Likens-Nickerson microextractor. The resulting extract had a strong worty aroma. Following GC/MS and GC/olfactometry analysis, 3-methylthiopropionaldehyde turned out to be the key feature since it remained the most organoleptically active compound through extract dilution. In vitro assays showed that 3-methylthiopropionaldehyde is a substrate for several Saccharomyces cerevisiae reducing enzymes. Screening of various strains led us to conclude that the higher the 3-methylbutanal reductase activity, the higher the 3-methylthiopropionaldehyde reductase activity. Monitoring of 3-methylthiopropionaldehyde concentration through an in vivo cold contact process has also been undertaken.