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 extr acts, both compounds have proven unable to confer worty taste to beers. In this work, we extracted volatiles from wort with a Likens-Nickerson microex tractor. The resulting extract had a strong worty aroma. Following GC/MS an d GC/olfactometry analysis, 3-methylthiopropionaldehyde turned out to be th e key feature since it remained the most organoleptically active compound t hrough extract dilution. In vitro assays showed that 3-methylthiopropionald ehyde is a substrate for several Saccharomyces cerevisiae reducing enzymes. Screening of various strains led us to conclude that the higher the 3-meth ylbutanal reductase activity, the higher the 3-methylthiopropionaldehyde re ductase activity. Monitoring of 3-methylthiopropionaldehyde concentration t hrough an in vivo cold contact process has also been undertaken.