Profiling and comparison of five bottled refermented handmade beers analyzed by comprehensive twodimensional gas chromatography time-of-flight mass spectrometry

Fermented beverage, such as beer, are considered as complex mixtures by flavor and food chemists. The beer volatolome contains hundreds of compounds, which affect the taste and the mouthfeel. In this highly competitive market, it is crucial for brewers to master each step of the process to understand and control the taste and to guarantee aroma quality and stability. Aroma compounds are essentially derived from the raw ingredients and the conditions used to produce beers, including the fermenting yeast strain. This study aims to determine the impact of the yeast on beer’s volatolome. More specifically, the impact of yeast used for bottle fermentation.
On microbrewery set-up, we brewed 5 different beers with the same feedstock and fermenting yeast. During the bottling, we used 5 different yeasts generally used by brewers. After an aging period of 8 weeks, all samples were analyzed using solid-phase microextraction couple with comprehensive two-dimensional gas chromatography coupled to mass spectrometry (SPME-GC×GC-TOFMS). A dedicated data processing workflow was then optimized. Principal component analysis (PCA) was used to visualize the clustering between sample types. The resulting clusters were compared with classical beer quality metrics, such as isoamyl acetate and polyphenols concentrations. After data curation, peaks area of VOCs founds in each beer were used to carry out unsupervised statistical analyses. Two distinct groups were observed on PCA; two beers are considered very similar regarding the VOCs while the remaining three constitute the second cluster. Based on these results, the aroma profiles of the different beers could be dressed. While the group of two beers was dominated by ethyl esters giving fruity aromas, less associated fruity fragrance esters were expressed in the other group.
The beer aroma profile was impacted by the yeast strain used for the bottle fermentation. Specific esters were produced, resulting in beer-type classification on PCA.