Study of the adhesive properties of Chimay’s brewer yeast using AFM

Details

Supervisors

Alsteens, David

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

The brewery of the Chimay beer faces an issue stemming from yeast deposits formed at the bottom of the beer bottles. Chimay Brewery asked UCLouvain's nBio lab (LIBST) to study this phenomenon and identify potential solutions. This master's thesis focused on analyzing the yeast deposit formation and detachment observed by the Chimay Brewery and, more specifically, the adhesive properties of Chimay's yeast as well as its mechanical properties. The objectives of this thesis were (i) to acquire a better understanding of the phenomenon in question, (ii) to assess the adhesive and mechanical properties of Chimay’s yeast, and (iii) to investigate the potential origins of the phenomenon. Several analytical methods have been used, including the atomic force microscopy (AFM) as well as other surface characterization methods. Optical analyses performed on yeasts from two samples used by Chimay for, respectively, the main fermentation and refermentation allowed to reveal the main difference between these samples. On another note, the correlation between the composition and the hydrophilicity of the bottom surface of the bottles suggested (i) the presence of potential contaminations over the surface of new bottles, and (ii) that washing the beer bottles with KOH efficiently removes the organic compounds before recycling the bottles. At the core of the issue analyzed in this master’s thesis, the ability of Chimay’s yeast to establish hydrophobic interactions was highlighted, and these interactions appear to have a significant driving force for the yeast adhesion. The assessment of the yeast mechanical properties showed two different tendencies for yeasts from, respectively, the exponential and the stationary growth phase. The investigation of the KOH washing of the bottle showed that it has no impact on the occurrence of cell lysis which was assumed to be a potential origin. Further research should focus on the potential role of calcium as a key element to deal with yeast adhesion mechanisms.