G. S. Derdelinckx (1), M. POSTULKOVA (2), K. Cordova (3), D. S. Riveros Galan (4), H. Verachtert (1), K. Gebruers (5), S. Smet (6), S. M. Deckers (7), H. Neven (8);
(1) KULeuven-FBIW-LFoRCe-M2S-LiBR, Heverlee, Belgium; (2) KULeuven-FBIW-LFoRCe-M2S-LiBR, Heverlee, Czech Republic; (3) KULeuven-FBIW-LFoRCe-M2S-LiBR, Heverlee, Mexico; (4) KULeuven-FBIW-LFoRCe-M2S-LiBR, Heverlee, Colombia; (5) KULeuven-FBIW-LFoRCe-M2S-CLMT, Heverlee, Belgium; (6) KULeuven-FBIW-M2S-COK, Heverlee, Belgium; (7) Brewery of Orval, Florenville, Belgium; (8) Brewery Duvel/Moortgat, Breendonk, Belgium
Primary gushing of beer is basically most often related to microbial contamination of raw materials such as barley and malt by typical fungi. Moreover it has been demonstrated since 2006 that, depending on the mold involved, the amount of the proteins (the class II hydrophobines) responsible for primary gushing (expressed in volume) is variable. However it remains to be underlined that the major responsible molecule of “primary gushing” is in fact CO2 (as also for “secondary gushing”). After opening of a bottle (decapping), the overfoaming (liquid expulsion) by “primary gushing” occurs in two phases: at first, over-pressurized nanobubbles (nanobombs) contain CO2 and they explode. This generates shock energy which reaches the glass wall of the bottle. This phenomenon was studied by Rodriguez who showed that the hydrogen bonds (low energy) between CO2 and beer can be disrupted consecutively to a developing cavitation movement. Finally, after the onset of this reaction the quantity of liquid expelled out of the bottle represents the difference between the energy liberated by the cavitation, the resistance of the hydrogen bonds, and the volume taken by the liberation of the CO2 under gaseous form! Quantitatively (regarding the volume of the bottle), the latter is clearly the most important. Qualitatively, it would be a good improvement to reduce gushing should it be possible to improve (increase) the binding between CO2 and the beer matrix in a beer susceptible to primary gushing. This link is in fact under the governance of the law of Henry and more precisely of the constant “k.” This constant varying in function with temperature (!) establishes the solubility of gaseous CO2 in liquids in function with the pressure. As indicated, the bonding between CO2 and water is based on van der Waals forces and lowering the temperature can play an important role by helping the stability of the structure. In specialty beers with a complex structure, CO2 can be more or less linked depending on the raw materials that are used by the recipe. In those beers, also depending on the brand characteristics (ale or lager for example), the use of an identical malt can be done without risks or provoke detrimental consequences after selling the beer. This all depends on the consumption (dispensing) conditions and on the aspects of the constant of Henry.
Michaela Postulkova (born 1987) holds an M.S. degree in biotechnology (2012) obtained at the University of Chemistry and Technology (UCT), Prague. She has been studying brewing and malting technology with a focus on the problem of gushing in beer. Michaela has been pursuing a Ph.D. degree in the Department of Biotechnology (UCT) in the group of Assoc. Prof. Branyik since 2012, and in 2013 she started working at the Czech Academy of Science, in the Institute of Chemical Process Fundamentals. Since 2014, she has been an intern in the group of Prof. Derdelinckx in KU Leuven, Belgium. Her field of studies is two-phase systems, which includes foam and foaming, with special attention on gushing in beverages.