Application of dynamic light scattering technique to detect primary gushing potential from barley to finished beer

Gushing is the spontaneous and wild overfoaming of over-carbonated beverages that occurs at the opening of the container without any shaking. Primary gushing is related to raw material contaminated by filamentous fungi. These latter produce amphiphilic proteins called hydrophobins that interact with carbon dioxide bubbles to produce overfoaming at the opening. Up to now, to determine the gushing tendency of a malt batch, most beer producers have used the Modified Carlsberg Test (MCT), where a determined volume of sparkling water is replaced by the same volume of an aqueous malt extract. However the precision and the reproducibility of this methodology have been subject to controversy. Recently a new method based on the dynamic light scattering (DLS) technique was developed in our lab to characterize the primary gushing potential of carbonated beverages. This technique was first applied only on the final product, i.e. bottled or canned beer. It appeared that the main difference between a gushing and a non-gushing beer was the presence of particles with a diameter around 100 nm only in the gushing beer. The objective of the present work was then to apply this new method on earlier stage products of the malting and brewing processes. The Congress Mash method was used to produce wort from non-contaminated and contaminated malts and from a blend of non-contaminated malt and contaminated barley. The MCT was carried out by replacing 20 mL of sparkling water from a 1 L bottle (7 g CO2/L) by 20 mL of the worts obtained from the different malt and barley samples. After three-day agitation (horizontal, 150 rpm, 20°C), the bottles were opened and the overfoaming amount was determined by weighing. The wort/sparkling water samples were then centrifuged (4,000 × g, 10 minutes) and naturally degassed (i.e. at room temperature and under atmospheric pressure) until the CO2 concentration reached approximately 1.7 g CO2/L (equilibrium value at 25°C and under atmospheric pressure). After degassing, the size of particles present in the different samples was determined by DLS. The MCT results showed that worts produced from contaminated raw material (i.e. contaminated malt or blend of non-contaminated malt and contaminated barley) had a clear gushing tendency and DLS allowed to detect the presence of particles with a diameter around 100 nm only in these gushing samples. Our results thus tend to confirm the applicability of DLS as a new method to characterize the primary gushing potential of raw materials.status: publishe