In European countries, gushing appears to be associated primarily with defects in malt quality, in particular, growth of certain moulds on the barley either before harvest, during storage or during malting (see, for example, this Journal, 1976, 82, 182 and 350). This type of gushing (summer-type) is apparent immediately after bottling and diminishes during storage. In contrast, gushing in the USA, Canada and Japan, where beer is drunk chilled to low temperature, seems to occur mainly when the beer is shaken or stored at temperatures around 0oC before opened at room temperature. This type of gushing (winter-type) has been ascribed to the presence of various heavy metal ions (Fe, Sn, Ni and Co) or to microcrystals of calcium oxalate. Incidences of winter-type gushing in the authors' brewery were not attributable to these factors and it was shown that gushing potential developed during storage for 1 to 3 months. Gushing was enhanced by storage at 0oC for up to 72 h before opening, especially if stored in a horizontal position. A survey of beers for gushing potential showed that those having residual proteolytic activity were prone to gushing whereas those with no residual activity were not. Pilot brewery trials confirmed that addition of papain or other cysteine proteases (bromelain, ficin) caused gushing. Denatured or inactivated enzyme did not promote gushing, showing the effect was associated with the proteolytic action on beer proteins. Several types of acid protease from microbial sources were effective in reducing the gushing potential of aged beer and the combined use of a small amount of acid protease with papain effectively suppressed gushing potential without impairing beer quality. These findings suggest that the acid proteases, which are able to cleave peptide bonds not attacked by papain, hydrolyze peptide bonds not attacked by papain, hydrolyze peptide gushing factors (or their precursors) produced by the action of papain.
Keywords: beer bottle chillproofing enzyme gushing proteolysis