Primary versus secondary gushing and assay procedures used to assess malt/beer gushing potential.

Casey, G.P.

Abstract
The causes and prevention of beer gushing are discussed on the basis of a review of the literature. The author distinguishes between "primary" gushing, associated with the use of malt made from barley (or wheat) contaminated by mould fungi, especially certain species of the genus Fusarium, and presumed to be caused by some substance (still unidentified at the time of writing) produced either by the mould or by the effects of mould infection on the barley grain's own biochemistry, and "secondary" gushing caused by solid particles or adsorbed gas residues acting as nuclei for bubble formation, which may arise from various sources (dust contamination of containers, faulty filtration, haze particles developing in aged beer, etc.). In primary gushing, the bubble nuclei are composed of a surface active material (thought to be the unknown mould product) forming a pellicle enclosing some carbon dioxide gas. While agitation is necessary to trigger primary gushing, and it can be controlled to some extent by repasteurizing or chilling the remaining containers in an affected batch of beer, the only reliable means of prevention is to avoid the use of mould contaminated barley in malting and brewing. Methods for evaluating the likelihood of gushing on the basis of malt, wort or beer analyses are described. While most of these involve the physical testing of malt extracts, worts or beers after treatments intended to accelerate the development of the gushing factor if it is present, the Carlsberg Brewery in Denmark subjects barley and malt samples to a selective plating procedure to detect Fusarium contamination, and the brewery's scientists have also developed an enzyme linked immunosorbent assay (ELISA) test kit for detecting antigens arising from the current or former presence of Fusarium (although it is pointed out that some species in other mould genera, e.g. Aspergillus, can also cause primary gushing, but would not be detected by this test). The presence in malt of ergosterol and/or of the mycotoxin deoxynivalenol (DON), which are products of mould infection, is regarded by the author as the most reliable indicator (though still not as reliable as the industry requires) of a possible propensity towards gushing.
Keywords : analysis barley beer contamination fungi gushing malt prospect wort