Gushing

Gushing is a defect of beer in which violent, uncontrolled foaming erupts when bottles or barrels are opened, often expelling a large share of the contents. It is associated with the formation of calcium oxalate crystals in the beer, which provide nucleation sites for dissolved CO₂, and with contamination of malting barley by Fusarium graminearum, whose hydrophobin proteins stabilise foam excessively. Brewers prevent gushing through careful barley selection and storage, adequate malt cleaning, control of calcium oxalate precipitation, and filtration or stabilisation treatments. Because gushing ruins presentation and causes commercial losses, maltsters routinely test barley lots for Fusarium infection and gushing potential before acceptance.