Lesson 3 - Beer Foam SAQ

** Gushing is a serious defect that will lead to customer complaints and potential product recall.

• • What are the primary and secondary causes of gushing?

  • Identify five components from the brewing process that may end up in the final beer and could cause gushing. Explain the reasons for your choices.

  • How could you reduce the chances of primary and secondary gushing in your beer?

Response:

• Gushing causes can be divided into primary and secondary causes. Primary causes are from the infection of barley (and sometimes malt) by moulds particularly those of Fusarium species. The causative agents are the hydrophobic group of proteins, the hydrophobins.

Secondary gushing is related to unintended nucleation sites in beer that give CO₂ an opportunity to break out of solution.

• Five components from the brewing process that cause gushing are:
  • Calcium oxalate
  • Metal ions
  • Diatomaceous earth
  • Packaging bottle washing surfactants
  • Over carbonation

The first three of these act as nucleation sites for rapid and uncontrolled CO₂ bubble formation and release. The carryover of surfactants from bottle washing lowers surface tension, allowing a large number of microbubbles to form when the beer is opened. These expand rapidly as they travel to the beer surface – resulting in gushing.

Over carbonation increases the supersaturation of CO₂ in beer. This leads to an unstable and rapid uncontrolled release of CO₂ when the beer is opened.

• The key to managing primary gushing is by measuring levels of DON, the marker for Fusarium. Malt high in DON is rejected by the maltster and brewer.

Good brewing practice is to precipitate calcium oxalate early in the brewing process, along with a robust quality assurance monitoring programme. This will ensure that secondary sources are eliminated.