Stainless steel flavour contribution to beer.

Olsson, H. Parra, J. and Ragno, J.

Abstract
Metallic flavour from stainless steel has long been a problem and it is necessary to passivate the steel to prevent this. Previously this was done by pickling the metal in beer but this process was costly and slow. Experiments have been carried out on different chemical passivation techniques using cirtic, sulphamic, tannic or phosphoric acids, and a successful process has been developed which is described. Citric acid, a powerful chelating agent, when used at 70 degrees C and 4% by weight concentration, chemically complexes metallic ions on the surface of the stainless steel, and sequesters the metallic ion chelates. Soluble chelates are then removed by rinsing. The stainless steel surface is thus passivated such that beer can contact the surface for more than 70 days without picking up metallic flavour.
Keywords: beer metallic flavour pilot plant trial stainless steel