Retention of Iron and Copper during Mashing of Roasted Malts

Abstract

Malt is the major source of iron (Fe) and copper (Cu) in wort and beer, and the main uptake of Fe and Cu ions happens during mashing. Past research has indicated that the mineral composition of sweet wort primarily depends on the ion removal rate during mash filtration. In this study, the capacity to remove Fe and Cu during mashing has been evaluated. Each metal was added (50 µM) at the beginning of congress mashings and the final concentrations in sweet wort were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). There was little to no difference between the samples spiked with Fe and the blanks when using pure pilsner malt, suggesting that there is an efficient binding of Fe in the spent grains. A significant, but not complete, removal was also observed for Cu-spiked samples. Mashing with roasted malt showed decreased removal of Fe while removal of Cu was increased. The effects of addition of high metal concentrations during mashing on the oxidative stability of the sweet wort were evaluated using electron spin resonance (ESR) spectroscopy and oxygen consumption. It was concluded that the spent grains have an important leveling effect on the final Fe and Cu concentrations in sweet wort, which also levels the effects on oxidative reactions.