Metal ion concentrations affect the success of beer brewing. While the presence of some minerals is crucial during mashing and fermentation, Cu and Fe generally have a negative impact on the oxidative stability of the final beer. Malt is the biggest source of metal ions; therefore, the main uptake of Fe and Cu ions happens during mashing.
Past research has indicated that the ionic composition of sweet wort primarily depends on the ion removal rate during mash filtration. Malt modification by roasting increases the sweet wort levels of Fe and decreases Cu. In this study, the capacity to remove Fe and Cu during mashing has been evaluated. 50 µM of each metal were added in the beginning of the EBC mashing procedure and the final concentrations in sweet wort were determined using inductively coupled plasma optical emission spectroscopy.
There was little to no difference between the samples spiked with iron and the blanks when using pure pilsner malt, suggesting that there is an efficient binding in the spent grains. Copper-spiked samples exhibited a significant decrease in concentration. Roasting decreased the removal of Fe while increasing the removal of Cu. The effect of higher metal concentrations during mashing on the oxidative stability of the sweet wort was evaluated using electron spin resonance 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, and that this effect depends on the malt’s degree of roasting.