Dark Beer Richer in Iron Than Pale Beer

According to the analysis carried out by the University of Valladolid (UVa) on 40 types of beers from all 5 continents, dark beers have an average free iron content of 121 ppb (parts per billion) compared to 92 ppb in pale beers and 63 ppb in non-alcoholic beers. 

After analyzing 40 brands of beer, a team of researchers from the University of Valladolid (Spain) have discovered that dark beer has more free iron than pale and non-alcoholic beers. Iron is essential to the human diet, but also helps oxidize the organic compounds that give these beverages stability and flavour.

"Although these quantities are very small, the differences are apparent and could be due to the production processes or raw materials used in manufacturing," stated Carlos Blanco, professor of Food Technology at UVa and co-author of the study.
The study, published in the Journal of the Science of Food and Agriculture, indicates that higher iron content in dark beer could be explained by the malt and hop extracts used to produce it.
However, pale beer production includes a filtering stage in which diatomaceous earth is used. This sedimentary rock is a porous material with micro-algae used to lighten the beer; it traps the iron, causing its concentrations to decrease.
Non-alcoholic beer undergoes vacuum evaporation processes to remove the alcohol. This operation also removes iron ions given that they are dragged by the volatile molecules.