Iron oxidizes the organic compounds that give beers their stability and flavor so it has an influence on the beer brewing process, affecting taste, growth of yeast, and foaming quality.

Carlos Blanco and colleagues, University of Valladolid, Spain, have analyzed 40 brands of beer and discovered that dark beer has more free iron than pale and non-alcoholic beers. On average, dark beers contained 121 ppb (parts per billion) of iron compared with 92 ppb in pale beers and 63 ppb in non-alcoholic beers.

The team writes that the higher iron content in dark beer could be from the malt and hop extracts used to produce it, while much of the iron in light beers is trapped by the filtering process used to lighten the beer. Non-alcoholic beer undergoes vacuum evaporation to remove the alcohol which also removes iron.

• Free iron in pale, dark and alcohol-free commercial lager beers
  D. Sancho, C. A. Blanco, I. Caballero, A. Pascual,
  J. Sci. Food. Agric. 2011, 91(6), 1142—1147.
  DOI: 10.1002/jsfa.4298