Iron

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Iron (Fe) is a transition metal that is present in trace amounts in wort and beer. It is harmful to the brewing process, mainly because even at concentrations less than 0.05 mg/L (50 ppb), it significantly increases the rate of oxidation via activation of oxygen species (e.g. Fenton reactions) and other radical reactions.[1] Iron can also directly impact flavor by contributing a blood-like metallic flavor.[2] The iron in wort and beer comes from malt during mashing, and it is also commonly present in the brewing water. The level can be further increased by other ingredients such as hops, or by extraction from poorly-passivated stainless steel brewing equipment. Minimizing the amount and activity of iron (and other transition metals) is an important component of low oxygen brewing.

Iron content in beer: Beer normally contains less than 0.2 mg iron per liter.[3][4]

Potential sources of iron[edit]

  • Grain - Depending on the malts and other factors, a standard wort has levels of around 0.1–0.3 mg/L iron.[5] The level is higher at the beginning of mashing.[6]
  • Water - Water naturally contains a trace amount of iron. In the US, the level in drinking water is regulated to be no more than 0.3 mg/L,[7] although it may be higher in private wells or other unregulated sources (which may contain iron up to around 10 mg/L).[8][9][10] The desirable level of iron in brewing water is less than 0.1 mg/L.[11][12][4] The lower, the better.[2]
  • Hops - Hops possess the highest metal ion concentration among the standard brewing ingredients; for example, Fe concentrations found were up to approximately eight times higher than in malt.[13]
  • Brewing equipment - The main component of stainless steel is iron, which can be leached into the water, wort, or beer.
  • Diatomaceous earth

During fermentation, the iron content is strongly diminished.[1]

Effects of iron[edit]

  • Increased oxidation - Iron ions are radicals that catalytically promote oxidation reactions (with or without the presence of dissolved oxygen).[3][1][11][4][14][15][13] These reactions result in a variety of negative effects, including the formation of haze, stale-tasting carbonyl compounds, increased color, gushing, etc.[16][17][11][1][4][15][13] See Oxidation and Transition metals.
  • Flavor - Iron contributes a metallic off-flavor and astringency at very low concentrations such as 0.5 mg/L in most beers, and can be detectable at less than 0.1 mg/L in more delicately flavored beers.[15][11][4][2]
  • Incomplete saccharification -[4]
  • Fermentation - Iron is an essential nutrient for yeast.[15][13] However, at concentrations over 1 mg/L, iron is harmful to fermentation.[16][4] Even at lower levels, the presence of iron can increase the production of hydrogen sulfide and other undesirable volatile sulfur compounds.[18]
  • Slime - Iron can produce slime deposits in wells and pipes when organic matter is present.[15][2]
  • Improved foam stability - may improve foam stability at 0.5 mg/L[15] Fe is also known to enhance beer foam stability (6,35)[13]

Iron salts have a negative action at concentrations above 0.2 mg/L during wort production, preventing complete saccharification, resulting in hazy worts.[4]

Ways to minimize iron[edit]

The iron content of beer should be as low as possible.[3]

  • Use tannin additives during mashing (which bind to iron and inactivate it).
  • Control the pH during mashing (lower pH increases iron extraction).
  • Use an appropriate grade (304 or 316) of stainless steel for all metal brewing equipment, and passivate it regularly (in order to minimize the amount of iron leaching from the brewing vessels and kegs, for example).
  • Use RO water instead of tap water (RO filtration effectively removes all iron from the water).
  • Do not filter beer with diatomaceous earth (because it increases iron, especially problematic at this late stage in the brewing process).

See also[edit]

Potential sources

References[edit]

  1. ↑ a b c d Zufall C, Tyrell Th. The influence of heavy metal ions on beer flavour stability. J Inst Brew. 2008;114(2):134–142.
  2. ↑ a b c d Howe S. Raw materials. In: Smart C, ed. The Craft Brewing Handbook. Woodhead Publishing; 2019.
  3. ↑ a b c Dobrinas S, Soceanu A, Gheorghiu CB, Tanase M. Comparative methods applied for the determination of total iron from beer samples. Ovidius Univ Ann Che. 2010;21(1):35–40.
  4. ↑ a b c d e f g h Filik H, Derya G. Cloud point extraction for speciation of iron in beer samples by spectrophotometry. Food Chem. 2012;130(1):209–213.
  5. ↑ Mertens T, Kunz T, Wietstock PC, Methner FJ. Complexation of transition metals by chelators added during mashing and impact on beer stability. J Inst Brew. 2021;127(4):345–357.
  6. ↑ Holzmann A, Piendl A. Malt modification and mashing conditions as factors influencing the minerals of wort. J Am Soc Brew Chem. 1977;35(1):1–8.
  7. ↑ Secondary Drinking water standards: Guidance for nuisance chemicals. U.S. Environmental Protection Agency (EPA) website. Modified February 2024. Accessed online June 2024.
  8. ↑ https://epi.dph.ncdhhs.gov/oee/docs/IronInWellWaterInfographic.pdf
  9. ↑ https://www.web.health.state.mn.us/communities/environment/water/wells/waterquality/iron.html
  10. ↑ https://www.floridahealth.gov/environmental-health/drinking-water/_documents/iron-fs.pdf
  11. ↑ a b c d Krottenthaler M, Glas K. Brew water. In: Esslinger HM, ed. Handbook of Brewing: Processes, Technology, Markets. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA; 2009.
  12. ↑ Eumann M, Schildbach S. 125th Anniversary review: Water sources and treatment in brewing. J Inst Brew. 2012;118:12–21.
  13. ↑ a b c d e Wietstock PC, Kunz T, Waterkamp H, Methner FJ. Uptake and release of Ca, Cu, Fe, Mg, and Zn during beer production. J Am Soc Brew Chem. 2015;73(2):179–184.
  14. ↑ Irwin, AJ, et al. "The Role of Copper, Oxygen, and Polyphenols in Beer Flavor Instability." Journal of the American Society of Brewing Chemists, vol. 49, no. 3, 1991, pp. 140–149.
  15. ↑ a b c d e f Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.
  16. ↑ a b Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
  17. ↑ Narziss L, Back W, Gastl M, Zarnkow M. Abriss der Bierbrauerei. 8th ed. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA; 2017.
  18. ↑ https://www.tandfonline.com/doi/pdf/10.1080/00960845.1975.12006564
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