Copper

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Copper (Cu) is a transition metal extracted primarily from malt during mashing, but it is also commonly present in the brewing water. Copper can also leach into the wort or beer from copper or brass brewing equipment (e.g. copper manifolds in the mash tun or copper wort chillers).[1] Even at low concentrations, dissolved copper is harmful to the brewing process, mainly because it significantly increases the rate of oxidation via Haber-Weiss reactions.[2] Iron can also directly impact flavor by contributing a metallic flavor(?)[citation needed]

Potential sources of copper[edit]

  • Grain - Depending on the malts used, a standard wort has levels of around 20–400 μg/L copper.[3] Copper extraction peaks within mash pH 5.5-5.7.[4]
  • Water - Copper is often present in tap water.[5] The level may be particularly high when copper piping is used.[6] Brewing liquor should contain < 0.1 mg copper/litre.[1]
  • Brewing equipment - Copper can be leached from any copper being equipment in contact with the brewing water, wort, or beer.
  • Another source of copper ions was the older, copper-based fungicides applied to hops.[1]

Copper binds with the coagulating proteins, precipitates and is removed with the hot break during lautering (45, 46).[3]

Cu has a great affinity to bind to proteins, thus precipitating during boiling and being removed to some part with the hot trub.[7]

Copper content is decreased to some extent during fermentation.[2]

Effects of copper[edit]

  • Increased oxidation - Copper ions are radicals that catalytically promote oxidation reactions, even at concentrations below 0.05 mg/L (50 ppb).[2][8][1][9] These reactions result in a variety of negative effects, including haze and the formation of aroma-active carbonyl compounds that directly cause beer staleness.[2][1][10] See Oxidation and Transition metals.
  • Impaired mash enzyme function - Copper decreases both alpha- and beta-amylase activity.[11][12]
  • Impaired fermentation - Copper ions are toxic and mutagenic to yeasts, which accumulate them and develop "yeast weakness".[1] Copper is an essential micronutrient for yeast at low concentrations, acting as a cofactor in redox pigments.[10] However, it is toxic to yeast above 10 mg/L and disrupts yeast cell plasma membrane integrity.[10]
  • Copper may reduce the concentration and flavor effects of sulfur compounds (such as H2S) in beer.[10] Cu ions were reported to affect the formation of volatile sulfur compounds, which usually have a relatively low taste threshold in beer and, therefore, can damage beer flavor when exceeding their individual threshold (44).[7]

Ways to minimize copper[edit]

  • Use tannin additives during mashing.
  • Avoid using any copper or brass equipment in contact with wort or beer. Stainless steel is the preferred metal.[1]
  • Use RO water instead of tap water.

See also[edit]

Potential Sources

References[edit]

  1. ↑ a b c d e f g Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
  2. ↑ 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.
  3. ↑ a b 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.
  4. ↑ 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.
  5. ↑ Karim K, Guha S, Beni R. Comparative Analysis of chemical, physical and biological contaminants in drinking water in various developed countries around the world. J Water Resour Prot. 2020;12(8):714–728.
  6. ↑ Copper in drinking water.
  7. ↑ a b 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.
  8. ↑ Irwin AJ, Barker RL, Pipasts P. The Role of Copper, Oxygen, and Polyphenols in Beer Flavor Instability. J Am Soc Brew Chem. 1991;49(3):140–149.
  9. ↑ Nardini M, Cirillo E, Natella F, Mencarelli D, Comisso A, Scaccini C. Detection of bound phenolic acids: prevention by ascorbic acid and ethylenediaminetetraacetic acid of degradation of phenolic acids during alkaline hydrolysis. Food Chem. 2002;79(1):119–124.
  10. ↑ a b c d Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.
  11. ↑ https://www.semanticscholar.org/paper/The-influence-of-microelements-selenium-and-copper-Anto%C5%86enko-D%C5%ABma/578fd3bf7d11e58ac290ac5576e339aa578b817f?p2df
  12. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0031942203004308
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