Copper
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In 1934, Haber and Weiss found final proof for the formation of radicals in aqueous solutions of bivalent copper ions together with hydrogen peroxide (now called Haber-Weiss reactions) and described the strongly oxidative character of these radicals. Copper ions are known to have a negative influence on beer flavor stability. Even concentrations of copper below 50 ppb are reported to cause damage in the final product. The origin copper in beer from raw materials, brewing equipment, diatomaceous earth etc. has been well investigated.[1]
The Haber-Weiss reaction consists of a Fenton reaction coupled with a reaction between oxidized metal ion and superoxide, the superoxide thus serving to recycle the metal through its Fenton-active, reduced state.[2]
Copper content is decreased to some extent during fermentation.[1]
The rate of flavor staling in beer is significantly increased by traces of Cu(II), even at levels below 100 mcg/L (100 ppb). The Cu(II) catalyzes oxidation reactions that require pro-oxidants such as cysteine and 1,2,3-trihydroxypolyphenols to recycle the copper through its reduced state. Primary alcohols can be coupled to the oxidation process to yield aldehydes among the products.[2] Because oxygen is a triplet species, it is fundamentally slow to react with organic compounds in their singlet ground states. Consequently, transition metal ions in beer have been proposed as catalysts that activate molecular oxygen.[2]
One study: batches of production lager were taken over a four-month period, analyzed for copper and iron, and stored at 23° C for five months. The same taste panel then scored the stale flavor intensity of each batch. An obvious correlation was found to exist between the stale flavor intensity and the copper ion concentration, which varied from 40 to 95 mcg/L[2]
Copper (Cu2+, at. wt. 63.5) presented problems in brewing when vessels and pipework were made of copper but since these have come to be made of stainless steel there have been fewer problems with dissolved copper in breweries. Copper ions are toxic and mutagenic to yeasts, which accumulate them and develop "yeast weakness". Another source of copper ions was the older, copper-based fungicides applied to hops. Copper ions are oxidation/reduction catalysts and their presence favours flavour instability and haze formation in beer. Brewing liquor should contain < 0.1 mg copper/litre.[3]
Copper is an essential micronutrient for yeast at low concentrations, acting as a cofactor in redox pigments.23 However, it is toxic to yeast above 10 mg/L2,18 and disrupts yeast cell plasma membrane integrity.23 It can contribute to haze formation2 and may reduce the concentration and flavor effects of sulfur compounds (H2S) in beer.5 Also, copper ions have a negative effect on beer flavor stability.23[4]
Copper had been shown to decrease both alpha- and beta-amylase activity.[5][6]
cupric ions have been reported to catalyse the oxidation of caffeic acid at neutral pH (Nardini et al., 1995).[7]
Depending on the malts used, a standard wort has levels of around 20-400 μg/L copper.[8]
copper is often present in tap water.[9]
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).[10]
Cu was reported to have a great affinity to bind to proteins, thus precipitating during boiling and being removed to some part with the hot trub (14,52).[10]
Potential Sources
- https://www.apps.fst.vt.edu/extension/enology/downloads/SLOFactorsFinal.pdf
- https://onlinelibrary.wiley.com/doi/abs/10.1111/ajgw.12159
References[edit]
- ↑ a b Zufall, C., and Tyrell, Th. "The Influence of Heavy Metal Ions on Beer Flavour Stability." J. Inst. Brew., vol. 114, no. 2, 2008, pp. 134–142.
- ↑ a b c d 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.
- ↑ Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
- ↑ Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.
- ↑ https://www.semanticscholar.org/paper/The-influence-of-microelements-selenium-and-copper-Anto%C5%86enko-D%C5%ABma/578fd3bf7d11e58ac290ac5576e339aa578b817f?p2df
- ↑ https://www.sciencedirect.com/science/article/abs/pii/S0031942203004308
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ 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.