Fault
Metallic
A coin-like metallic note, usually from corroded equipment or high-iron brewing water.
Also called tinny, coin, blood.
What it tastes and smells like
Responsible compound: iron and other metal ions.
If you are drinking it
A metallic taste is a brewing fault rather than anything to do with a can — the modern can liner does not contribute metal flavour. It is harmless.
Not a safety issue. Beer’s alcohol, hop compounds and low pH make it inhospitable to organisms that cause illness.
What causes it
| Cause | Stage | How often | Who can act |
|---|---|---|---|
| Rust or scale on kettles, chillers or fittings dissolving into hot wort. | boiling | most common | brewer |
| Brewing water with elevated iron content, which is also implicated in accelerated staling. | raw materials | common | brewer |
| Oxidation of grain lipids, particularly where milled grain has been stored badly, can read as metallic. | mashing | occasional | brewer |
If you are brewing it
- Brewer: Replace corroded fittings, use stainless steel throughout, and avoid abrasive cleaning that removes the passive layer. (prevents)
- Brewer: Filter or treat brewing water, or blend with reverse-osmosis water to dilute the iron. (prevents)
Where in the process this comes from
Steps that can produce this fault when they go wrong. Each links to what the step is for and how it is controlled.
- Water treatment — Adjust the mineral content and alkalinity of brewing water so the mash reaches a workable pH and the finished beer has the intended balance.
Evidence
What BeerHQ knows about this, and how. Every statement carries the state of the evidence behind it rather than being presented flatly as fact.
Iron in finished beer sits at the fraction-of-a-milligram-per-litre scale: one survey of thirteen craft beers found 0.125–0.316 mg/L, with five of the thirteen above the 0.2 mg/L limit those beers were regulated against.
Checked against the source
Source: López-Balladares et al., "Electrochemical Evaluation of Cd, Cu, and Fe in Different Brands of Craft Beers from Quito, Ecuador" (2023), results, Table of Fe and Cu (Foods 12(11):2264)
Iron reaches beer from more than one direction — the barley itself, process additives, and corrosion of brewing equipment — and darker malts are associated with more of it, since hot water extracts metal more readily from roasted grain.
Checked against the source
Source: López-Balladares et al., "Electrochemical Evaluation of Cd, Cu, and Fe in Different Brands of Craft Beers from Quito, Ecuador" (2023), results and discussion (Foods 12(11):2264)
Iron and copper in beer do damage beyond any taste of their own: they induce molecular oxygen to form reactive oxygen species, which participate in oxidising the beer and produce unpleasant flavours.
Checked against the source
Source: Martínez-Gómez et al., "Phenols and Melanoidins as Natural Antioxidants in Beer" (2020), section 5, antioxidant measurement (Biomolecules 10(3):400)