tags: [] - coffee/brewing - coffee/brewing/water aliases: - Magnesium coffee water - Mg2+ coffee - Magnesium ion coffee

Magnesium in Coffee Water¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Magnesium coffee water, Mg2+ coffee, Magnesium ion coffee Related: Water in Coffee MOC | Hardness | Calcium in Coffee Water | Magnesium and Brightness | Magnesium vs. Calcium Status: ✅ Complete

Overview¶

Magnesium (Mg²⁺) is the hardness-contributing cation that most effectively extracts flavour compounds from coffee grounds — more effective than calcium at equivalent concentration. Research by Hendon et al. (2014) demonstrated that magnesium preferentially extracts organic acids and aromatic volatile compounds, producing brighter, more complex, and more aromatic cups compared to calcium-dominant water at the same total hardness. For this reason, water recipes for specialty coffee favour magnesium as the primary hardness source, often provided as magnesium bicarbonate or magnesium sulfate (Epsom salt) in DIY mineral water recipes.

The Hendon Finding¶

The 2014 study by Hendon et al. at the University of Bath directly compared the extraction performance of calcium and magnesium ions. Key findings: - Magnesium extracted more total solubles from coffee than calcium at equal molar concentrations - The compounds preferentially extracted by magnesium include organic acids (citric, malic) and aromatic molecules that contribute brightness, fruit character, and complexity - Calcium extracted somewhat different profiles and was less effective overall - The mechanism is attributed to differential binding affinities of Ca²⁺ vs. Mg²⁺ for the functional groups on coffee's organic molecules

This finding has been widely adopted in specialty coffee water recipe design, where magnesium is the preferred cation for achieving extraction quality.

Magnesium and Cup Character¶

In practical brewing terms, magnesium-dominant water (relative to calcium, at equivalent hardness): - Produces brighter, more acid-forward cups - Enhances fruit character and aromatic complexity - Supports clarity and transparency of flavour - May increase perceived sweetness by emphasising complementary organic acid character

Magnesium and Scale¶

Magnesium can form magnesium carbonate scale (MgCO₃) when heated in bicarbonate-rich water, but: - Magnesium carbonate scale forms more slowly than calcium carbonate at equivalent concentrations - Magnesium carbonate scale is softer and more soluble than calcium carbonate, making it easier to remove with descaling agents - In practice, scale in coffee equipment is predominantly calcium carbonate; magnesium scale is a secondary concern

Magnesium in Water Recipes¶

Magnesium is typically added to DIY coffee water recipes as: - Magnesium sulfate (MgSO₄ · 7H₂O — Epsom salt): Widely available and inexpensive; contributes Mg²⁺ and SO₄²⁻; sulfate adds some dryness and body - Magnesium bicarbonate (Mg(HCO₃)₂): Contributes Mg²⁺ and HCO₃⁻; the bicarbonate also provides mild alkalinity — useful for balancing recipes; prepared by pressurising water with CO₂ in the presence of magnesium hydroxide powder

Popular water recipes for coffee (Barista Hustle recipe, Third Wave Water) include magnesium as the primary hardness contributor.

Key Facts¶

Magnesium extracts coffee flavour compounds (especially organic acids and aromatics) more effectively than calcium (Hendon et al. 2014)
Magnesium-dominant water produces brighter, more complex, more aromatic cups than equivalent calcium-dominant water
Forms less problematic scale than calcium; MgCO₃ is softer and more soluble than CaCO₃
Added in DIY recipes as Epsom salt (MgSO₄ · 7H₂O) or magnesium bicarbonate
SCA hardness target (68 mg/L as CaCO₃ total) encompasses both Ca²⁺ + Mg²⁺; specialty recipes favour Mg as primary source

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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