tags: [] - coffee/brewing - coffee/brewing/water aliases: - Magnesium versus calcium coffee - Ca vs Mg coffee water - Calcium magnesium comparison

Magnesium vs. Calcium¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Magnesium versus calcium coffee, Ca vs Mg coffee water, Calcium magnesium comparison Related: Water in Coffee MOC | Magnesium in Coffee Water | Calcium in Coffee Water | Hardness | Magnesium and Brightness Status: ✅ Complete

Overview¶

Magnesium (Mg²⁺) and calcium (Ca²⁺) are the two hardness-contributing cations in coffee brewing water, and while both contribute to total hardness and body, they differ significantly in their extraction efficiency and flavour impact. The key research finding from Hendon et al. (2014) is that magnesium extracts coffee flavour compounds — particularly organic acids and aromatic molecules — more effectively than calcium at equivalent molar concentration. This difference has driven the adoption of magnesium-forward water recipes in specialty coffee, where magnesium is preferred as the primary hardness source.

Comparison Table¶

Property	Magnesium (Mg²⁺)	Calcium (Ca²⁺)
Extraction efficiency	Higher — extracts more organic acids and aromatics	Lower at equivalent concentration
Cup character	Brighter, more aromatic, higher perceived acidity	Rounder body; less brightness per unit hardness
Crema contribution	Less specific	Contributes to crema stability in espresso
Scale risk	Lower — MgCO₃ forms more slowly and is softer	Higher — CaCO₃ forms readily and is hard/adherent
SCA water recipe preference	Preferred primary hardness source	Secondary; used for balance and crema
DIY recipe ingredient	Epsom salt (MgSO₄·7H₂O) or Mg(HCO₃)₂	Calcium chloride (CaCl₂) or chalk
Molar mass	24.3 g/mol	40.1 g/mol

Why Magnesium Extracts Better¶

The higher extraction efficiency of magnesium is attributed to differences in ionic charge density and binding affinity: - Mg²⁺ has a smaller ionic radius (72 pm) than Ca²⁺ (100 pm) for the same 2+ charge, giving it higher charge density - Higher charge density = stronger electrostatic interaction with polar functional groups on coffee solubles (carboxylate groups of organic acids, carbonyl groups of aromatic compounds) - This stronger interaction effectively draws more of these compounds into solution during brewing

Practical Implications for Water Recipe Design¶

Specialty coffee water recipes — including the Barista Hustle recipe (Colonna-Dashwood & Scott Rao) and Third Wave Water — use magnesium as the primary hardness contributor, typically providing: - 20–30 mg/L Mg²⁺ for filter coffee (as elemental magnesium) - Some calcium for balance and crema stability (particularly for espresso recipes)

A typical light roast filter recipe might target: - ~25 mg/L Mg²⁺ from MgSO₄ (Epsom salt) - ~10 mg/L Ca²⁺ from CaCl₂ - ~30–40 mg/L alkalinity from magnesium bicarbonate or potassium bicarbonate

A typical espresso recipe might target: - ~20 mg/L Mg²⁺ - ~20–30 mg/L Ca²⁺ (for crema) - ~40 mg/L alkalinity

Scale Considerations¶

At equivalent concentration, calcium forms harder, more adherent scale than magnesium: - CaCO₃ (calcite) is relatively insoluble and adheres strongly to metal surfaces - MgCO₃ (magnesite) is somewhat more soluble and forms softer deposits - Using magnesium-dominant water moderately reduces scale accumulation rate in boilers and group heads

Key Facts¶

Magnesium extracts coffee flavour compounds more effectively than calcium at equivalent concentration (Hendon et al. 2014)
Magnesium-dominant water produces brighter, more aromatic, more complex cups; calcium-dominant water produces rounder body with less brightness
Calcium contributes more specifically to espresso crema stability
Magnesium forms less problematic scale than calcium (MgCO₃ vs. CaCO₃)
Specialty water recipes use Epsom salt (MgSO₄) for magnesium, calcium chloride for calcium

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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