tags: [] - coffee/brewing - coffee/brewing/water aliases: - Magnesium sulfate coffee - MgSO4 coffee water - Epsom salt water recipe

Epsom Salt¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Magnesium sulfate coffee, MgSO4 coffee water, Epsom salt water recipe Related: Water in Coffee MOC | Magnesium in Coffee Water | DIY Water Recipes | Magnesium vs. Calcium | Sulfate in Coffee Water Status: ✅ Complete

Overview¶

Epsom salt (magnesium sulfate heptahydrate, MgSO₄·7H₂O) is the most commonly used mineral ingredient in DIY coffee water recipes, providing magnesium (Mg²⁺) and sulfate (SO₄²⁻) ions to distilled or reverse osmosis water. Magnesium is the preferred hardness ion for specialty coffee water because it extracts organic acids and aromatic compounds more effectively than calcium. Epsom salt is widely available in pharmacies and supermarkets, is food-safe, highly soluble, and inexpensive — making it the standard magnesium source in barista and enthusiast water recipes worldwide.

Chemical Properties¶

Common name: Epsom salt (named after Epsom, Surrey, UK)
Chemical name: Magnesium sulfate heptahydrate
Formula: MgSO₄·7H₂O
Molecular weight: 246.5 g/mol
Magnesium content: 9.86% Mg by mass → 1 g/L solution provides ~98.6 mg/L Mg²⁺
Sulfate content: 38.97% SO₄ by mass → 1 g/L solution provides ~389.7 mg/L SO₄²⁻
Solubility: ~71 g/100 mL at 20°C; highly soluble; dissolves readily in water

Because Epsom salt is ~10% Mg by mass and the amount needed for coffee water is very small (typically 0.02–0.05 g/L to achieve 2–5 mg/L Mg²⁺ in a simple recipe, or working from a 10× stock), precise measurement is important.

Effect on Coffee¶

Magnesium (Mg²⁺): - Enhances extraction of organic acids and aromatic compounds (Hendon et al. 2014) - Produces brighter, more complex, more aromatic cups - Preferred over calcium as the primary hardness source in filter coffee water

Sulfate (SO₄²⁻): - At low concentrations (<100 mg/L): contributes dry body, minerality, and slight bitterness enhancement - At moderate concentrations (100–200 mg/L): increasingly noticeable dry or harsh note - At high concentrations (>300 mg/L): can be objectionable; produces harsh, sulfurous, or mineralised character

For filter coffee recipes, Epsom salt use should be calibrated to achieve the magnesium target while keeping sulfate within acceptable range. If magnesium is desired with less sulfate, magnesium bicarbonate (prepared concentrate) is an alternative.

Typical Use in Water Recipes¶

Two-ingredient recipe (Epsom salt + potassium bicarbonate, per litre of distilled water): - Epsom salt: 0.3–0.5 g/L → ~30–50 mg/L Mg²⁺, ~120–195 mg/L SO₄²⁻ - Potassium bicarbonate: 0.15–0.25 g/L → ~40–70 mg/L HCO₃⁻ (~33–57 mg/L as CaCO₃)

Stock solution method: - Prepare 10 g/L Epsom salt in distilled water (10× concentrate) - Add 1 mL of stock per litre of water → ~0.985 mg/L Mg²⁺ (adjust volume to target) - Allows syringe-precision dosing for recipe consistency

Sourcing and Purity¶

Food-grade or pharmaceutical-grade Epsom salt is the appropriate grade for coffee water. Epsom salt sold for bathing or gardening is typically also magnesium sulfate but may contain additives in scented products — plain, unscented Epsom salt should be used. Available from pharmacies, supermarkets, and online suppliers.

Key Facts¶

Epsom salt (MgSO₄·7H₂O): 9.86% Mg, 38.97% SO₄; 1 g/L provides ~99 mg/L Mg²⁺
Standard magnesium source for DIY coffee water recipes; highly soluble and widely available
Magnesium improves extraction efficiency and cup brightness (Hendon et al. 2014)
Simultaneously contributes sulfate — use within recipe limits to avoid harsh, dry, mineralised character
Use plain, unscented food-grade or pharmaceutical-grade Epsom salt; work from stock solutions for precision

References¶

Changelog¶

Date	Change
2026-04-28	Note created
2026-05-02	Compliance review: added --- before copyright

This article is part of All-About-Coffee.com - The comprehensive coffee knowledgebase.