Why Each Mineral Matters Differently
| Mineral | Optimal range (mg/L) | Too low effect | Too high effect | Key interaction |
|---|---|---|---|---|
| Calcium (Ca²⁺) | 10–50 mg/L | Very flat, no body | Polyphenol scum, dull, alkaline | Binds polyphenols and theaflavins |
| Magnesium (Mg²⁺) | 5–15 mg/L | Thin, watery | Bitter, coarse | Enhances catechin extraction |
| Bicarbonate (HCO₃⁻) | 10–50 mg/L | More acidic, sharper | Raises pH, dulls colour, flat | pH buffer — controls brew acidity |
| Sodium (Na⁺) | 5–15 mg/L | Slightly flat | Salty (above 30+) | Potentiates umami receptors |
| Potassium (K⁺) | 1–10 mg/L | No strong effect | Very uncommon problem | Minor umami enhancement |
| Sulfate (SO₄²⁻) | 10–30 mg/L | No strong effect | Dry, mineralised | Slightly enhances bitterness profile |
| Chloride (Cl⁻) | 10–30 mg/L | Flatter taste | Salty, medicinal | Accentuates sweetness and body |
Category-Specific Recommendations
Delicate green and white teas (gyokuro, matcha, Silver Needle): aim for TDS 50–100mg/L, calcium <30mg/L, magnesium 5–10mg/L, bicarbonate <30mg/L. Reverse osmosis water with a small addition of Epsom salt (MgSO₄) achieves an ideal profile.
First-flush Darjeeling and high-grown oolongs: TDS 80–130mg/L, calcium 20–40mg/L, magnesium 8–15mg/L. Slightly harder water than for delicate greens supports the more robust polyphenol extraction.
Black tea for brewing with milk: tolerates TDS 100–200mg/L; the milk proteins buffer the polyphenol-calcium interaction. Very hard water still reduces polyphenol extraction even with milk.
🧠 Expert Tip: DIY Water Recipe
Start with reverse osmosis or deionised water (pure). Add: 50mg/L calcium bicarbonate (source: food-grade calcium bicarbonate powder, available from homebrew shops) + 15mg/L magnesium sulfate (Epsom salt) + 5mg/L sodium chloride. This produces TDS approximately 90mg/L with a balanced mineral profile suitable for most quality teas, at nearly zero cost.
Testing Your Current Water
An inexpensive TDS meter (£10–20) gives you an instant reading of total mineral content. Your local water company publishes detailed mineral analyses online (usually under "water quality" or "annual report"). For full detail, inexpensive water test kits (Salifert, Hanna instruments) measure individual ions. Once you know what you have, you can decide what to remove (via filtration) and what to add (via mineral supplementation).
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