Brew Water Crafting
Sources: The Physics of Filter Coffee by Jonathan Gagné (2020)
Most tap water worldwide is unsuitable for specialty coffee brewing without modification — either too hard, too alkaline, or containing chlorine. Rather than relying on bottled water or partial dilution, baristas can build custom brew water from scratch by adding specific mineral salts to pure (distilled or reverse-osmosis) water. This gives precise, reproducible control over the two parameters that most affect extraction: total alkalinity and total hardness.
See Brew Water Quality for the underlying chemistry and why these parameters matter.
Target Parameters
| Parameter | Recommended Range | Notes |
|---|---|---|
| Total Alkalinity (HCO₃⁻) | 20–70 ppm as CaCO₃ | 40–50 ppm is the specialty coffee community norm; lower preserves more acidity |
| Total Hardness (Ca²⁺ + Mg²⁺) | 50–150 ppm as CaCO₃ | Provides extraction capacity; Ca favors body, Mg favors complexity |
| pH | ~7.0 | Will be set by the alkalinity component |
For reference: 1 ppm as CaCO₃ = 0.4 mg/L Ca²⁺, or 0.24 mg/L Mg²⁺, or 1.22 mg/L HCO₃⁻.
Most city tap water has total hardness of 100–300+ ppm as CaCO₃ and alkalinity in a similar range — far outside the specialty window. Hard water requires either dilution with RO/distilled water or starting from pure water and adding minerals.
Mineral Ingredients
Hardness (positive ions)
| Mineral | Provides | Notes |
|---|---|---|
| Calcium chloride (CaCl₂) | Ca²⁺ | Adds hardness; Cl⁻ anion is flavor-neutral at low concentrations |
| Magnesium sulfate (MgSO₄) | Mg²⁺ | Also called Epsom salt; adds hardness; SO₄²⁻ is flavor-neutral at low concentrations |
| Magnesium chloride (MgCl₂) | Mg²⁺ | Alternative to MgSO₄ without sulfate |
Anecdotal evidence: higher Ca²⁺ favors body and sweetness; some Mg²⁺ adds flavor complexity. A common approach is to use both CaCl₂ and MgSO₄ to obtain a mix of Ca and Mg hardness.
Alkalinity (negative buffer ions)
| Mineral | Provides | Notes |
|---|---|---|
| Sodium bicarbonate (NaHCO₃) | HCO₃⁻ (alkalinity) + Na⁺ | Baking soda; not baking powder |
| Potassium bicarbonate (KHCO₃) | HCO₃⁻ (alkalinity) + K⁺ | Preferred over NaHCO₃ by some — avoids sodium |
Use small amounts: 40–70 ppm alkalinity as CaCO₃ is the target, and excess alkalinity (from NaHCO₃ or KHCO₃) is the most damaging parameter for flavor.
Less Common Alternatives
- Calcium carbonate (CaCO₃): difficult to dissolve in pure water; impractical
- Calcium sulfate (CaSO₄): harder to source; adds both Ca and SO₄
- Calcium citrate: affects alkalinity via citrate anion; complex to work with
Example Recipes
These are starting points based on community-validated recipes. Adjust to taste, since roast level and coffee origin interact with water chemistry.
Gagné-style light roast V60 water (approximate):
- Start with RO or distilled water
- Add ~50 mg/L CaCl₂ (anhydrous) → ~35 ppm Ca hardness as CaCO₃
- Add ~40 mg/L MgSO₄ (anhydrous) → ~20 ppm Mg hardness as CaCO₃
- Add ~30 mg/L KHCO₃ → ~25 ppm alkalinity as CaCO₃
- Result: ~55 ppm hardness, ~25 ppm alkalinity — bright, clean
Standard specialty water (SCA range):
- ~100 ppm total hardness as CaCO₃ (mix of Ca and Mg)
- ~40–50 ppm total alkalinity as CaCO₃
- pH ~7.0
Soft water recipe (mimics lighter-roasted character):
- Lower total hardness (~40–60 ppm)
- Lower alkalinity (~20 ppm)
- Produces brighter acidity — good for washed light roasts
Measuring Water Parameters
Total Alkalinity (KH)
Options in order of increasing precision:
- API KH titration kit (aquarium test kit): affordable, adequate precision for most needs; extend precision by using a 20 mL sample instead of the standard 5 mL
- Back titration: add a fixed amount of acid reagent, then titrate back with base — requires less reagent, higher precision
- Hanna Instruments colorimeter (e.g. HI775): high precision, consistent regardless of water composition; the most reliable tool for lab-quality measurement
Total Hardness (GH)
Same method options as alkalinity. API GH titration kit works well with a stretched 20 mL sample. Colorimeter preferred for high-accuracy work.
Practical Note
Alkalinity and hardness titration kits sold for aquariums are inexpensive and widely available. Commercial kits labeled “carbonate hardness” actually measure total alkalinity (a common misnomer). Always verify which parameter a test kit is actually measuring before relying on it.
Consistency Tips
- If using a large batch of custom water in a bottle, shake well immediately before use — minerals can settle or stratify
- Avoid letting custom water sit in a hot kettle long enough to boil off significantly — heavy evaporation raises mineral concentrations
- Descale equipment periodically; even relatively soft custom water can deposit scale over time
- Seasonal drift in tap water composition can alter any dilution-based recipe — remeasure periodically
Relevance to Kaiserblick
Kaiserblick’s export markets in Germany, Belgium, Switzerland, Austria, France, and the Netherlands all have highly variable tap water. German cities range from very soft (Cologne, Hamburg) to moderately hard (Munich, Berlin). Swiss water is often moderately hard. Any customer using tap water without adjustment may be getting a systematically different expression of the coffee than intended by the roaster.
Providing simple water crafting guidance — or at least a recommendation to test local alkalinity — is a concrete service Kaiserblick can offer alongside green coffee and roasted coffee sales.