Make Your Own Brew Water for Coffee Using Mineral Concentrates. (Practical Edition)

Abstract

This guide presents a practical method for preparing mineral concentrates intended for precision water design in coffee brewing. By empirically determining a mineral's conductivity contribution (K-factor) using a 442-calibrated TDS meter, custom concentrates can be prepared to achieve controlled ppm increases with high accuracy. This method enables users to create stock solutions (e.g., 5 ppm or 10 ppm increases per mL) with minimal error, enhancing brew water reproducibility.

Introduction

Water composition significantly affects coffee extraction and flavour. Accurate remineralisation using precise concentrates allows for customised water profiles tailored to brewing needs. Traditional methods rely on theoretical ionic mass calculations; however, real-world conductivity measurements offer a more accurate basis for practical concentrate preparation. This guide describes a method to determine a mineral’s empirical conductivity contribution and use it to formulate precise mineral concentrates.

Materials

• Magnesium Chloride Hexahydrate (MgCl₂·6H₂O)
• Calcium Chloride Dihydrate (CaCl₂·2H₂O)
• Potassium bicarbonate (KHCO₃)
• Sodium bicarbonate (NaHCO₃)
• Scientific Laboratory Pipette
• 250 mL bottle per mineral concentrate
• Distilled / Reverse Osmosis 0 ppm Water
• Scale (±0.01 g accuracy)
• TDS Meter - 442-calibrated
  

Key Concept: The K-Factor

K = how many ppm your salt produces per 1 g/L of solution, measured using a 442-calibrated TDS meter.

Every mineral has its own K-factor based on how it behaves in real water. Repeat Step 1 below for every salt to determine its specific value. Do not assume K is the same across minerals.

In this example we used MgCl₂·6H₂O.

Step 1: Find Your Mineral’s K-Factor

1. Make a 2 g/L solution:

Dissolve 1.0 g of your mineral in 500 mL of 0 ppm water

Concentration = 1.0g / 0.5L = 2.0g/L

2. Measure TDS with your 442-calibrated meter

Example TDS reads 1500 ppm

3. Calculate K:

K = TDS reading (ppm) / Solution concentration (g/L)

Example:

K = 1500 ppm / 2.0 g/L = 743.8 ppm per g/L

What This Means:

1.0 g/L of your mineral ~ 743.8 ppm TDS on your meter.

2.0 g/L of your mineral ~ 1487.6 ppm TDS (as measured).

You will need to Repeat Step 1 for each salt to determine its unique K-factor. Always validate for each salt.

Step 2:Calculate How Much Mineral You Need For The Concentrate

For a 10 ppm TDS increase:

Dilution factor: 1 mL into 500 mL = ×500

Required TDS in concentrate: 

Concentrate TDS = 10 ppm × 500 = 5000 ppm.

Mass needed (for 500 mL concentrate):
Mass(g) = (Concentrate TDS / K ) x Volume (L)

Example:
(5000 ppm / 743.8) x 0.5 = 3.36 g

For a 5 ppm TDS increase:

Dilution factor: 1 mL into 500 mL = ×500

Required TDS in concentrate: 

Concentrate TDS = 5 ppm × 500 = 2500 ppm.

Mass needed (for 500 mL concentrate):
Mass(g) = (Concentrate TDS / K ) x Volume (L)

Example:
(2500 ppm / 743.8) x 0.5 = 1.68 g

Step 3: Prepare Your Concentrate

For 10 ppm: Dissolve 3.36 g of mineral (in this case MgCl₂·6H₂O) into 500 mL of distilled/RO water.

For 5 ppm: Dissolve 1.678 g of mineral (in this case MgCl₂·6H₂O ) into 500 mL of distilled/RO water.

Mix thoroughly until fully dissolved.

Step 4: Validate Your Solution

Add 1 mL of the concentrate to 500 mL of 0 ppm water.Measure TDS:

Note: K assumes linear conductivity. For even greater accuracy, verify your K-factor with additional calibration points (e.g., 5 g/L and 10 g/L solutions).

Expected Results:

For 10 ppm concentrate → TDS should read ~10 ppm.

For 5 ppm concentrate → TDS should read ~5 ppm.

If your readings are slightly off:

If TDS is lower: Increase the mineral mass slightly (e.g., in this case from 3.36 g to 3.5 g).

If TDS is higher: Reduce the mineral mass slightly (e.g., in this case from 3.36 g to 3.1 g).

Key Takeaways

The K-factor is specific to each salt and your meter setup.

Once you know K, you can easily create any strength concentrate.

Always validate by testing a few drops into 0 ppm water.

K-values are based on empirical testing with COM-100 TDS meter. Your values may vary slightly due to meter calibration or salt purity.

Always repeat Step 1 for each mineral to determine its unique K-factor.