The Role of Water
Part 1 : Shallow dive into the water for speciality coffee
One of the aspects I admire most about the specialty coffee community is its drive to nurture curiosity and explore endless possibilities in the world of coffee. In specialty coffee, we honour the hard work and expertise farmers put into cultivating great beans for us to roast, but do we realise that to fully respect the bean, we also need to ensure the quality of the water? Just like the famous line, “Water, water everywhere, and not a drop to drink” in Coleridge’s poem, ‘The Rime of the Ancient Mariner,’ water is everywhere, but not all is good enough to use for coffee!
Water comprises 98% of our cup of coffee, and it’s not just the H₂O molecule. It’s a complex solution of minerals, acids, and compounds that significantly affect the flavour and quality of our coffee. With this in mind, we would like to take you on a shallow dive into the importance of water quality in brewing your delicious cup of coffee. While this is only a shallow dive, I’ll suggest where to find resources for a deeper dive at the end.
SCA Water Control Chart: Illustrates the ideal range for hardness and alkalinity.
What’s in Water, and Why Does It Matter?
Two key guidelines must be followed to optimise the quality of water for coffee brewing:
● To enhance flavour, achieve the right balance of minerals to bring out the best characteristics of the coffee.
Measuring the Quality of Your Brewing Water:
Let’s start with manual brewing methods like the V60 pour-over, before delving into water quality for espresso. First, take a water sample —whether tap or RO (Reverse Osmosis)— taste and smell it. It should be odourless and tasteless. Next, measure the Total Dissolved Solids (TDS) in parts per million (PPM), which reflects the combined content of dissolved minerals like calcium, magnesium, and trace metals.
The Specialty Coffee Association (SCA) recommends a TDS of 75-150 PPM for brewing coffee, but TDS alone doesn’t tell us how much calcium and magnesium is present. That’s why we test for both hardness and alkalinity, two important parameters to perfect your brew.
How to test for Alkalinity and Hardness:
Alkalinity is measured by titrating with an acid (often sulfuric acid) until the water’s pH reaches about 4.5, indicating neutralisation of bicarbonates, carbonates, and hydroxides. The amount of acid required gives us the sample’s alkalinity.
Hardness is measured by titrating with EDTA (ethylenediaminetetraacetic acid), a chemical that binds strongly to calcium (Ca²⁺), magnesium (Mg²⁺) and other metal ions. In this process, a known amount of water sample is placed in a container, and a colour indicator is added. EDTA solution is then slowly added to the sample. As EDTA binds to the metal ions, it removes them from solution. When all the calcium and magnesium ions are bound, the colour of the solution changes (see in our photo below), signalling the endpoint of the titration. The amount of EDTA needed to reach this endpoint directly corresponds to the total hardness of the water sample, reflecting the concentration of these metal ions.
A pH test will also indicate water’s acidity or alkalinity. Ideally, for coffee, the pH should be close to 7, ranging between 6.5 and 7.5. Water that’s too alkaline or acidic can negatively impact extraction and flavour.
The Balance of Calcium and Magnesium:
Studies show that excessive calcium carbonate in water buffers coffee’s natural acidity, leading to a flat taste. Conversely, magnesium helps bring out floral and bright notes. For pour-over brewing, the optimal concentration of these minerals tends to fall between 40-70 mg/L, but this can vary based on the coffee varietal and brew method.
