At La Cabra this is exactly how we see water. Finding the right water is of the highest importance when chasing exciting coffee experiences. Water makes up more than 98% of a black brew, and around 90% of an espresso, so the water chosen makes a huge difference to all aspects of the final character of the brew. Not only this, but the balance and level of the water’s mineral content makes a huge difference to what we are able to extract from coffee.
Dissolved minerals in water exist as charged ions, which help us to bind to the flavour compounds in coffee that lead to the most exciting and involving cups. For coffee brewing, we can think of these minerals existing in two broad categories, General Hardness (GH) and Carbonate Hardness (KH). For natural water hardness, the two most important GH ions are Magnesium and Calcium. Magnesium has a very strong attraction to natural acid molecules, so has a huge effect on perceived acidity in coffee, pulling out flavours we like to describe as fruits in coffee, normally sharper acidities like citrus and forest berries. Calcium has a slightly weaker interaction, so tends to enhance softer acidities like strawberry and cherry, while also directly enhancing body. The final piece in the puzzle is KH, which has a slightly more complicated interaction. Through a phenomenon known as buffering, the carbonate hardness tries to keep the pH (the scientific measurement of acidity) of the water around 7, which is neutral. This means that controlling KH is very important. Too little, and the coffee tastes unbalanced and sharply acidic, no matter what brewing parameters are changed. Too much, and it is impossible to perceive any acidity in the coffee, leaving a flat and dull cup.
There are several ways we can control this in our coffee brewing. Here at La Cabra, we use Everpure’s Reverse Osmosis systems to control the mineral content in our brewing water at both of our coffee bars in Aarhus. These systems allow us fine control over the Parts per Million (ppm, equivalent to milligrams per litre, or mg/L) of minerals present in our water, by softening our very hard source water, and mixing a controllable amount of source water back into the softened water, to create our brewing water. This means these systems are excellent solutions for cafes in hard water areas like Aarhus, but are designed for very high volume, so are very large and expensive for home use. For home users, whether in very soft or very hard water areas, there are two ways to improve the mineral content, use bottled water, or make custom water from scratch. For bottled water, we look for the highest possible Magnesium content you can find, as most bottled water has a very low level. For Calcium we look for a content of around 20 mg/L, and for Bicarbonate, try to keep below 50 mg/L, as most bottled waters have very high Bicarbonate content. In the UK and Ireland, Tesco sells a mineral water called Ashbeck which is perfect for all of these specifications. For making custom mineral content water, a source of distilled water is needed, which is normally available from pharmacies. Epsom bath salts are a source of Magnesium Chloride, and baking soda is a source of Sodium Bicarbonate.
It can be very exciting to experiment with different levels of these minerals and see how they affect coffee flavour.
There are great guides and recommended mineral contents on the links below.