Water for Coffee Part I - A TDS taste test and the importance of water

Water makes up over 98% of brewed coffee and is the solvent for extracting flavour from the beans. As you might imagine, it is important to use the right water for brewing. But how much does water affect taste? How does it affect acidity, bitterness and flavour? I joined up with a water sommelier, Götz of MaiAqua, for a brew session.

Note – I am in no way affiliated with MaiAqua. The reason for this test was purely in the interest of coffee.

A number of factors can affect the taste of coffee in water. Obvious factors are temperature and volume. These variables were controlled by boiling water in 3 kettles simultaneously. Equal amounts of coffee and water were used in each cup. Total Dissolved Solids (TDS – all minerals dissolved in the water), water hardness (calcium and magnesium) and pH also play a part. For this test, we wanted to focus on the effects of TDS and hardness, with less focus on pH. It is generally considered water with a TDS reading of 80-250 milligrams per litre (mg/L) is best for coffee, 150 being the target.

3 types of water was used: Watson’s (distilled), MaiAqua and Evian. We chose 3 very different waters for more dramatic results and repeated the test twice for each coffee to take into account singular bean defects. Below is some more information about the water.

We also used 3 quite different coffees for the test, to see how water affected the final brew of different roasts. Information is below.

We cupped the coffees as per Coffee Rambler’s brew guide, with 11 grams of coffee to 200ml of water. Four of us tasted the different coffees with results marked below. Tasters were from UK, Germany, China and Brazil.

Results

The overall consensus was Watson’s distilled water made the coffee sour and flavourless. However, I enjoyed the bitter orange acidity of Tanzania.

MaiAqua was generally balanced, a little unexciting but matured well through the tasting. Acidity was dulled but sweetness was clear.

Evian was generally not so clean, flavour wise. The coffee also tasted dry and a little chalky/salty. The body was good and full though, particularly with the Sulawesi, which was described as satisfying.

Ultimately all 4 tasters had different favourites, the unfamiliar drinkers of light roasted, specialty coffee did not enjoy the distilled water. The waters enjoyed most were generally split between MaiAqua and Evian.

For all coffees the grounds behaved the same in the different waters; that is they sunk or floated depending on the water. Perhaps no surprise if we think about how people float more easily in the Dead Sea.

Conclusion

The type of water has a massive effect on the taste of coffee. The only water that fell into the advised TDS range, MaiAqua, performed best among the tasters for its balance, although a more lively acidity would have been appreciated. This may be achieved with water which has more magnesium. MaiAqua has only 4ml/L.

Watson’s distilled water tasted the sourest, but this might be because it was the most acidic of the waters. It also lacked flavour. With so many intense tastes, distilled water should be avoided when brewing coffee. It also lacks magnesium and calcium ions, needed to extract certain flavoursome compounds. However, it is important to note it performed well with the wet-hulled, darker-roasted coffee from Sulawesi.

When choosing bottled water for your coffee, look at the label to see if its contents fit the ideal ranges. If using tap water, measure the water with a TDS pen or filter it as many big cities have very hard water, not conducive to making good coffee or tea. Ultimately it’s best to experiment with water and discover what matches you best.

As a last note, remember that coffee’s solids are dissolved into water and the minerals within act as agents for extracting molecules. But even water with the same TDS will produce different tasting brews depending on the pH, hardness, sodium levels and other minerals. The amount of oxygen in the water plays a part too. This article does a great job at explaining this more scientifically but be aware that the enjoyment of coffee’s taste is also subjective.

If you’re feeling brave you can also make your own water. Matt Perger has a recipe he feels best favours filter coffee.

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