Updated: Apr 10, 2018
In Part I we looked at how Total Dissolved Solids (TDS) in water impact the taste of coffee. We also wanted to know how much the pH (acidity and alkalinity) affected taste and so selected 4 different mineral waters with similar TDS counts. Once again, I partnered up with water sommelier, Götz of MaiAqua, for the test.
Note – I am in no way affiliated with MaiAqua. The reason for this test was purely in the interest of coffee.
We used one, light roasted, Kenyan coffee so we could focus on the water. All water was boiled and poured at the same time as per Coffee Rambler’s cupping guide. The table below shows the water used, their TDS and pH (7 is neutral, 0 acid and 14 basic). These are the pre-boil values.
BIB (Bag in Box)
You might notice these waters are not ideal for brewing coffee. The choices were made for similar TDS readings and vast differences in pH. Note that the pH scale is not linear. Using this table (below) we can see that Voss is 63 times more acid than Iceland Spring and 7.9 times more than bottled MaiAqua. That is the same difference between bottled MaiAqua and Iceland Spring.
If you love mathematics and formulae you can see more here.
The Taste Results
The bottled MaiAqua made the most rounded, enjoyable brew. No surprise that this water is closest to the SCA’s ideal. As may be expected, Voss had the most intense acidity of the 4 but Iceland Spring had a surprising sharpness. Ultimately though, after 12 minutes the difference between the perceived acidity of the brews was not great, although noticeable. As the TDS values were still fairly different (and the mineral makeup of those solids), the test was imperfect.
A more positive result would be that the tasters could all pinpoint that the bottled MaiAqua produced the most balanced coffee. Flavour clarity was greatest with this water too.
Although the pH of the water had a noticeable difference, it was small. When we take into account Part I, differences in the TDS count have a greater effect on how the taste of coffee is perceived. What would have interfered with the results in this test was the small quantities of minerals in the water and how they drew out flavour from the beans’ molecules.
For example, it’s understood that magnesium extracts fruitier and more acidic flavours, whilst calcium extracts creamier flavours and gives greater body. Bicarbonates, like baking soda, act to dull acidity but too much is detrimental to the liveliness of coffee. This fantastic article by FiveSenses goes into more detail explaining this balance of impurities in water. They directly and individually test for how magnesium chloride, calcium chloride and sodium bicarbonate affect the taste of coffee with lab-made water.
Without any background in chemistry, this all may seem rather daunting. However, an answer to the specialty coffee water question has presented itself. Third Wave Water have developed mineral capsules to add to distilled water (water with no impurities, 0 or single digit TDS). They have created a balance of these minerals that when dissolved in water, give the ideal permanent and carbonate hardness needed for the most desirable extraction.
As we can see, water for coffee is very complex and there are many variables that influence extraction and flavour. In water alone factors include pH, permanent (calcium and magnesium) hardness, carbonate hardness, other minerals like sodium, potassium, chlorine and their molecular structure, positive ions for binding with the negatively charged ions in coffee molecules (where our metals help), water temperature and flow rate. Now add them to all the variables introduced from coffee’s production life through to brewing and drop your jaw.
For reference: Lemon 2, Coffee 5, Water 7, Avocado 9, Soap 12
What’s the pH of brewed coffee?
One more note that may be of interest. The acidity of brewed coffee is around pH 4.5 to 5.5, but closer to 5. I recently checked the acidity of 5 different coffees brewed with the same water at the same time. There were 2 medium-dark roasted espresso blends, 2 light roasted single origins (Ethiopia and El Salvador) and an old, medium roasted El Salvador. The three single origins read at 4.9 whilst the espresso blends read 5 and 5.1. The washed Ethiopian tasted the most acidic whilst the medium roasted El Salvador was on par with the espresso blends for perceived acidity.
Overall I feel pH has little influence in how we perceive acidity in coffee, and it is more to do with the molecules which influence alkalinity. Read this from GrindScience for further information about chlorides, sulphates and carbonates in water.