There must be something in the water – the secret to the perfect cup of coffee

– Guest post from BWT Water 

The ratio of minerals in the water determines the extraction process and the taste of the coffee

The right ratio of magnesium to calcium is critical to get the best from every coffee and to fully develop the taste experience that coffee-roasters are looking to achieve. That is the key finding from a new study by the University of Applied Sciences in Zurich.

Coffee connoisseurs have long suspected that certain constituent elements in the water affect the taste of the coffee made using it, and baristas have puzzled over the fact that the high quality of their raw and roasted ingredients is not reflected in the taste experience in the cup. One intrepid group of scientists made it their mission to find out why…

A research team working under Prof. Chacan Yeretzian, with assistance from Dr. Marco Wellinger and Dr. Samo Smrke, used a standardised procedure to investigate the influence that the ratio of the minerals calcium (Ca2+) and magnesium (Mg2+) dissolved in the water had on the sensory properties of coffee.

It’s fair to say that water is the basis of coffee, so the effect that water quality actually has on the result in the coffee cup, should be a solid consideration. Under the guidance of Prof. Chahan Yeretzian, the Chair of the Research Advisory Council at SCAE (Speciality Coffee Association of Europe), the team carried out a study on the SCAE Water Chart. The aim was to quantify precisely the effect of water quality on the brew (i.e. a brewed coffee), from a sensory perspective.

The analysis focussed on the effect of the ratio of the alkaline earth metal ions Ca2+ and Mg2+ dissolved in the water on the sensory properties of coffee. In this statistically assured cupping panel (triplicate panel), coffees were sampled that had been prepared with three types of water with different compositions. Production of the brews was undertaken under constant conditions: the same variety of coffee with identical roasting and grinding, the same quantity of coffee, brewing temperature and extraction period. The only variable here was the water. Three types of water were used in the tests, and the alkalinity and overall hardness of all three were identical. Only the ratio of the calcium concentration to the magnesium concentration was varied in the water used to extract the brews. Accordingly, one water was provided with a high proportion of calcium (3:1), a second with equal proportions of calcium and magnesium (1:1), and a third with a low proportion of calcium (1:3) where the water was primarily mineralised with magnesium.

In each case, the respective sensory impression was assessed using the six sensations of taste and aroma: body, acidity, fruitiness, sweetness, bitterness and astringency.

A surprisingly clear picture

The taste analysis revealed a surprisingly clear picture: where the mineral content of the water shifted in favour of magnesium (Ca2+/Mg2+ = 1:3), this produced a very balanced, rounded taste profile in the coffee.
Astringency and bitterness were avoided. Acidity and sweetness remained constant, and fruitiness was maintained.
The research findings demonstrate that whether a coffee is able to develop its full aroma, and whether it tastes pleasant or not, depends to a large degree on the mineral composition of the water with which it was prepared.
If this balance is shifted in favour of magnesium, two key taste parameters change in the coffee extract: bitterness and astringency fall off significantly. In the Zurich study, the mix of calcium to magnesium in a ratio of Ca2+/Mg2+ = 1:3 proved to be the most suitable for  achieving a fine, richly-varied taste in which all the various nuances of the coffee can be appreciated, whilst at the same time effectively avoiding bitterness and astringency.

The academic finding is a very good match to the empirical experience of the baristas, that magnesium-rich water delivers a harmonious, rounded taste experience from the coffee.

With over 25 years of experience, BWT UK Limited is leading the UK in water treatment technology, supplying safe, high quality water to domestic, business and commercial & industrial environments. We’re proud to be the official water sponsor of Winchester Coffee Festival on September the 29th, making sure every cup you have on the day is perfect!


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