We discovered that like many things in life it is a trade-off between the two objectives, i.e. the kind of water you need for great coffee is at odds with the kind you need to ensure no limescale forms in your espresso machine.
Using a water with the lowest 'dry residue' value (expressed in mg/L) you can find will indeed ensure you never see scale in your machine, but unfortunately it will also make your coffee taste overly 'bright' and 'harsh'.
It is complicated by the fact that the bottled waters on the market tend to fall into one of two extremes; mineral waters with very high TDS values, and typically very hard, and the 'arctic' waters with very low TDS values, very low alkalinity and typically a pH of less than 7 (i.e. acidic).
The key parameters and their target values are:
pH = 7.0
Total dissolved solids(TDS), often stated as 'dry residue@180C' = 120-130 mg/L
Hardness = 70-80 mg/L
Alkalinity = 50mg/L
You will soon find yourself saying; "great, most helpful, but I can not find all of these values on the side of the bottle".
This will always be the case for the 'Hardness' and 'Alkalinity' values as they need to be derived and we will show you how to do that below, can frequently be the case for 'pH', and is sometimes the case for the 'dry residue' value. If necessary visit the manufacturer's website, or drop them an email asking for the data.
The next step is to understand why these values are important to coffee preparation
A value from 1 (strong acid) to 14 (strong alkali), with a value of 7 being 'neutral'. It is not a linear scale, but a logarithmic one, like the Richter scale for seismic activity, so even small movements away from the neutral value of 7 quickly become quite acidic or alkali.
Alkaline water can result in dull, chalky, flat coffee. Acidic water creates bright, imbalanced coffee. You want to use water that is 'neutral' for the preparation of coffee.
As the name implies it measures the solids dissolved in the water. If too many solids are already dissolved in the water it becomes a weaker solvent and will not extract enough solubles from your coffee. Coffee made with water that has a very high TDS value will taste dull and cloudy. Conversely, water with a very low TDS value produces coffee with edgy, unrefined flavours and exaggerated brightness as the water is a very strong solvent.
The formation of limescale in your espresso machine is primarily due to the presence of calcium and magnesium ions in the water, measured as 'hardness'. For this reason it is possible to have a high TDS value, combined with a low 'hardness' value, and limescale will not readily form in your espresso machine.
Hard water does not result in a poor cup of coffee, but it will scale your boiler quickly. Water with a hardness above 90mg/L will always be reduced to a hardness of about 90mg/L as any hardness above this value precipitates out upon boiling and deposits on the inside of your boiler.
Alkalinity measures a solution's ability to buffer an acid, or its ability to resist becoming more acidic.
It is important to understand that it is quite different to 'alkaline' which is a solution with a pH between 7.01 and 14.
Water with high alkalinity neutralises coffee acids, resulting in less acidic coffee. If alkalinity is too low the coffee will be overly bright and acidic.
How to calculate the alkalinity and hardness values
Bottled waters typically disclose their minerals as mg/L or ppm, rather than mg/L CaCO3 equivalents.
To calculate the alkalinity, multiply the bicarbonate mg/L value stated on the bottle by 0.82.
To calculate the hardness, multiply the calcium mg/L value stated on the bottle by 2.5, and the magnesium mg/L value stated on the bottle by 4.2, then add the two resultants together.
Note: boiler corrosion
Acidic water with low alkalinity can potentially cause corrosion in the boiler of your espresso machine.
Dry residue @ 180C: 130mg/L
So, pH = 7, good
TDS/dry residue = 130, good
Hardness = (Calcium x 2.5) + (Magnesium x 4.2) = (11.5 x 2.5) + (8.0 x 4.2) = 28.75 + 33.60 = 62.35, about right
Alkalinity = (Bicarbonate x 0.82) = (71.0 x 0.82) = 58.22, about right
Finding a bottled water that is suitable is surprisingly difficult, as detailed in the table below;
PLEASE click on the above table to enlarge it, so that it becomes legible
I trust this blog has assisted you in your pursuit for espresso nirvana and the protection of your espresso machine.
If you have any questions please get in touch & we will do our best to find the answer for you.