Water Quality
Your cup of coffee consists of around 98% water – so it’s not surprising that water quality can have a large impact on the coffee we taste in the cup.
This article will help you understand how water can impact the taste and aroma of brewed coffee and also your coffee brewing equipment.
Water Composition
Water composition is complex – the two main parameters of interest to us for brewing coffee are water hardness and alkalinity.
Parameter 1 – Hardness
Hardness is the amount of dissolved calcium and magnesium in the water.
Parameter 2 – Alkalinity
Alkalinity is the acid buffer capacity of water
How does our water acquire hardness and alkalinity? At the beginning of the water cycle, water vapour in the atmosphere reacts with carbon dioxide to become slightly acidic. The acidic rain encounters carbonate rock in the ground and acquires magnesium and calcium minerals (hardness) and hydrogen carbonate ions (alkalinity).
The hardness and alkalinity of your water will vary depending on the geology where you live. In London where the geology is chalky limestone, the water is very hard and not ideal for brewing coffee. In Edinburgh where the ground is hard rock the water acquires little calcium and magnesium and remains soft.
Impact on Aroma and flavour
Hardness and alkalinity affect the aroma and flavour of coffee in the cup.
Hardness
Hardness affects extraction efficiency. Higher hardness of a water, the higher the extraction efficiency.
Alkalinity
Alkalinity affects the perceived acidity of a coffee. The higher alkalinity of a water, the lower the perceived acidity of the coffee.
The SCA Water chart reproduced here has hardness on the vertical scale and alkalinity on the horizontal scale. Any waters hardness and alkalinity can be measured and it can be placed on this chart. The impact on flavour can also be seen on this chart. As we increase hardness, our coffee brew can tend from under extracted to over extracted, with an ideal zone between. Similarly, as we increase our alkalinity, acidity tends from sharp and sour to flat, with an ideal zone somewhere in the middle.
Impact on Equipment
Water hardness and alkalinity can cause two problems in our kettles and brewing equipment.
- High hardness and alkalinity can lead to Limescale formation
Scale is the chalky deposit that forms in your kettle, or boilers and espresso machines. This leads to a decrease in efficiency of heat transfer and a clogging of valves.
- Low alkalinity can lead to Corrosion
Corrosion is the destruction of a metal by a reaction with its environment.
The SCA Water Standard
The SCA has produced a water standard that both produced high quality coffee and enables a safe operation of equipment. It has limits to hardness and alkalinity and also requires the following:
- Odor free
- Chlorine free
- pH target of 7
We can see the SCA target zone on the chart above.
You should be aware that bottled water isn't necessarily suitable for brewing - because although the water will be odour and chlorine free, it doesn’t necessarily match the SCA requirements for hardness and alkalinity.
Treatment Methods
As most waters from the tap are too high in alkalinity and hardness, water treatment is preferred.
At home, an effort to remove off tastes and reduce hardness can be made using a water filter jug, these typically use an activated carbon filter to remove off tastes and reduce water hardness.
On a commercial level there are a number of possible solutions - including filtration systems or more advance Reverse Osmosis systems.
Now you have your water quality sorted, its time to buy some specialty coffee to try some brews! Have a look at all of our coffees here.
References
- Dr Marko Wellinger Et Al., SCAE Water Chart Report: Measure, Aim, Treat, Zurich University of Applied Sciences
- Dr Marko Wellinger Et Al., SCA Water Quality Handbook Part One: Systematic Guide to Water Fundamentals,
- SCA Coffee Standards, Revised 2018