I’ve long been interested in the quality of the water we use both at the Roastery, and also that used by our customers. I wrote a post back in 2012 where I tried to sum up the issues we faced and another post shortly afterwards which compared the water we have to the ‘good’ coffee water. I’ve dabbled with this issue on and off since then, trying out varying approaches, and water filter options in an effort to arrive at a ‘solution’ to the problem.
In August this year ‘Water for Coffee’  was published, a book which has helped fill in a number of gaps in terms of my understanding of the impact of water on coffee. Having failed my Chemistry O Level (twice!) I cannot claim to have fully understood the Science behind the concept but I have enjoyed experimenting with some of the practical knowledge I have gained.
Fundamentally the book has helped reinforce my original notion that soft water does have an impact on coffee, though not necessarily in the way I had imagined. The book itself does a much better job of explaining all of this and I would urge anyone with an interest to have a read, but in practical terms I have found myself focusing on three things:
Firstly, there is the presence of the minerals magnesium and calcium (or the lack of them in the case of our water at the Roastery). Both these minerals have flavour carrying properties so a lack of them can make it difficult to pick up the interesting flavours in our coffee. In recent weeks I have cupped the same coffees using our tap water alongside water with added magnesium, and it is much easier to pick out the flavour profile of the coffee. Unlike calcium, magnesium will not cause scale in our equipment, hence choosing to add this mineral.
This week, when I tested the water at our Roastery I measured a general hardness (GH) of 4.8ppm , which is one of the lowest I have experienced here. Ideally we need to be looking at a GH of between 50 and 175ppm.
We then need to consider alkalinity. This is where my understanding struggles in a chemical sense so I like to think of an analogy:
Imagine a scenario where acid rain falls on a stream where bicarbonate levels are good. This bicarbonate acts as a buffer, neutralising the acidity and protecting the life in the stream. Compare that with a stream where there is low bicarbonate; no buffer exists and the acidity of the stream is increased, potentially causing damage to life.
We need bicarbonate in our coffee water to act as a buffer to the acidity of the coffee.
When I tested the water at the Roastery this week I measured bicarbonate levels of 6.1 ppm (HCO3). The ideal levels of bicarbonate should be between 40 and 75 ppm (HCO3).
Finally we need to consider the pH of the water. Water with a neutral pH or a slighlty base pH will be best for coffee, particularly in terms of extraction. Currently the water at the Roastery has a pH of 6.95 (slightly acidic).
In practical terms the water at our Roastery changes the character of coffee. We have already noted how the lack of minerals makes it difficult to determine flavour. Over the years we have also noticed that extraction can also be inconsistent and often we see a lot of channelling in the coffee bed. More recently we have discovered that our water can produced a heightened acidity or sour note in the coffee and we are beginning to realise that our water can mask the roast degree of our coffee.
Over the past four years we have worked hard to develop the quality of our coffee roasting. We are become more knowledgeable in respect of green bean selection and are now monitoring the moisture content of our unroasted beans (this will form the basis of future posts). We carefully track and monitor all our roasts, and regularly taste our coffees to determine whether our roasting is reaching the high standards we set for ourselves. Our understanding of the impact of water on coffee is a crucial part of developing our roasting. We need to be certain that the characteristics and flavours we experience when we taste our coffee are a result of the roasting and are not being influenced by the water. While our water at the Roastery is nowhere near ideal for coffee, we have customers who have more balanced water and we need to know how they are experiencing our coffee.
As well as developing a better understanding as to the nature of the problem, we have been working hard to develop a solution which allows us to taste our coffee using as near to ideal water as possible. We’ll explain a little bit more in the next post.