Have you ever wondered why the same coffee tastes differently at a café than it does at home? My mind has been awash with this question lately, as I have finally had the chance to sit down with one of my Christmas presents - Water for Coffee, by Bath Barista Extraordinaire Maxwell Colonna-Dashwood and Chemist Christopher Hendon.
We get a fair number of customers asking if its worth filtering their water for coffee. If you care about lime-scaling up a water tank, then yes, no question, though there a few way to approach that.
If you are thinking about taste, however, then read on. But to summarise brutally: standard filtered water, using say, a britta filter, will definitely make your brew taste DIFFERENT. But that might not mean it tastes better...
The coffee you are drinking - that vibrant, oily, intensely flavoured dark liquor - is likely over 98% water. Even in a tiny espresso, the actual coffee is only about 10% max, compared to the vast bulk being our humble friend H20. It may not seem the most exciting part of your morning cup of java, but it is a huge contributor to the drink - from how it brews, to the final product.
I am only just starting to soak it up and I certainly am not going to attempt to do it justice. It's a fairly intense book, getting deep into the chemistry of what exactly water is, and what it thinks it is doing when it meets up with coffee.
The stand out points however are:
a) Water is super important to what you end up tasting.
b) There is a lot more to water hardness than just the amount of bits. WHAT bits they are makes an ocean of difference.
Water hardness is something we are pretty conscious of in Guildford, and the UK generally, with such an incredible geological variety in such a short area. We are all used to the idea that a fairly short trip across the country means that we find a totally different tasting liquid coming from the tap.
To summarise, the book highlights three substances key to water hardness as it relates to the coffee brewer:
They all play strikingly different roles.
Calcium rips flavour out of the dissolving coffee and gets it into the cup, Magnesium binds with certain flavouring compounds, and Bicarbonate acts as a buffer, controlling the pH and certain states of the water.
It is not just the amount of these - it's the balance. The relationship between these substances will make the same coffee, brewed the same way, end up as a radically different cup.
A traditional water filter, or a water softener, is thus only a small part of the story. Its not just about taking bits out. Its about which bits you take out, and what you put back in.
This is certainly of HUGE use to the bleeding edge barista and coffee shop owner. There is a lot that is going on to control for this in some shops, and you can expect to see some pretty nifty gear near the water tanks/boiler/staff toilets in some places.
But from the view of the roaster, and the home coffee enthusiast, this is still of supreme interest, even without any fancy reverse osmosis filters. One can certainly play around with mineral water, and combinations thereof to get the perfect water for the way they like their coffee. If you fancy diving into that there is a marvellous discussion on the UK Coffee Forum with some great ideas for fun to be had in the bottled water aisle.
But even if you do absolutely nothing, the key thing to take way is that coffee is not just about where it comes from, or how it has travelled, and (a challenge from the perspective of a roaster) how it was roasted. Where YOU are, where you brew and drink it, is as big a piece as everything else.
If you take your favourite beans on the train and head up from London to Edinburgh you will be drinking far softer water, and a with a very different make-up of key minerals. The same bean brewed with water in Lancashire is going to taste hugely different to the same bean brewed in Kent.