Monday, 30 January 2012

Coffee Water Quality

This is something that has been weighing on my mind lately. It just feels like such a massively under-considered area. So much time and effort go into other coffee parameters, but when it comes to water I've found it really difficult to get much traction in conversations with others (apart from John Gordon, who seems to have dedicated a good portion of time to understanding the issues and also some options for addressing the problems he experiences). I am frequently advised to dismiss my water concerns, for one reason or another. It's not something I need to think too much about, apparently. Whatever the issues I have, I should address them through one or all of the following:
  • Adjusting my extraction technique to compensate
  • Installing the same filtration and softening systems as everyone else
  • Using bottled water (not very practical in a commercial setting, huh?)
  • Ignoring it. The SCAA water quality guidelines are outdated, they say,

I can't accept this, I'm afraid. That's not to say that the above are incorrect. Nor that they are correct. My point is, the whole issue is spoken about in such a blasé manner. Opinions are thrown around without a care in the world for whether they are based on any scientific evidence. It is just incredibly incongruous to be so laid back about this brewing parameter, in an industry where people are obsessive about things such as the normal distribution of hole-size in a portafilter basket!

Why the pushback?
But I think I know why people sweep it under the rug. I've attempted a few times in the past to get my head around water quality, and given up. Here's an extract from the first section of Jim Schulman's fantastic article on the subject:

Hardness is the term for the calcium or magnesium carbonate dissolved in water as Ca++, Mg++, and HCO3- (bicarbonate) ions. There are two measures of water hardness, hardness and alkalinity. Hardness measures the amount of positive calcium and magnesium ions; alkalinity the negative bicarbonate ions. Both measures are usually given in calcium carbonate, i.e. scale, equivalent units (abbreviated as CaCO3). This means when one unit of scale precipitates out of the water, hardness and alkalinity measured in CaCO3 units go down by one unit each.

I believe this illustrated that water chemistry is a very dry topic to a non-chemist. Most people in the coffee industry (certainly in the barista arena) are not accustomed to this level of science. Sure, we can proudly consider ourselves geeky and be proponents of coffee brewing as a science, not just an art. But it is rare to find someone who is happy to work as a barista for £8 per hour, and yet is also willing (or even able) to muster the concentration and willpower it takes to get a mental foothold on this topic.

The issues
So backing up a bit, just what are my concerns about water? Well at this stage I don't know what I don't know. I have suspicions, based upon some things I have read on the topic of coffee water quality. I'll continue...

Quality. Purity. What do they mean? In simple terms it seems to mean that there are very few particles (solids) within it other than the H2O itself. Particles might be minerals/metals, such as calcium, iron, potassium, and also things like faecal bacteria (yes... poo!) and substances that affect colour. (Click here for an explanation of ten key parameters in water quality, according to the Drinking Water Quality Regulator) We often hear talk in our industry of ideal water quality measured in parts per million (also known as micrograms per Litre mg/L) ... somewhere around the 150ppm mark is usually touted as good for coffee (although opinions differ). In many parts of the UK, and certainly in the UK's coffee capital of London, water is NOT pure. It is nasty, horrible, recycled piss and the taste of it confirms this. It has a high ppm (something like 300ppm in London). It is also very 'hard' (see below). This has an adverse effect upon coffee taste, as well as damaging coffee brewing equipment such as espresso machine boilers, which quickly develop scale. So to be fair, a good deal of work has gone into providing commercial equipment that can filter out some of this crap and also soften the water, so that problems like scale are reduced.

But where I live, the water is generally very pure, and very soft. Too pure and too soft... maybe. Very soft water has a high pH level – which is a measure of the water's acidity. Soft water does not cause as much scale in coffee equipment, so that's a good thing. But the acidity can apparently cause corrosion of parts, which is just as bad... perhaps worse if it means that corroded metal ends up in your cup of coffee! So does this mean we should increase the mineral content of pure, soft water that we want to make coffee with? I believe the answer is yes, but so far haven't had a great deal of support for this... either from baristas, coffee suppliers, or indeed water treatment specialists... which I suspect is for the reasons already mentioned.

And then there's the impact of that pH level upon the physical extraction of the coffee. Some say that soft water enables more effective diffusion of coffee particles from the grinds, so can result in overextraction if not carefully managed. Some say the opposite(!) - that soft water makes extraction LESS effective.

And even if you get the extraction right, what is the effect of this very pure water upon taste... will the coffee be overly bright and acidic? And therefore will the coffee flavour not match the experience of the roaster when he/she sampled and selected the beans, or when they were profiled and roasted? I don't want to pay good money for beans that could taste of peaches and cream, only to find that the water I'm using makes them taste of lemons and limes. Is this likely? I don't know, and despite some fantastic articles out there, I haven't yet found anyone who can give me an answer that I trust is relevent to my own local water issues, based upon science rather than supposition.

And even once I eventually understand and arrive at my own conclusions, there's the problem of finding appropriate treatment systems at an affordable price. Treatment systems seem to want to 'filter out', rather than 'add back'. For example, this presentation by boiler manufacturer Marco has some excellent points on the subject of water quality, but at the end refers only to filtration.
I know there are water additive solutions out there, but since I haven't found anyone who uses them, this raises all kinds of doubts as to whether they are really needed, whether they are any good, or whether they are readily available.

And this is, I'm sure, only part of the equation.

I've a long way to go on this subject, it seems.
Read the follow-up post on Coffee Water Chemistry written 9 months later.


  1. I live on a private estate with its own natural water supply. Ive not measured the TDS etc but I can tell you it is clean and delicious to drink. Yes We get scale in the kettle and round the taps, so I suspect it is full of minerals. I run this lovely water through Brita filters prior to being placed in the espresso machine or kettle, how effective this is I dont know, but de-scaleing a dual-boiler is something I dont want to do if I can help it.

    Inside Brewtus's watertank is a water softener, I had no idea you were meant to recharge it thoughts were replace every 12 months...but Expobarista alerted me to the process of recharge in salt water. So couple of weeks ago I did just that, Since then I have noticed that espresso is more sour & seemingly harder to extract?! Could it be stripping away all those minerals through two layers of filtration is effecting the result in the cup? Ive not changed anything else so it leaves me wondering....

    1. It might pay you to contact your local water quality regulator or water supplier to find out the various readings shown in the first (SCAA) diagram above, Gary. I've done that and was surprised at the results (a future follow up blog post!)
      Wish I knew more about all this and could help out. I've ordered the SCAA Water Quality Handbook to help me learn, so if I find out anything I'll let you know. The Brita thing is an extra complication, perhaps. I have no idea what it is filtering out, or what it is designed to do other than 'filter', which is a bit of a meaningless term. And 'double filtering'... it's got to affect the taste of the coffee, I think.
      I am surprised though that the result of recharging the water softener is that the espresso is more difficult to extract, when softer water is meant to do the opposite. The sourness might also point to underextraction, as you know. This is precisely why I think it's so important that we get a better grip on our understanding of brewing water. "it leaves me wondering...." is exactly how I feel, and it's just not good enough, is it?

      BTW, Just moved home this week and the water in our new private supply has been approved by the relevant authorities. The problem is it tastes rubbish as a straight glass of water. Just goes to show, just because water is approved for drinking doesn't mean it's GOOD for drinking... or indeed for coffee!!
      Cheers, Gary.