Friday, 28 September 2012

Coffee Water Quality - Post 2.

Back in January I wrote my first post on this topic. Water was to me, as it is to most baristas initially, a very grey area. It is now eight months later, during which time I've tried (with a modicum of success) to gain some clarity, primarily through reading (many times!) the SCAA Water Quality Handbook. It was a complex subject for a chemistry-phobe like me to grasp, for several reasons, including:
- Words. Carbonate System, ions, buffer, hydrogen bonding, idealised icosahedral clusters(!!)
- Symbols. 

- Abbreviations.  NaHCO3.    Na+.    CaCI2.    MgSO.  WTF?

In addition, whilst many coffee topics have been discussed in great detail over the years in forums, blogs and articles, there seem to be very few predecessors who have written about water. Jim Schulman's Insanely Long Water FAQ is quite a seminal post, with fantastic info, but I found that again the words/symbols/abbreviations made it difficult to understand.

Now that I've gained a basic understanding, I realise that there is a need for a beginner's guide to water quality, written in a way that helps simplify some of the chemistry. A caveat here though. It is impossible to properly understand coffee water quality without learning some basic chemistry, so what I'm about to write is certainly not everything you need to know, and the simplification process requires some key information to be omitted. My aim is just to share enough info to help others make the first step, so they can then continue to learn more on their own.  Also, my own understanding is still incomplete & probably inaccurate, so if anyone would like to correct anything please do so. To understand this topic more fully, please buy and read the handbook from the SCAA website.
OK, here goes.

What is water?
You've heard of H2O. The abbreviation refers to the two components of completely pure water, hydrogen and oxygen. Nothing else. So immediately many will think "hang on, hydrogen and oxygen are gases". Correct. Actually, we need to think smaller. They are atoms, or rather bunches of hydrogen and oxygen atoms. And when those bunches meet, they stop being a gas and become a liquid. Water.
But you've probably never come across pure water. It is probably the most recycled substance on the planet.  The water we drink has picked up lots of other things along the way. What things? Good question. The simple answer is, things that change the flavour of your coffee. Some good things, some bad things. And those things appear in different quantities depending upon where the water came from and what has happened to it.  Some water is quite pure, with very few things, other water is full of the things. And the things appear in different proportions too. So no two waters (from two different sources) are the same. Hence no two coffees will taste the same if you use different water.

Let's call these things 'solids'. 

Some over-simplified definitions.
So what are these solids??  OK, a little basic chemistry. Atoms and molecules. Stay with me, now! An atom is the basic building block of EVERYTHING. Put a few atoms together and you have a molecule. So everything is made up of atoms and molecules, bunching together like magnets. That's an important concept. There are different combinations of atoms and molecules, and each different combination makes something different. For example, hydrogen and oxygen make water. Table salt is a combination of sodium and chloride. Whoah, whoah!! what are those things? It doesn't matter for now. Just think of everything in the world being make up of different structures of molecules. So salt tastes like salt because of its molecules. Chocolate tastes like chocolate because it has other molecules. etc etc.  And very small changes in the molecules can have a big impact upon what something tastes of.
Great! Now we understand why things taste differently too. But let's get back to water.

Total Dissolved Solids (TDS)
So water consists of hydrogen, oxygen, and other solids. This is probably sounding familiar. Coffee people have heard of measuring water TDS, which is a basic way of expressing how pure, or unpure the water is. How many 'things' are in there.  And recently in the UK some baristas have begun measuring their water TDS, and trying to use water with a particular quantity of solids... around 150ppm (parts per million) is the target, coming from the SCAA guidelines.  The theory is that if you have too many solids (eg 300ppm) or two few (eg 30ppm) then the coffee will not brew correctly and will taste bad... or not taste as good as it could, anyway. (More on why this would be the case later.)

Quality-focused baristas seek to improve the water they have available to them, through different types of water treatment. But in truth few of us currently understand what kind of treatment we need. If TDS is high, we seek ways to reduce it. If TDS is low, we generally just accept it. Reverse Osmosis systems have been developed, which purify water very effectively.  I have not found anyone who has published details of their RO setup... what exactly it does to the water, which solids it removes, which solids are left behind, which additional pieces of the puzzle they have incorporated etc. It remains a bit of a secret at this stage, which is a little unhelpful to the barista community, who are still trying to get their heads around TDS.

So this is about as far as baristas seem to have got in the UK.

A closer look at Total Dissolved Solids
TDS is actually a very blunt way of describing these things in our water. It is a catch-all. I wouldn't say it is meaningless... that would be going too far, as it is a helpful statistic... but two waters could have the same TDS and still be completely different. One would make an exceptional coffee, and the other would make a cup of brown swill. This is due to the different ratios of all the different solids in there.

So we need to break this down further, if we really want our water to be perfect for brewing. And the SCAA have already done that part for us.

(NB some units of measure can be used interchangeably. One mg/L - milligram per litre - is exactly the same as one ppm - part per million.)

The above chart isn't perfect but it gives us some key info.  So there's the 150ppm right in the middle. I'm going to ignore odor and colour because the majority of drinking water in the UK comes via a regulated mains water supplier, and they ensure that there are no smells or colour taints. The 150ppm is broken down into:
(a) Calcium Hardness: 68ppm
(b) Alkilinity: 40ppm
(c) Sodium: 10ppm
(d) Other: 32ppm
Total = 150ppm

Item (d) is the reason the chart isn't perfect, in my view. 32ppm is quite a big unexplained number and if anyone could enlighted me as to why the SCAA have not commented on it then please feel free to comment below. I would imagine that 32ppm of other solids would affect the brewing process somehow.

What about pH?
It's all about balance. Think of a see-saw in a playground. On one side is Acidity. On the other side is Alkalinity. They are opposing forces. This is pH, and it is measured on a scale of 0-14.
- When they are evenly balanced then the water is neither predominantly acidic nor predominantly alkaline. Neutral pH is at the centre point of the scale, and measures 7.0
- If Acidity is greater (than alkalinity) then the see-saw tips in its favour. pH drops below 7.0, and the lower the pH the more acidic the water is.
- If Alkalinity is greater, pH is higher than 7.0 and the closer it is to 14 the more alkaline the water is.
So the SCAA Guideline is 7.0, right in the centre. 

Acid? Alkaline? This is water, isn't it?
Don't think of it that way. As I said above, no two waters are the same. Some waters are acidic, some are alkaline. The coffee will taste different for each.

So what makes it acidic or alkaline?
It comes back to the balance of items a, b, c and d shown above.
- Calcium Hardness contributes to acidity. Infact it is not just Calcium contributing to acidity. Magnesium is another factor, and others. But Calcium plays a bit part in drinking water. (Calcium is a metal mineral that we can ingest in small quantities, like iron.)

- Alkalinity is self-evident. Several things contribute to alkalinity, including hydroxide and bicarbonate.
- Sodium also increases alkalinity.

Do the math(s)
So on one side of our see-saw we have 68ppm of acidity.
On the other side we have 50ppm of alkalinity (40+10).
But we know that the SCAA Target water has a neutral pH of 7.0, so there may be another 12ppm of alkalinity within the 'other' things in there, coming from something else. (But see note 1 below.)

How we can use this information
If you own a TDS meter, great. But how do you know what your Calcium levels are? Perhaps your Calcium is 90ppm, which is too high. You certainly don't want to add MORE calcium to your water.  So we need to be able to measure the acidic Calcium Hardness part of our TDS total. We also need to know the amount of alkaline solids.

Thankfully there are ways to measure these. A simple (if not the most accurate) solution is to use test strips like the ones used by aquarium and swimming pool owners, readily available at low costs on ebay. Search for Calcium Hardness Test Strips, and also KH Test Strips... KH is an abbreviation for Carbonate Hardness, which is just another way of referring to those solids mentioned above that contribute to alkalinity.

Then we look for water treatment that fits the bill. For example, I have in the past used water with a TDS of around 90ppm, and a pH of around 6.8 i.e. slightly acidic. A Calcium Hardness test strip revealed around 60ppm of Calcium, which is close to the SCAA Guideline of 68ppm, which is good. So if I wanted to increase my TDS to 150ppm, I would NOT want to add more calcium, as that would make the water more acidic, when actually I wanted to make it LESS acidic... i.e. get closer to a pH of 7.0 by adding alkalinity. So I would need some sort of water treatment cartridge that increases hydroxide or bicarbonate by around 30-40 ppm.  That's the theory. I hope that makes sense and that I haven't lost you in the words and abbreviations.

Why do these ratios of water 'things' affect coffee brewing?
Many of us think that brewing coffee is just using hot water to wash off coffee particles from the beans, but that isn't the whole picture. Remember those molecules bunching together like magnets? Well the hot water causes chemical reactions to occur. Molecules in the coffee and the water become 'lively' because of the heat, and they begin to jump from place to place, magnetising themselves to other molecules of water/coffee. This creates a variety of different structures of molecules, and as mentioned earlier in this post, different groupings of molecules create different flavours.
So the 'ingredients' i.e. the solids that are in the water, affect this process.Having too much alkaline bicarbonate, for example, makes the coffee taste flat. (See the handbook for more details on this.)

End of part 2!
As always, still much more to learn. But I hope this has helped in some small way and if I can answer questions then I will. There is a lot more info beneath this that it wasn't possible to include in this post. Maybe if there was one thing I might suggest to anyone looking for advice, it would be to find out more about the different types of water treatment on the market, and what they do to the water. Some use technology that the water handbook says is detrimental to coffee brewing! What does yours do, and what do you want it to do? This information is difficult to find out from websites, but I've found the guys at companies like 3M to be very open to discussing such things.

 Notes
1. I have over-simplified the way acidic and alkaline solids balance out to achieve a pH of 7.0.  There is an effect called Buffering which means that 10mg of acidity and 10mg of alkalinity do not necessarily balance out. Hence in the example above, I think (although I may be wrong!) that the 68mg/L of acidity and the 40-50mg/L of alkalinity may actually balance out to produce the displayed pH of 7.0

1 comment:

  1. That's such an informative post with well explanation.

    ReplyDelete