[Having discovered new information, the data from this post has been revisited here.]
I recently finished reading Water For Coffee by Maxwell Colonna-Dashwood and Christopher H. Hendon, an incredibly insightful book on the importance of water composition as it relates to coffee flavour and extraction. As the book was partly intended to spur discussion about water for coffee, I thought it would be fun to get in on the conversation.
The book focuses heavily on the roles of calcium and magnesium (general hardness, or GH), and bicarbonate (temporary/carbonate hardness, or KH) in determining the flavour in a cup of coffee. Naturally, after reading the book I decided I must buy a titration drop test kit to test my brew water composition. The book recommends titration as an affordable and accessible means of testing one’s water composition relatively accurately. And so I bought the Red Sea Reef Foundation Pro Test Kit, as seen on the Red Sea website and the feeds of every science-enjoying coffee enthusiast on Instagram.
After testing my own brew water I performed an experiment. I took and measured samples of water from my tap at home every day for a week to get a general idea of how the tap water in Hamilton is for coffee brewing so that I could post my results online for whoever may be interested, e.g. local coffee nerds and reefers (the latter apparently as nerdy as us coffee folk).
For those of you who do not know what a titration session consists of: in this case it is when you take vials of water, add specified amounts of specific chemicals, then add more drops of a different chemical until the water in the vial changes colour. The number of drops it takes to reach the end colour correlates to a certain ppm (parts per million) measurement of the measured ion. Very science.
There are three separate tests in the Pro Test kit: Mg, Ca, and KH. The Mg and Ca tests were pretty straightforward, however I had some trouble identifying whether I had reached my end colour with the KH kit, reaching a sort of pale salmon colour rather than the expected murky purple colour. Perhaps had I added more titrant I would have reached the final purple colour; although I did use quite a bit and the colour didn’t seem to change any further. For the sake of conservative estimation, we can interpret my KH measurements as meaning “at least” x ppm. The Mg and Ca tests were much more obvious.
[Edit: After watching Christopher Hendon’s recent video on titration, I have discovered that the pale salmon colour that I described above is, in fact, the correct end colour for the KH test.]
I used 10 ml water samples for all three tests despite the recommended 2 ml, 5 ml, and 10 ml for Mg, Ca, and KH respectively, which, provided I understood the book correctly, will increase the precision of the Mg and Ca measurements (Edition One, page 95). The Mg test measures in 20 ppm increments per 0.01 ml of titrant added to a 2 ml sample, so in a 10 ml sample each 0.01 ml of titrant should correlate to 4 ppm. The Ca test measures in 5 ppm increments per 0.01 ml of titrant added to a 5 ml sample, so in a 10 ml sample each 0.01 ml of titrant should correlate to 2.5 ppm. I believe this is allowable.
The KH test measures in meq/L, which is a unit of measurement that eludes me, so to obtain the measurement in ppm I used this neat little converter that I will just blindly assume is accurate until somebody with more understanding corrects me.
[Edit: The converter was very close to the math from Hendon’s titration video.]
I think it is also important that I mention that, according to the corrigendum posted on the Water For Coffee website on 10-10-15, the Red Sea kit “measures and reports individual ions rather than in [ion] as [CaCO3]” (Chapter 1, page 10). This essentially means that our measurements report ppm for each ion as though each ion were itself, and not CaCO3, which is, surprisingly, a distinction that must be made. As such, no conversions should be necessary for final ppm measurements, as would be necessary for ppm reported in [ion] as [CaCO3].
[Edit: According to Hendon’s titration video, the Red Sea kit reports in individual ions for the Ca and Mg measurements, but in [ion] as [CaCO3] for KH measurements. Since learning this, I have converted the following measurements to display ppm as HCO3 (bicarbonate), as they were originally posted in ppm as CaCO3.]
Anyway, here is the data:
Mar 17, 2016 – Mg: 16 ppm, Ca: 35 ppm, KH: 111-114 ppm as HCO3
Mar 18, 2016 – Mg: 8-12 ppm, Ca: 35-37 ppm, KH: 114 ppm as HCO3
Mar 19, 2016 – Mg: 16 ppm, Ca: 35 ppm, KH: 108 ppm as HCO3
Mar 20, 2016 – Mg: 20 ppm, Ca: 37.5 ppm, KH: 111 ppm as HCO3
Mar 21, 2016 – Mg: 16 ppm, Ca: 35 ppm, KH: 114 ppm as HCO3
Mar 22, 2016 – Mg: 16 ppm, Ca: 32.5 ppm, KH: 114 ppm as HCO3
Mar 23, 2016 – Mg: 20 ppm, Ca: 37.5 ppm, KH: 114-120 ppm as HCO3
Average – Mg: 16.29 ppm, Ca: 35.5 ppm, KH: 113.33 ppm as HCO3
Basically this means that my tap water (our generic Hamilton water sample) is not ideal for brewing coffee, according to the standard set by Colonna-Dashwood and Hendon, as it is too high in KH. The GH (combined Mg and Ca) is ideal for a very narrow set of circumstances, and at least acceptable for a much wider range of circumstances (i.e. if the KH were lower). To give you a good idea how far off our KH is, at this GH we would need our KH right around 37.5 ppm to find ourselves within ideal parameters (although with a higher GH, our KH could be as high as 75 ppm, depending on the GH).
Why does this matter? Well, KH functions as a buffer for the acidity in coffee – it balances out the high amounts of acidity. High enough amounts of KH can make the acidic compounds in a brew function as bases, leaving the coffee tasting flat and chalky.
Luckily my Brita filter seems to do the trick for home brewing, according to the quick, preliminary test I performed while learning to use my titration kit. That is, if the trick is to have acceptable brewing water. It’s still not ideal, but I will be experimenting further.
A few other details for those of you who might be interested:
-Where I accidentally pressed more than one drop of titrant into the test water vial, a range of ppm is given, correlating to the range of drops in which the colour change took place.
-It should be noted that tap water composition will vary from city to city, and will presumably even fluctuate between different parts of the city. This experiment is more to provide an example of the water at some “random” point in Hamilton to give a general idea of what the water may be like in any given part of the city.
-I followed the instructions provided with the kit almost exactly. Apart from my previously mentioned divergences, I did not flush the vials I used with distilled water, but with tap water before and after each test. For our purposes, I think this should be fine.
-I wore yellow rubber gloves for each titration session because some of the chemicals are corrosive and I was scared.
-Hamilton, as in Hamilton, Ontario, Canada.