Revisiting Hamilton’s Tap Water (For Accuracy)

Recently I have been playing with mineralizing distilled water to different GH:KH ratios to see how it affects coffee flavour using the ideal brew water chart from Water for Coffee as a guide and one of Matt Perger’s water recipes (found in the comments here) as a starting point. While doing so, I came across more up-to-date information that makes it necessary to re-examine my two previous posts. The purpose of this post is to explain the changes and then perform this quick re-examination.

My experimentation led me to a lot of math, learning about moles, dilution calculations, and summarizing things in equations. After all of this I couldn’t seem to reconcile Perger’s water recipe with the ideal brew water chart, although this recipe typically produces pleasant coffee. Perger said this recipe should lead to 100 ppm Mg and 50 ppm KH. Whichever way I did the math it added up to 24.5 ppm Mg and 62.1 ppm KH.

Since I was confident in my math at this point, I concluded that maybe Perger wasn’t trying to hit the ideal realm of the brew chart, or that he mistakenly based his math on the chart as though it were presented in ppm with [ion] as [CaCO3], and it tasted good anyway. It turns out that the second conclusion was closer to the truth. But it wasn’t Perger’s mistake.

After a bit of research and reading through coffee’s deep web, I decided to go right to the source and ended up having a short Twitter exchange with Chris Hendon. As it turns out, the ideal brew water chart presented in WFC is presented in ppm with [ion] as [CaCO3] as opposed to [ion] as [ion], despite the book’s advocacy for the use of [ion] as [ion]¹ as the standard for ppm measurement.

This means that my previous two blog posts about Hamilton’s water as it relates to coffee brewing must be re-examined. The data from those posts are correct, however the analysis of the data assumes that the brew chart is presented with ppm as [ion], which is not what we want if we are working with the ideal brew water chart from WFC.

Thus, let’s re-examine.

Testing Hamilton’s Tap Water (For Coffee)
Here is the data presented with [ion] as [CaCO3]:

Mar 17, 2016 – Mg: 65.6 ppm, Ca: 87.5 ppm, KH: 91-93.4 ppm
Mar 18, 2016 – Mg: 32.8-49.2 ppm, Ca: 87.5-92.5 ppm, KH: 93.4 ppm
Mar 19, 2016 – Mg: 65.6 ppm, Ca: 87.5 ppm, KH: 88.5 ppm
Mar 20, 2016 – Mg: 82 ppm, Ca: 93.8 ppm, KH: 91 ppm
Mar 21, 2016 – Mg: 65.6 ppm, Ca: 87.5 ppm, KH: 93.4 ppm
Mar 22, 2016 – Mg: 65.6 ppm, Ca: 81.3 ppm, KH: 93.4 ppm
Mar 23, 2016 – Mg: 82 ppm, Ca: 93.8 ppm, KH: 93.4-98.4 ppm

Average – Mg: 63.6 ppm, Ca: 88.9 ppm, KH: 92.9 ppm

Within this sample set our Mg content fluctuates notably, while Ca and HCO3 (KH) remain fairly constant. If we look at our average reading, we get a GH of 152.5 ppm and KH of 92.9 ppm. In this sample set, our GH varies +/- 30.9 ppm and our KH varies +/- 5 ppm.

In short, our GH will generally be within the ideal range of the ideal brew water chart and the KH will still be pretty far from ideal. Thus, Hamilton tap water may leave our coffee flat and chalky, which is the same conclusion as before. Ideally our water filtration would bring KH levels down to somewhere between 32.5 ppm and 75 ppm while leaving our GH levels (Mg and Ca) relatively the same.

Filtering Hamilton’s Tap Water (For Home Brewing)
The data with [ion] as [CaCO3]:

Tap water – Mg: 49.2 ppm, Ca: 81.3 ppm, KH: 91 ppm
Brita filtered tap water – Mg: 49.2 ppm, Ca: 68.8 ppm, KH: 32 ppm

The tap water in this second test is similar to some of the data from the first test. The tap water had a GH of 130.5 ppm and KH of 91 ppm. After Brita filtration the GH was 118 ppm and the KH was 32 ppm. These results actually put us right on the border of ideal and acceptable water in the ideal brew water chart.

Conclusion
If you brew coffee in Hamilton, the Brita filter should take your tap water from poor for brewing to acceptable or ideal for brewing, depending on the tap water that day.

 
¹The difference is discussed in the corrigendum to the book posted here on 10-10-15.

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