Making water for coffee – Part 3 – Optimising RO Water

Please note that I have a new and improved method to make water for brewing coffee here.

In the last couple of instalments, we looked at a little theory behind coffee water and then how to make up some bottled stock solutions that we can add to RO water to create a water recipe for brewing coffee.

We made 3 stock solutions one to add magnesium, one calcium and one to add alkalinity. We made separate solutions so that we could mix them up to different levels of each of the required constituents.

Recipe 1 – Calcium Only SCAA Spec Profile
In this recipe we’re adding only Calcium and Alkalinity into the RO water. We’ll be adding 2.3ml of Calcium stock solution and 1.8ml of the Bicarbonate solution to each litre of RO water. This results in a water profile as detailed below.

As you can see we’re hitting 78mg/L as CaCO3 Hardness and 40mg/L as CaCO3 Alkalinity. There is a downside to this recipe in that we are over spec on Chloride which can start to cause sourness to creep in to shots at high concentrations (although it’s suggested that this figure is much higher than those we’re hitting here).

Recipe 2 – Magnesium Only SCAA Spec Profile
His recipe is similar to recipe 1, the only difference is we’re adding Magnesium to give the same hardness, bicarb remains the same. To achieve the desired hardness we add 2.8ml of stock magnesium solution and 1.8ml of Bicarbonate solution to each litre of RO water.

Again we’re hitting 78mg/L as CaCO3 Hardness and 40mg/L as CaCO3 Alkalinity. There is a difference as we’re no longer adding Chlorides so this should be a good thing.

Recipe 3 – Fifty/Fifty
This time we’re using a profile recommended by Maxwell from Colonna & Smalls. We will add 1.7ml of Magnesium stock solution, 1.4ml of Calcium stock solution and we’re upping the Bicarbonates 2.1ml per litre of RO water.

We’re pushing the hardness up to around 95mg/L as CaCO3 and Alkalinity to 47mg/L as CaCO3. We’re also adding both Calcium and Magnesium hardness in equal amounts. The Calcium gives the resulting coffee body and creaminess and the magnesium starts adding sweetness. The water starts getting more aggressive so brew rations may need to be adjusted accordingly. We’re also balancing Chloride and Sulphates which is a good thing in the beer brewing world but I have no conclusive evidence as to its effect here.

Limitations

This method is by no means perfect and I’m still working on improvements. In beer brewing there is a big focus on Temporary Hardness vs Permanent Hardness. Temporary Hardness is Calcium/Magnesium that is associated with Carbonates/Bicarbonates, Permanent Hardness is Calcium/Magnesium that is associated to Sulphates/Chlorides. In our example we’re adding Permanent Hardness which I believe is less desirable.

We are also adding in Sulphates and Chlorides which could be affecting taste and also having a negative impact on our brewing gear.

We’re adding nearly twice as much Sodium as recommended by the SCAA specs. Whilst it’s known that a small concentration enhances sweetness it’s not clear what happens when you start going beyond this limit.

Finally, the majority of these additions are Alkaline in their makeup and since RO water doesn’t really have pH as such (as there are only trace amounts of anything in there) we will almost certainly end up with water that it quite Alkaline which is not so desirable. I’ve tried adding acids (as they do in beer brewing) however this tended to result in coffee that lacks body and depth of flavour.

On the whole using this method I was able to make water that produced coffee that was more to my preference to my tap water (filtered) and also all brnds of bottled water that I could get my hands on with decent profiles. It also gave very consistent results where tap and bottled water changed quite a lot from sample to sample. This is certainly room for improvement and I’ve got some thoughts around that which I’ll explore later.

Finally, if you are interested in other recipes then post below and I’ll get them added in.