Beer Math – Water Adjustments

It’s finally a good time to talk about water and how to do some basic adjustments…it might get a little science-y here!

For this month, we’ll look at one of the more common water adjustments, and that’s the sulfate-to-chloride ratio (SO4:Cl). Typically, adjustments are made to accentuate the bitterness of the beer (2:1 ratio); balance between bitterness and matiness (1:1 ratio); or to accentuate the matiness of the beer (1:2 ratio). As with other months, we’ll start off with looking at our base recipe:

Style – IPA
OG – 1.060
Efficiency – 72%
Volume – 20L
Pale malt – 4.54kg
Munich 10 – 0.57kg
White wheat malt – 0.28kg
Caramel 60 – 0.28kg
Total grain weight – 5.67kg

Before we get too far along in this, we need to know how much water we’ll need to make this 20L batch of beer. The formula we’ll be using is as follows:

L of Water = Batch Size + Boil Off + Absorption + System Loss + 10% Safety

Batch Size – the batch size of beer we’re making, or, what goes into the fermentor
Boil Off – how much volume is boiled off during the boil (this will depend on your system, but let’s assume it’s 4L/hour, and we’ll boil for 1 hour)
Absorption – how much does the grain absorb (typically, this is 0.96L/kg but may vary slightly on your setup)
System Loss – how much volume are we losing elsewhere in the system such as trub, chiller, evaporation, etc. (for the sake of this example, let’s use 1.5L, but it could vary greatly depending on your setup)
10% Safety – it’s always a good idea to have some extra water on hand!

So, putting all that together we get the following:

L of Water = (20L + (4L/hr * 1hr) + (0.96L/kg * 5.67kg) + 1.5L) * 1.1 = 34 L

From this, we can see that to make our 20L batch of beer, we’ll need 34L of water, so that’s how much we’ll be making our adjustments to.

As this recipe is an American-style IPA, let’s use a 2:1 ratio of sulfate-to-chloride to help accentuate the bitterness of the hops. To start, we need to know what the characteristics of our water is. For this example, I’ll be using the latest information from the City of Saskatoon (, and just pulling out a few key constituents, all reported in ppm (equivalent to mg/L):


As we want a 2:1 ratio of sulfate-to-chloride that means we’ll need half as much chloride as sulfate, so we’ll need a total 44.5 ppm of chloride (89 ppm sulfate / 2). Our water already has 13 ppm of chloride, so we’ll need to add 31.5 ppm of chloride (44.5 ppm – 13 ppm) to our water. That seems pretty straightforward, but how do we go about adding that to our water? Brewers have many brewing salts available to them, and calcium chloride is the one we’ll use to adjust chloride (this will also end up impacting the calcium level, and we’ll address that later on).

We also need to note, that the common calcium chloride (CaCl2) brewers use isn’t just calcium and chloride, it actually in the form of a dihydrate so it has some water attached to it, which means it’s actually written as: CaCl2 ⋅ 2H2O. We’ll see why this is important below!

For our example, we need to know how much chloride we’re adding to our water when we’re adding the calcium chloride, so we need to know the molar mass of our brewing salt, using molecular weights of the individual elements, which are found on the periodic table or with a quick internet search.

Ca = 40.08
Cl = 35.453
2H2O = 2 * (1.0079 * 2) + 15.9994) = 36.0304

Molar Mass of CaCl2 ⋅ 2H2O = 40.08 + (2 * 35.453) + 36.0304 = 147.02

Knowing this, we can now determine how much of our brewing salt is actually chloride:

% Chloride = Molar Mass Cl2 / Molar Mass CaCl2 ⋅ 2H2O = (2 * 35.453) / 147.02 = 48.22%

Next, we can determine how many mg of chloride we need to add:

mg Chloride = L of Water * ppm Chloride = 34 L * 31.5 mg/L = 1,071 mg Chloride

Finally, we can calculate how much calcium chloride we’re going to add to achieve this:

mg Calcium Chloride = mg Chloride / % Chloride = 1,071 mg / 0.4822 = 2,221 mg

So, to achieve a 2:1 ratio of sulphate-to-chloride, we’ll need to add 2,221 mg, or 2.2 g of calcium chloride to our 34 L of water.

I noted earlier on that adding this will also increase our calcium levels, so let’s see what our new calcium level will be. First we’ll determine how much calcium was added in mg:

mg Calcium = mg calcium chloride * (molar mass Ca / molar mass CaCl2 ⋅ 2H2O)
mg Calcium = 2,221 mg * (40.08 / 147.02) = 605.5 mg

Next, we’ll convert this into ppm:

ppm Ca = mg Ca / L of Water = 605.5 mg / 34 L = 17.8 ppm

So, by adjusting our chloride levels using calcium chloride, we’ve also increased our calcium levels by 17.8 ppm, which gives us a new calcium level in our water of 60.8 ppm (43 ppm + 17.8 ppm). We can also summarize it in a table as follows:


As with previous months, there’s many different software and spreadsheets out there that will do all of this for you with ease, but hopefully this helps you to understand what exactly they’re all doing in the background.

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