Ask Mr. Wizard

Utilizing A Brewing Water Calculator


Frank Long — Cooperstown, New York asks,

In the January-February 2023 issue of BYO, you reference your water tool. Can you please shed some light on that?

picture of gypum, calcium chloride salts up front with phosphoric acid in the back.
A quality, high-accuracy scale, a water report, and a well-built water calculator are good things to have on hand if you plan to tweak your water.

Me and my big fingers! Did I type some words about my water tool? While it’s tempting to geek out with water math, I’ll try to keep this answer informative without jumping down the drain. In my opinion, the first step in assessing brewing water is the calculation of residual alkalinity using Kolbach’s method from 1951. While it’s nice to understand the units behind the calculation, it’s not required. Residual alkalinity (RA) = (bicarbonate concentration [mg/L] x 0.046) – (calcium concentration [mg/L] x 0.04) – (magnesium concentration [mg/L] x 0.033). For the sake of discussion, assume we have a water report for our local water and know we have 76-ppm (same as mg/L) calcium, 18-ppm magnesium, and 295-ppm total alkalinity as CaCO3.

We have everything we need to calculate RA, except we need to convert 295-ppm total alkalinity as CaCO3 to ppm HCO3 by multiplying 295 by 1.22. RA = (295 x 1.22 x 0.046) – (76 x 0.04) – (18 x 0.033) = 12.9 °dH (that’s German degrees of hardness, another term that is nice to know about but not required to use the math). Because RA is positive, we know we have alkaline water that will increase mash pH over a standard mash test performed using distilled water. When RA is negative, mash pH is lower than the standard mash. The other thing RA gives us is a magnitude of change; (+) 10 °dH corresponds to an increase in mash pH of ~0.3 and (-) 10 °dH corresponds to a reduction in mash of ~0.3. Looks like our water is pretty darn alkaline and is predicted to drive our mash pH up by about 0.4 pH units! Now what? This is where my water tool helps provide solutions.

There are a few approaches to using this type of water: 1) brew a beer using acidic specialty malts (like roasted or caramel malts) to balance the alkalinity of the water; 2) add calcium and/or magnesium salts to reduce RA; 3) dilute RA with reverse osmosis (RO) water; 4) add an acidulant (usually lactic acid, phosphoric acid, or acid malt); and/or 5) remove alkalinity by boiling and/or treating with calcium hydroxide. These methods, except for the last, are all easy to use for brewers of a wide range of brew sizes, including us homebrewers. And as is the case with many a brewing solution, simultaneously using more than one method is totally cool.

So, that tool you’re asking about combines the approaches listed above, except for alkalinity removal, into an easy-to-use calculator ultimately designed to predict mash pH based on water RA, which we have just calculated, and grist bill. Although mash pH is the process variable most brewers focus on when adjusting brewing water, water components unrelated to pH are also a big deal because they affect beer flavor. John Palmer refers to these components as seasoning, which is really a great analogy. Chloride, sulfate, and sodium targets are entered along with targets for calcium, magnesium, and bicarbonate. The calculations predict mash pH based on the target water profile and grist bill, as well as providing a “water recipe” to use for the brew. When the target concentration of any ion is less than the concentration in the water being treated, RO dilution water volume is calculated.

In addition to knowing the RA of the untreated water, some grist bill basics are needed. This is where mash pH prediction becomes approximate. While the standard malt analytics used to prepare a certificate of analysis (COA) for base malts includes wort pH, special malt data do not. But we do have rules of thumb for how special ingredients like crystal, light-roasted, dark-roasted, and acidulated grains affect mash pH. For each percent of these grain types, pH is reduced by 0.025 (crystal), 0.002 (Munich), 0.03 (light-roasted), 0.05 (dark-roasted), and 0.1 (acidulated) pH units. For example, a mash made up of 95% Pilsner malt with a wort pH of 5.8 (this is from the malt COA), 5% crystal malt, and water with RA = 0 (same as distilled water used for lab testing), will have a mash pH of about 5.68 (5.8 – (5 x 0.025)). The source of this information is from Siebel Institute of Technology’s lectures about brewing water and residual alkalinity and provides the practical brewer with estimates.

In my opinion, the first step in assessing brewing water is the calculation of residual alkalinity using Kolbach’s method from 1951

Let’s assume we are brewing a beer with the water loosely defined above, do not want to add any brewing salts, liquid acids, or RO water, and want the mash pH to be about 5.5. To crunch the numbers, the only two things to consider are RA (12.9 °dH in our assumed water) and grist composition. The water RA tells us our mash pH is going to be pushed up about 0.4 pH units (12.9 °dH / 0.3 pH units per °dH = 0.43) from the lab wort pH (5.8 gets bumped to 6.2), so this brew will either require a big dose of specialty malts with color because light-colored special malts are not very acidic, or we can add acidulated malt to help bring the mash pH into balance. One solution that works out is using 40% base malt, 50% Munich malt, 5% light-roasted malt, and 5% acidulated malt. That grist bill could be a dunkel. Not a bad beer to brew using my example water that just happens to match a reference for Munich water.

But what about brewing a Pilsner with this same water? A great start to this problem is to reduce the very high RA. Calcium additions are an option, but the best water profiles for Pilsner beers have a neutral RA and are relatively low in total dissolved solids (TDS is the sum of all water ions). Adding more salts to the base would simply drive TDS up. The best solutions are either diluting with RO or removing alkalinity. Alkalinity removal is a literal science project and not simple without the requisite set-up, so I am not going to that well.

Diluting with RO water is simple, but target ion concentrations are first required for the calculation. In example 1 below, the calcium target was set to 50 ppm (down from 76) and the bicarbonate target was set to 100 ppm (down from 360). The water tool does the rest, providing base water and RO water volumes, along with required salt additions, options for acid additives, and the profile of the adjusted water. Note that there is still some residual alkalinity because I set the target bicarbonate level down to 100 ppm. The summary below includes a good dose of acid to bring the mash pH down to the target of 5.45.

visual of mr. wizard's water calculator, example 1
Example 1

Using the same water with 12.9 °dH, let’s pivot into IPA territory. Now, we want to know more about water than simply the ions driving pH because IPA water typically has much more “seasoning” than Pilsner water. Per Kunze, Munich well water (source not stated) contains little sulfate or chloride; 10 and 2 ppm respectively. Let’s assume our IPA is brewed using 90% pale ale malt with a lab wort pH of 5.7, 5% wheat malt for added foam stability, and 5% light crystal malt for color. This grist and water combination will yield a higher mash pH than our target of 5.4 because of the high RA.

As high TDS waters are common for classic ales and because our base water has very little sulfate or chloride, a good approach to this beer is to reduce RA by adding a combination of calcium sulfate, calcium chloride, and/or magnesium sulfate. The choice of salts depends on what we want in our profile. The water recipe below is one of many possibilities. The combination of grist bill and water salt additions gets us really close to our target mash pH, while providing a similar adjusted water profile to the mineral-rich waters used in classic ales. In example 2 found below, the predicted mash pH (not shown) is still a bit higher than the target and my water tool suggests the addition of a bit of acid to correct.

To download a copy of Mr. Wizard’s water calculator, click here.

visual of mr. wizard's water calculator, example 2
Example 2
Response by Ashton Lewis.