Understanding the Mash pH
Residual Alkalinity and Mash pH
Before you conduct your first mash, you probably want to be assured that it will probably work. Many people want to brew a dark stout or a light pilsener for their first all-grain beer, but these very dark and very light styles need the proper brewing water to achieve the desired mash pH. While there is not any surefire way to predict the exact pH, there are empirical methods and calculations that can put you in the ballpark, just like for hop IBU calculations. To estimate your base-malt-only mash pH, you will need the calcium, magnesium and alkalinity ion concentrations from your local water utility report. Unfortunately, you rarely want to brew a base-malt-only beer.
To estimate your recipe mash pH, you will need the calcium, magnesium and alkalinity ion concentrations from the water report, plus the approximate color of the beer you are trying to brew.
In 1953, P. Kohlbach determined that 3.5 equivalents (Eq) of calcium reacts with malt phytin to release 1 equivalent of hydrogen ions which can "neutralize" 1 equivalent of water alkalinity. Magnesium, the other water hardness ion, also works but to a lesser extent, needing 7 equivalents to neutralize 1 equivalent of alkalinity. Alkalinity which is not neutralized is termed "residual alkalinity" (abbreviated RA). On a per volume basis, this can be expressed as:
mEq/L RA = mEq/L Alkalinity - [(mEq/L Ca)/3.5 + (mEq/L Mg)/7]
where mEq/L is defined as milliequivalents per liter.
This residual alkalinity will cause an all-base-malt mash to have a higher pH than is desirable (ie. >6.0), resulting in tannin extraction, etc. To counteract the RA, brewers in alkaline water areas like Dublin added dark roasted malts which have a natural acidity that brings the mash pH back into the right range (5.2-5.6). To help you determine what your RA is, and what your mash pH will probably be for a 100% base malt mash, I have put together the following nomograph that allows you to read the base-malt-mash-pH after marking-off your water's calcium, magnesium and alkalinity levels. To use the chart, you mark off the calcium and magnesium levels to determine an "effective" hardness (EH), then draw a line from that value through your alkalinity value to point to the RA and the approximate pH. The effective hardness is not the same as the "Total Hardness as CaCO3" you may see on your water report, it is a calculation of the effect that calcium and magnesium have on alkalinity.
After determining your RA and probable pH, the chart offers you two options:
a) You can plan to brew a style of beer that approximately matches the color guide above your RA, or
b) You can estimate an amount of calcium or bicarbonate to add to the brewing water to hit a targeted residual alkalinity, one that is more appropriate to the color of the style you want to brew.
I will show you how this works in the following example.
Determining the Beer Styles That Best Suit Your Water
1. A water report for Los Angeles, CA, states that the three ion concentrations are:
Ca (ppm) = 70
Mg (ppm) = 30
Alkalinity = 120 ppm as CaCO3
2. Mark these values on the appropriate scales. (Denoted by red and green circles here.)
3. Draw a line between the Ca and Mg values to determine the Effective Hardness. (Denoted by a red square.)
4. From the value for EH, draw a line through the Alkalinity value (green circle) to intersect the RA/pH scale. This is your estimated base-malt-mash pH of 5.8 (blue square).
5. Looking directly above the pH scale, the color guide shows a range of color which corresponds to most amber, red and brown ales and lagers. Most Pale Ale, Brown Ale and Porter recipes can be brewed with confidence. The amount of acidity in the specialty grains used in these styles should balance the residual alkalinity to achieve the proper mash pH (from 5.8 down to 5.2-5.6, depending on the darkness of the recipe).
Determining Calcium Additions to Lower the Mash pH
But what if you want to brew a much paler beer, like a Pilsener or a Helles? Then you will need to add more calcium to balance the alkalinity that your malt selection cannot.
1. Go back to the nomograph and pick a point on the RA scale that is within the desired color range. In this example, I picked an RA value of -50.
2. Draw a line from this RA value back through your Alkalinity value (from the water report), and determine your new EH value.
3. From the original Mg value from the report, draw a line through the new EH value and determine the new Ca value needed to produce this effective hardness.
4. Subtract the original Ca value from the new Ca value to determine how much calcium (per gallon) needs to be added. In this example, 145 ppm/gal. of additional calcium is needed.
5. The source for the calcium can be either calcium chloride or calcium sulfate (gypsum). See the following section for guidelines on just how much of these salts to add.
Determining Bicarbonate Addition to Raise the Mash pH
Likewise, you can determine how much additional alkalinity (HCO3) would be needed to brew a dark stout if you have water with low alkalinity.
1. You determine your initial RA and base-malt-mash pH from your water report, and then determine your desired RA for the style you want to brew. In this example, I have selected an RA of 180 (base-malt-mash pH 6), which corresponds to a dark beer on the color guideline.
2. The difference is that this time you draw a line from the desired RA to the original EH, passing through a new Alkalinity.
3. Subtract the original alkalinity from the new alkalinity to determine the additional bicarbonate needed. The additional bicarbonate can be added by either using sodium bicarbonate (baking soda) or calcium carbonate. Using calcium carbonate additions would also affect the EH, causing you to re-evaluate the whole system, while using baking soda would also contribute high levels of sodium, which can contribute harsh flavors at high levels. You will probably want to add some of each to achieve the right bicarbonate level without adding too much sodium or calcium.
Note: The full size nomograph now contains an approximate numeric correlation to beer color (SRM scale). This is intended to better help you target a residual alkalinity level based on the color of the beer style, but it is an approximation. There is a lot of variation in the malt-acidity to malt-color relationship. [Oct.'06]
New and Improved Residual Alkalinity Spreadsheets! (Feb. 2011)
Click Here to download an Excel spreadsheet that makes the same calculations (US units, Version 3.0).
Click Here to download an Excel spreadsheet that makes the calculations in metric. (SI units, Version 3.0).
Note: This version corrects the amount of potential contributed alkalinity as CaCO3, assuming that all salts dissolve in the wort. Unfortunately, in the real world this does not always happen. But this version gives you a benchmark for best case scenario. Chalk is not very soluble, even in the mash at a pH of 5-6.