Adjusting Mash pH
Adjusting mash pH is fairly involved, but you can determine what the pH will be using your water's residual alkalinity. By calculating the
residual alkalinity,
using inputs from your water analysis, it can be converted to a relative pH value. Basically, 10 degrees of residual alkalinity equals 0.3 pH units. The equation begins with what a mash pH would be if using distilled water (5.8 pH), and then adjusts it for the effects of three constituents. Those constituents are bicarbonate (which raises mash pH), calcium and magnesium (which lower mash pH). The equation for expected pH is:
pH = 5.8 + [0.028 x {(Total alkalinity(as CaCO3) x 0.056)(Ca (ppm) x 0.04)(Mg (ppm) x 0.033)}]
Note: RA=(Total alkalinity(as CaCO3) x 0.056)(Ca (ppm) x 0.04)(Mg (ppm) x 0.033)
The recommended value for the pH of your mash is 5.25.8. Three things can be done to correct pH. They are (1)specialty grain additions, (2)calcium and magnesium salts additions, and (3)using other water treatments.
Additions of dark grains, crystal (or caramelized grains) and/or highly roasted grains, can drop the mash pH by up to 0.5 points. This may be plenty of adjustment and no more mash adjustments will be necessary. But, when brewing lighter beers, you may use calcium salts like calcium chloride to help adjust mash pH.
After solving the equation for the predicted mash pH with the values from your water analysis, tweak the values for calcium and/or magnesium until an acceptable pH is reached. The values will be in ppm (which equals mg/l). Multiply the weight of calcium in mg/l by the amount of water you need to treat (in liters) to find the milligrams of calcium needed.
To find out the amount of gypsum to add, divide the amount of calcium needed (in mg/l) by the calcium ion percentage in gypsum (taken from table 8.2 in Ray Daniel's book Designing Great Beers),
which is 23 percent (if using epsom salts and magnesium, magnesium's ion concentration is 10%). Since 1000 milligrams equals 1 gram, divide the result by 1000 to find the number of grams gypsum needed.
As an example, if after running the calculations I find that I need 100 ppm (equals 100 mg/l) calcium to get the correct pH for my water:
I have 9.075 gallons of water, so: 9.075 gallons = 34.4 liters and 34.4 L x 100 mg/liter=3440 mg of calcium required.
Next divide by the percentage of calcium in gypsum: 3440 mg / 0.23(23%) = 14956 mg / 1000 grams/milligram = 14.956 or 15 grams of gypsum. Check out Ray Daniel's book Designing Great Beers under the water chapter to learn more about adjusting the mash pH of your brewing water.
 Under "Other Water Treatments", I sometimes use a product called 5.2 pH Stabilizer by Five Star. Here is what the manufacturer says about the product: 5.2 is a proprietary blend of foodgrade phosphate buffers (similar to brewer's salts) that will lock in your mash and kettle water at a pH of 5.2 regardless of the starting pH of your water. Some of the benefits of keeping your mash pH at 5.2 include:
 Optimizing the enzymatic activity of your malt
 Helping clarify your wort
 Obtaining more consistent hop usage in the boil
 Reducing scaling & mineral deposition in all your equipment
 Brewing more consistent beer!
The fact that you are aware of mash pH and its effects on your beer means that you are way ahead of the curve. Get yourself some of the ColorpHast strips and start testing your mash pH. The more aware you are the better brewer you will become.
References: Information for this article was adapted from Daniels, Designing Great beers, pp 66 and John Palmer, How To Brew (3rd Ed.).
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