This tool estimates the pH of your mash before brew day so you can plan salt and acid additions to land in the ideal 5.2–5.4 range. It combines three drivers: the base acidity of the grain bill, the residual alkalinity of your water, and any lactic or phosphoric acid you add.
How it works
The estimate is built in three steps.
1. Base mash pH from grain color. With distilled water, darker malts mash more acidic. A common linear approximation is:
base_pH ≈ 5.66 − 0.025 × (grist color in SRM)So an all-pale grist (≈3 SRM) starts near pH 5.59, while a 20 SRM amber grist starts near 5.16 in distilled water.
2. Residual alkalinity shift. Alkaline water raises pH. Residual alkalinity in CaCO3 ppm is:
RA = (HCO3 / 1.22) − (Ca / 1.4 + Mg / 1.7)Each unit of RA shifts mash pH up; the shift also depends on how much grain you have buffering the water. The tool scales the RA effect by the water-to-grain ratio so big grists resist alkalinity more than thin ones.
3. Acid additions. Lactic and phosphoric acid lower pH. The tool applies approximate per-mL drop factors based on the total mash water volume.
The final estimate is base pH, plus the alkalinity shift, minus the acid drop.
Worked example
A pale ale: 10 lb of grist averaging 4 SRM, mashed with water at Ca 50, Mg 5, HCO3 100 ppm.
- Base pH = 5.66 − 0.025 × 4 = 5.56
- RA = (100 ÷ 1.22) − (50 ÷ 1.4 + 5 ÷ 1.7) = 81.9 − (35.7 + 2.9) = 43.3 ppm
- That positive RA nudges pH up toward ~5.7, above target.
- Adding about 2 mL of 88% lactic acid pulls it back down into the 5.3–5.4 band.
Tips and notes
- This is a planning estimate. Buffering varies by maltster, so always confirm with a calibrated pH meter 5–10 minutes into the mash.
- Measure mash pH at room temperature (cooled sample). Hot mash reads about 0.3 pH lower, which is why target ranges are quoted at 20–25 °C.
- Start from distilled/RO water if your tap water is highly alkaline — it is far easier to build a profile up than to neutralize a hard, alkaline source.
- For pale beers you almost always need to add acid; for dark beers the roasted malts may already pull pH down enough on their own.