Mash pH Calculator from Water and Grain Bill

Mash pH depends on the grist's own acidity and on the water's residual alkalinity, more so in a thin mash. 4.5 kg of pale malt and 0.3 kg of 60 °L crystal in 15 L of water with 50 ppm of alkalinity and 50 ppm of calcium land near pH 5.6, within the 5.3–5.7 range generally considered adequate.

How mash pH is estimated

This calculator uses the model Kai Troester proposed from his mash experiments. First, the grist’s pH with distilled water: the base malts contribute their own distilled water mash pH, and the specialty malts lower it with their acidity:

\begin{aligned} pH_{DI} = {} & \sum pH_b\,g_b + 5.7 \sum g_s \\ & - \frac{0.14 \sum a_s\,g_s}{R} \end{aligned}

where $g$ is each malt’s share of the grist, $pH_b$ a base malt’s distilled water mash pH, $a_s$ a specialty malt’s acidity in mEq/kg and $R$ the mash thickness in L/kg. Crystal malts are counted at $14 + 0.13 \times$ their color in EBC and roasted malts at about 40 mEq/kg.

The water then shifts the pH in proportion to its residual alkalinity, more so in a thin mash:

pH = pH_{DI} + (0.013\,R + 0.013) \times RA

with $RA$ in mEq/L, after Kolbach.

For example, 4.5 kg of pale base malt (distilled water pH 5.7) and 0.3 kg of 60 °L crystal malt in 15 L of water give a distilled water pH of about 5.60. With water at 50 ppm of alkalinity, 50 ppm of calcium and 5 ppm of magnesium, the estimate is 5.62.

Inside Foambyte, water profiles and each recipe’s water settings keep your source water and salt additions.

Reference table

Estimated mash pH of a grist with a distilled water mash pH of 5.70, by mash thickness (rows, L/kg) and residual alkalinity of the water (columns, ppm as CaCO₃)
L/kg \ RA	-100	-50	0	50	100	150
2.0 L/kg	5.62	5.66	5.70	5.74	5.78	5.82
2.5 L/kg	5.61	5.65	5.70	5.75	5.79	5.84
3.0 L/kg	5.60	5.65	5.70	5.75	5.80	5.86
3.5 L/kg	5.58	5.64	5.70	5.76	5.82	5.88
4.0 L/kg	5.57	5.64	5.70	5.76	5.83	5.89
5.0 L/kg	5.54	5.62	5.70	5.78	5.86	5.93

Sources

Kai Troester. “The effect of brewing water and grist composition on the pH of the mash”, braukaiser.com, 2009. Mash pH model: distilled water mash pH of the grist, specialty malt acidity (crystal malts 14 + 0.13 per EBC, roasted about 40 mEq/kg, titrated to pH 5.7), the 0.14 acidity factor and the mash-thickness slope 0.013·R + 0.013. The paper is licensed CC BY-NC 3.0; only its equations and coefficients are used here, none of its text, tables or figures.

Frequently asked questions

What mash pH should I aim for?

A mash pH of about 5.3 to 5.7, measured at room temperature, is generally considered adequate for brewing. Many brewers aim near the middle of that range.

How accurate is the estimate?

Treat it as a starting point within about 0.1 to 0.2 pH. The model comes from small, finely ground test mashes, and malts vary: base malts of similar color can differ noticeably in their distilled water pH. Measure your mash with a calibrated pH meter and adjust.

What is the distilled water mash pH of a malt?

The pH a mash of that malt reaches with distilled water. It describes the malt's own acidity. Pale base malts are usually around 5.7; more highly kilned malts like Munich tend to be lower. If your maltster lists it, enter that value.

How do I lower my mash pH?

Add calcium (gypsum or calcium chloride), reduce the water's alkalinity, add acidulated malt, or use a food-grade acid such as lactic acid. The model behind this calculator was fitted on base, crystal and roasted malts, so it does not cover acidulated malt or acid additions: add a little at a time and measure.

Why does mash thickness matter?

A thinner mash has more water per kilogram of grain, so the water's alkalinity has more effect on the pH. In Troester's measurements, the pH change per unit of residual alkalinity rose steadily with mash thickness.