Water chemistry

Three numbers come off your water report before any salt goes in, and then a solver does the rest. The water guide is the walk through the panel; this page is what the panel is computing.

Residual alkalinity

Residual alkalinity is Kolbach’s, from 1953, and still the most useful single figure about a brewing water. Alkalinity pushes mash pH up. Calcium and magnesium push it down, but not equally, and Kolbach’s divisors are the measured ratio of how much. A negative residual alkalinity means your water will drop a pale mash into range on its own. Dublin’s is about 175 and Pilsen’s about 6, which is most of the reason those two cities brew what they brew.

Sulfate to chloride

The ratio is the balance number, and we do not quote it when it cannot be calculated. A blank ion on a report means the report does not say, which is a different fact from zero. And a water with under about fifty parts per million of both has too little of either to carry a flavor whatever they divide to, so the ratio is withheld there too.

The salt solver

Given your water, a target and how much you are mashing and sparging with, the solver searches every combination of up to three of the salts you stock, scores each on how far each ion lands from target in units of that ion’s own tolerance, and hands back the best. Doses are rounded to what a brewing scale can read, and the fit reported is the fit of the rounded doses rather than the ideal ones, because the rounded ones are what you are going to weigh.

The beer these numbers come from

Reference pale ale — 20 L into the fermenter, a 60 minute boil.

Grist	Amount	Color
Crisp Maris Otter Pale Ale Malt	4.5 kg	2.8 °L
Thomas Fawcett Caramalt	0.35 kg	9.9 °L

Hops	Amount	Alpha	Addition
Magnum	15 g	13.5 %	60 min boil
Cascade	30 g	6.8 %	10 min boil
Citra	40 g	13 %	20 min stand at 80 °C

It comes out at
Original gravity	1.0507
Final gravity	1.0094
Alcohol	5.52 %
Bitterness	35.66 IBU
Color	5.14 SRM (10.12 EBC)
Into the fermenter	20 L

The numbers

Residual alkalinity

-37.06 ppm as CaCO₃, from kolbach-1953.

RA = Alk − Ca hardness / 3.5 − Mg hardness / 7  (all as CaCO₃)
⇒ Residual alkalinity = -37.06 ppm as CaCO₃

Input	Value	Unit
Alkalinity	77.9	ppm as CaCO₃
Bicarbonate	95	ppm
Calcium	153.7	ppm
Calcium hardness	383.9	ppm
Magnesium	9	ppm
Magnesium hardness	37.1	ppm

What it assumes:

• In elemental ppm the same formula is RA = Alk − Ca/1.4 − Mg/1.7.
• -0.74 mEq/L.

Sources:

• Der Einfluss des Brauwassers auf den pH-Wert der Würze und des Bieres, Monatsschrift für Brauerei 6 — Paul Kolbach, 1953
• Water: A Comprehensive Guide for Brewers — John Palmer & Colin Kaminski, Brewers Publications, 2013

Sulfate : chloride ratio

1.94 ratio, from sulfate-chloride-ratio.

ratio = SO₄ ppm / Cl ppm
⇒ Sulfate : chloride ratio = 1.94 ratio

Input	Value	Unit
Sulfate	117.1	ppm
Chloride	60.5	ppm
Balance	balanced	—

What it assumes:

• Balanced

Sources:

• Water: A Comprehensive Guide for Brewers — John Palmer & Colin Kaminski, Brewers Publications, 2013

Water profile fit

1.96 weighted RMS tolerances, from nnls-subset-enumeration.

minimize ‖W(Ax − b)‖² subject to x ≥ 0, ‖x‖₀ ≤ maxSalts
⇒ Water profile fit = 1.96 weighted RMS tolerances

Input	Value	Unit
Max salts	3	—
Salts used	2	—
Allowed salts	gypsum, calcium-chloride-dihydrate, epsom-salt, table-salt, magnesium-chloride, baking-soda	—
Total water	30	L
Fitted water	30	L
Dilution fraction	0	—
Split strategy	proportional	—
Dose rounding	0.1	g
Largest ion error	95	ppm
Salt combinations tried	15	—

What it assumes:

• Score is the RMS of (achieved − target) / tolerance across the six ions: 0 is exact, 1 means “off by one tolerance on average”.
• Doses are rounded to 0.1 g and the fit reported here is the fit of the rounded doses, not of the ideal ones.

Sources:

• Solving Least Squares Problems — Charles L. Lawson & Richard J. Hanson, 1974
• Water: A Comprehensive Guide for Brewers — John Palmer & Colin Kaminski, Brewers Publications, 2013