Coffee Calculators

Water chemistry

Coffee Buffer & Acidity Calculator

KH is the water’s ability to neutralize acids. Brew TDS is how much coffee (including acids) actually dissolved. A high buffer index means the cup may taste flatter than the same coffee on softer water. This is a back-of-the-napkin ratio, not a pH meter.

Inputs

Units
ppm

Alkalinity as ppm CaCO₃ of the brew water.

%

Beverage TDS. Filter ~1.2–1.5%; espresso is much higher.

Results

Buffer index
0.30

KH relative to dissolved solids. Higher means more muting.

Acidity likely muted
No

Recommended gear

Calculation method

Buffer index divides KH ppm by brew TDS percent times 100, so 40 ppm against 1.35% TDS is about 0.30 — an SCA-ish starting water. The muted flag trips at 0.55 and above (about 75 ppm KH at the same TDS, the usual upper alkalinity band). Espresso TDS near 10% makes the same 40 ppm KH look small — shots are buffered by coffee, not by the water chart.

Exact formula

bufferIndex = khPpm / (brewTdsPercent × 100). ~0.30 at 40 ppm KH / 1.35% filter TDS. mutedAcidity if bufferIndex ≥ 0.55 (KH ≳ 75 ppm at that TDS). Limits: Acid profile, roast level and GH omitted; KH is not pH of the cup.

Roast still wins

A Vienna roast on 40 ppm KH will not taste like a washed Ethiopia. Water is a modifier, not a time machine for roast level.

Frequently asked questions

Should I lower KH to get more acidity?

Often, on filter. Too low and the cup goes sharp and the machine may suffer. Move 10 ppm at a time.

Why is espresso ‘not muted’ at 40 ppm?

Because 10% TDS dwarfs 40 ppm water alkalinity in this crude ratio. Shot acidity is more about roast and extraction yield than KH.

Is this pH?

No. pH needs a meter and a cooled sample. Buffer index is a KH-vs-strength sketch.

More in this topic

All tools in this topic