Water
A cup of filter coffee is more than 98% water, and the argument stops where it becomes interesting: perfectly drinkable water can give a flat or bad coffee, because it is not its defects that matter but its ions. The physics of dissolution, alkalinity and hardness, units, salts and their hydrates, making a concentrate, published recipes, measurement, and a taste-profile calculator in the manner of commercial mineral concentrates. After the “Water” chapter of Gagné (2021), his 2018 articles, Colonna-Dashwood and Hendon (2015), the SCA and the Zurich laboratory.
The 13 sections of this plate
Each section has its own page. The first sentence says what you will find there.
- 01What water does, and whyTo understand why water extracts coffee, we have to spend a minute on its shape.
- 02Alkalinity and hardness, and the words that misleadTotal alkalinity is the capacity of water to resist changes in pH.
- 03UnitsIons are measured as mass per volume, mg/L, often written ppm on American bottles, which Gagné considers misleading since it is not a number of ions per million molecules.
- 04The standard, and the zones that do not coincideOn a graph of hardness against alkalinity, the tap waters of big cities line up along a diagonal where the two are equal, because water takes its minerals by dissolving limestone; filter pitchers shift the composition along that same line, toward zero.
- 05Salts, and the hydrate trapThe minerals historically used are calcium chloride, magnesium sulfate, magnesium chloride, sodium bicarbonate and potassium bicarbonate; calcium carbonate, calcium sulfate and calcium citrate exist but are harder to find or to dissolve, the citrate acting on alkalinity through an anion different from bicarbonate.
- 06Getting pure waterThis is often the hardest part, and the least ecological.
- 07Making a concentrateAdding the salts directly to each liter demands extreme precision and a lot of agitation.
- 08Published recipesGagné tried only three of them and usually prefers the simplified Rao/Perger, which he could not tell apart in a blind tasting from the full Rao/Perger, easier to prepare and more convenient.
- 09The profile calculatorChoose a taste profile, or set your own targets; say which water you start from; set the strength.
- 10Measuring your waterConductivity meters, called TDS meters, measure the electrical conductivity of water and translate it into total dissolved solids.
- 11Water in machinesAn espresso machine or a boiler coffee maker heats water continuously, and therefore concentrates scale.
- 12Before chemistry: water in the old treatisesThe oldest advice Ukers reports comes from a 17th-century London merchant: some make coffee with spring water, but it is not as good as river water or…
- 13TodaySince 2018, coffee water has become a product that is bought.
Elsewhere on the site, the passages that deal with the same things as this page. Computed from the text, not picked by hand.