5 things that help with remineralizing distilled or RO water to make better-tasting coffee

The most common failure mode in DIY remineralisation is mixing up a gallon of 'recipe water' and having to remix it from scratch each time. Two separate concentrates — one for hardness (magnesium), one for alkalinity (bicarbonate) — let you adjust each variable independently without redoing the maths every session. More importantly, they make it possible to dial in filter versus espresso profiles from the same stock: espresso tolerates higher alkalinity relative to hardness, filter benefits from the inverse. You cannot do that if you've pre-blended everything together. This is also why Lotus Water's separate-dropper approach got traction in specialty circles — independent control is genuinely useful, not a marketing feature.

Everyone says 'add magnesium for brightness.' Nobody mentions that magnesium sulphate — Epsom salt, the one in every recipe — carries two things into the cup: the magnesium cation, which does extract brightness and fruity acidity, and the sulphate anion, which introduces a dry, slightly bitter, almost stale-hop quality that compounds faster than you would expect. The ceiling on sulphate is surprisingly low. You can be using a perfectly sensible magnesium number and still be dosing enough sulphate to flatten the cup in a completely different direction from the problem you were trying to fix. If your remineralised water tastes dry or has a bitterness that sits in the wrong place, this is the first thing to check — not the total hardness.

The mistake is thinking of bicarbonate as something you add for 'balance.' What it actually does is chemically neutralise free hydrogen ions in the cup — it reacts with the organic acids that coffee extracts and converts them into non-acidic forms. At low doses this is useful buffering. Above roughly 60–70 ppm for light roasts you are not balancing acidity, you are deleting it. The bright citric and malic acids that make a good washed Ethiopian sing are precisely the compounds bicarbonate targets. The cup does not taste balanced; it tastes flat, muddled, and faintly alkaline. Dark roast drinkers sometimes prefer this without realising why. Light roast people just think the coffee is boring. The SCA target sits around 40 ppm as CaCO3 for a reason — that is the buffering zone, not the neutralisation zone.

Calcium chloride is sold in two common forms: anhydrous and dihydrate. Anhydrous is small white pellets; dihydrate is flakier and absorbs moisture more readily. The molecular weight difference means that if your recipe calls for anhydrous and you are using dihydrate, you need 36% more by mass to hit the same calcium concentration. Most cheap food-grade calcium chloride sold for cheese-making or canning on large online marketplaces is anhydrous; some water chemistry suppliers sell dihydrate; the bags are not always clearly labelled. If you have mixed a recipe that other people describe as tasting sweet and round, and yours tastes thin, this is one of the first things to check. Anhydrous also absorbs atmospheric moisture aggressively, so an open bag left in a humid kitchen gains mass over time and your doses quietly drift lower even when you weigh the same amount.

Most people evaluate a water recipe by brewing four separate pots over four mornings — which is expensive in coffee, introduces a dozen other variables between sessions, and takes a week to produce conclusions. Research into post-brew mineral addition shows that coffee tastes essentially the same whether minerals are added before or after brewing, which means you can evaluate multiple mineral combinations on a single brewed batch. Brew 900 ml with plain distilled water, split it into small cups, add your concentrates in different ratios to each cup, and taste them side by side in one sitting. The practical payoff is that you find your preferred profile in a single session rather than guessing across a week of mornings, and you can identify non-linear effects — profiles where both very low and very high alkalinity taste better than the middle range, for instance — that are easy to miss when you are comparing cups separated by days.