How to Prepare Coffee Brewing Water? How to Use Baking Soda and Magnesium Sulfate in Coffee? Why Can't Espresso Machines Use Tap Water?

The Role of Water in Coffee Brewing

In coffee making, colorless, tasteless water is the solvent! Extraction depends on it to carry the flavor compounds hidden inside the beans out into the cup. The deeper you go into brewing, the more you appreciate how much water matters.

You've probably seen the advice online: "don't use tap water for espresso." It's not that tap water is dirty — it's that it carries too many dissolved minerals. Boiled, they cling to kettle and boiler walls as scale, hurting both the machine's operation and the coffee's taste. And this matters well beyond espresso: for pour-over, your choice of water is just as critical. As FrontStreet Coffee often notes, different water sources carry different amounts of minerals. The right minerals help extract coffee's flavor compounds; too many get in the way, and the cup falls short. That's why brewing generally calls for soft water with a lower PPM.

Understanding Water Quality for Coffee

What counts as soft water? First, PPM: Parts Per Million, a concentration unit expressing the mass of solute per million parts of solution. Water quality is usually given in mg/L, and 1 ppm = 1 mg/L. The shorthand: more dissolved trace elements, higher PPM. Under the World Health Organization's "Guidelines for Drinking-Water Quality," water above 200 PPM is hard water, below 200 PPM is soft. Most city tap water sits under 200 PPM — technically soft — but coffee brewing draws the line more strictly! Above 140 PPM the water gets quite saturated, and it struggles to fully extract the coffee's compounds; even with every other parameter right, under- or over-extraction creeps in. That's why tap water isn't recommended for brewing coffee unless it's been properly filtered.

Optimizing Water for Coffee Brewing

The simplest fix is a filtration system on your tap. If you want to squeeze out even better flavors, you can build your own brewing water the way competition participants do. The easiest route — covered in a previous FrontStreet Coffee article — is a commercial water concentrate: mix one packet into an appropriate amount of pure water and stir. The only drawback is that it runs a little expensive.

There's also a more down-to-earth method, though it takes more work. You'll need: food-grade baking soda, food-grade Epsom salt (magnesium sulfate), and 3 bottles of 1L pure water (one-liter bottles make the math easy). Epsom salt can be hard to find offline, so order it online. The steps:

1. First, dissolve 1.68g of baking soda in one liter of pure water. This makes a 1000ppm solution — our prepared "buffer solution," or HCO3-. The buffer resists pH swings in the final water. Since it looks like plain water, label it and set it aside.
2. Next, dissolve 2.45g of Epsom salt in the second liter of pure water, stirring until it's fully dissolved. This "magnesium concentrate" carries the magnesium ions — about 1000ppm. Label it and set it aside too.
3. Finally, build the brewing water. We'll target the SCA's recommended range, with total hardness of 120-130ppm: add 40ml of buffer solution, 80ml of magnesium solution, and 880ml of deionized water. Your brewing water is ready.

The Impact on Coffee Flavor

FrontStreet Coffee brewed a pot of Ethiopian Kochere with both the prepared water and Nongfu Spring bottled water, and the difference was exactly what we expected — and significant. The Kochere brewed with Nongfu Spring showed bright lemon acidity, subtle white florals, and a black tea finish. The Kochere brewed with the prepared water had fuller, rounder acidity and more pronounced floral character!

So yes — waters genuinely differ! Don't underestimate this ubiquitous liquid: what it carries dissolved directly shapes the coffee you brew.

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FrontStreet Coffee Recommendation

Water this dialed-in deserves beans with delicate florals to show for it. FrontStreet Coffee's Yirgacheffe Guodingding — a washed lot from the Guodingding cooperative in Ethiopia — is the natural pick: the fruit is pulped before drying, which keeps its character clear and transparent, showing citrus and lemon tones with an elegant white-floral aroma, bright and refined in the cup.

For a slightly juicier expression of the same washed-Ethiopia style, FrontStreet Coffee's Kenya Cherry Tomato is a standout: SL28 and SL34 grown at 1550-1750 meters in Thika and washed with the local 72-hour double fermentation, it pours out cherry-tomato and dark-plum acidity with the fullness of fresh-pressed juice, layered with pear, black plum, and a long, clean finish of yellow sugar and green tea.