Because brewed coffee is 98.5% water, the chemical composition of your brew water is the ultimate solvent governor. Pure distilled or reverse osmosis water without added minerals yields flat, intensely sour, and hollow extractions.
1. Magnesium (Mg2+) vs. Calcium (Ca2+) Ions
Divalent cations bind to oxygen-rich flavor compounds in ground coffee. Magnesium ions (Mg2+) are small and possess a high charge density, making them exceptionally effective at pulling delicate fruit acids, floral esters, and oxygenated aromatics out of bean cellular matrices.
Calcium (Ca2+) also binds flavor molecules effectively but leans heavily towards extracting heavier, chalkier, and creamy compounds. A 3:1 Magnesium to Calcium ratio offers ideal flavor brightness.
2. Bicarbonate Buffer and pH Regulation
Bicarbonate (HCO3-) acts as a pH buffer. If alkalinity is too high (above 80 ppm), it neutralizes desirable organic acids, leaving the coffee tasting dull and chalky. If alkalinity is under 20 ppm, acidity becomes unpleasantly sharp and metallic.