What happens if my coffee grind is too coarse?

When you brew coffee, you are essentially performing a chemical extraction. Hot water acts as a solvent, pulling sugars, acids, and bitter compounds from the grounds. When your grind is too coarse, the surface area of the coffee particles is limited relative to the volume of water flowing over them. This physical limitation leads directly to under-extraction, a state where the coffee is unable to contribute its full potential to your cup.

The result of this under-extraction is almost always characterized by a distinct sourness. While acidity is a desirable trait in many high-quality coffees, it should be balanced by sweetness and a pleasant, lingering finish. When under-extracted, that acidity becomes sharp, aggressive, and one-dimensional—often described as "salty" or "sour." The body of the coffee also suffers, feeling thin and watery rather than rich or textured.

This happens because different compounds extract at different rates during brewing. Acids, which are the most soluble, are the first to enter the water. Sugars and caramels take slightly longer to dissolve, and the heavier, bitter compounds—which provide depth when balanced correctly—are the last to be extracted. A coarse grind allows the water to finish its contact time before the sugars have had a chance to properly balance out those initial, sharp acids.

In practice, if your coffee tastes like "sour water," your first instinct should be to adjust your grind size. By moving toward a finer setting, you create more surface area for the water to work with, slowing down the flow rate and allowing the water more time to penetrate the particles. This change helps pull out those essential sugars, moving your brew from a thin, sour cup toward a balanced, flavorful experience. Always remember to change only one variable at a time when troubleshooting, starting with the grind.