Everyone obsesses over the beans and the ratio, but the part that makes or breaks your cold brew is the grind size. You'd be surprised how many counter conversations start with "Why is my cold brew bitter?" and the answer is always the same: grind too fine.

When you steep coffee in cold water, extraction happens slowly. Fine grounds release too much too fast, and you get harsh, over-extracted flavors. Coarse grounds release gently, leaving you with a smooth, sweet concentrate.

A quick test: pinch your grounds. They should feel like rough sand, not powder. If you're using a blade grinder, pulse in short bursts to avoid turning half your beans to dust. Even a cheap burr grinder is a huge upgrade if you're serious about cold brew.