A coffee grinder is a machine that grinds roasted coffee beans into powder for brewing, and grind quality is among the biggest determinants of cup quality. Burr grinders crush beans between abrasive surfaces to a uniform particle size, while cheap blade grinders chop unevenly, producing dust and boulders that brew inconsistently. Grind size must match the method: fine for espresso, medium for drip, coarse for French press. Grinding just before brewing preserves the volatile aromatics that dissipate within minutes of grinding. For anyone serious about coffee, a good grinder improves the cup more than any other single purchase.