Is it better to grind coffee by weight or volume?

The preference for weight over volume is not merely a matter of precision; it is a necessity dictated by the physical properties of the coffee bean. Coffee is a biological product, and its density is determined by its growth environment—specifically altitude—and the chemical changes induced by roasting. High-altitude, 'strictly hard' beans are physically denser than those grown at lower elevations. Furthermore, as a bean roasts, it loses mass through dehydration and organic degradation while its volume remains relatively stable, causing its density to drop significantly. When you measure by volume, you are essentially guessing at the amount of soluble material available for extraction. A scoop of a light-roast, high-density bean will weigh substantially more than a scoop of a dark-roast, low-density bean. This discrepancy leads to inconsistent brew strengths and unpredictable extraction yields. For the producer, this variability is a hallmark of terroir and processing; for the brewer, it is a variable that must be neutralized. By using a scale, you bypass the inconsistencies of bean size, shape, and roast-induced expansion, ensuring that the ratio of coffee to water remains constant. This shift from volumetric 'scoop' culture to gravimetric precision is the single most effective way to improve brew consistency, as it allows for the accurate replication of recipes regardless of the specific coffee being used.