Tamping

Tamping is the process of compacting material by pressing, striking, or vibrating it to reduce voids and improve stability. The term is used in several fields, most notably espresso preparation and civil or railway engineering, where the goal is a uniform, stable surface or layer.

In espresso preparation, tamping involves compressing a measured dose of finely ground coffee in the portafilter. A smooth, even puck supports uniform water flow during extraction. Tools include a coffee tamper (flat or convex bottom) and applications such as distribution tools or levelers. The technique typically requires a firm, even pressure perpendicular to the coffee surface and a final wipe of the rim to prevent channeling. Common guidance places the applied force in a range around 9 to 15 kilograms (roughly 20 to 35 pounds), though practices vary by tradition and equipment. Key factors for a good tamp include consistent grind size, correct dose, even contact across the puck, and avoiding tilting or uneven pressure. Poor tamping can lead to uneven extraction, channeling, and inconsistent flavor.

In civil and railway contexts, tamping refers to mechanically compacting ballast or soil. Tamping machines or hand tampers strike the ballast around sleepers to settle it, relevel the track, and restore geometry after disturbances. Proper tamping improves bearing capacity and stability, drainage, and ride quality. However, over-tamping or under-tamping can cause distortions, excessive settlement, or damage, necessitating further adjustments or realignment.

Tamping is a general term for shaping and stabilizing loose material through controlled compaction, with specific methods tailored to the material and purpose.