What is tamping? 

Tamping is an important part of making espresso.  It involves using a tamper to apply even and consistent pressure to ground coffee in a filter basket. The goal of tamping is to form the ground coffee into a hard, evenly and densely packed pellet. This pellet is called the “puck.” When the hot water from the espresso machine hits the puck, the consistent density of the puck forces the water to evenly permeate it and properly extract the coffee.  If the ground coffee is not tamped or is loosely or unevenly tamped, the puck is likely to develop holes or loose spots as the water runs through it.  Recall that water will always select the path of least resistance.   Where holes and loose spots are evident, the water will run quickly through these sections.  The loosely packed sections of coffee will become over extracted because the majority of the water will run through this area only. The water will barely touch the more densely packed areas leaving them under extracted. Over extractions produce a bitter tasting shot while under extractions produce a thin, weak shot.

What is tamping pressure? 

Tamping pressure is the amount of pressure used to create the puck.  It appears relatively well established that 30 lbs. of pressure is the optimum amount of pressure to apply.  At 30 lbs., the puck is densely packed.   An evenly and densely packed puck helps provide for even extraction and optimum crema.

Why is tamping important? 

Besides providing for even extraction, tamping provides consistency.  In other words, it allows you to control one variable in the espresso making process.  When the tamping is consistent, variables such as minute grind changes are more easily identified.  Tamping increases your chances of consistently pulling great shots.

How do I tamp?