A Tamper is a tool used to flatten and pack powdered coffee into the portafilter of your espresso coffee maker.
Coffee Tamping ‒ the simple act of compacting the ground coffee into the portafilter so that it forms an even puck ‒ is a simple but crucial technique that you’ll need to learn. A puck is the tablet-shaped mass of compact coffee that is formed after tamping. Why is this important? If you don’t tamp properly with adequate force, then you leave holes and channels in the coffee puck. This allows water to take the path of least resistance and exit through the portafilter without actually extracting the oils in the coffee. If you tamp too hard, you might over extract, resulting in blacker coffee and poorer taste.