Tamping is a critical and necessary step in the preparation of espresso coffee for a number of reasons. First it is important to explain a little about what in fact a tamp is. Tamps are available in many different sizes and shape, they are generally hand held, however some can be seen fitted to coffee grinders. They are commonly made of metal however some economy tamps are built out of plastic (commonly these are the ones packaged with home espresso machines). More information about styles of tamps can be found on my post: Types of Tamps
The purpose of a tamp is to evenly distribute the coffee in the filter basket of an espresso machine, as well as to compress the grinds. The art of brewing espresso is all about passing heated water through coffee to extract the oils of the coffee in the correct way. When the coffee is being brewed the water will always look for the path of least resistance on its way to your cup and your aim as the barista is to ensure that the water passes evenly through all of the coffee so that you maximise all of the beans you are using. Below is an example of what a correctly tamped filter should look like.
A correctly performed tamp will fulfill these main points:
- Distribute coffee evenly across basket
- This is that the coffee is at the same depth across the whole filter basket ensuring that there is not more coffee on one side than the other.
- Compress the coffee
- As the barista you can control how much pressure it applied when tamping, this can be varied to make minor adjustments to the pour time of your extraction.
- Eliminate any pockets of air or cracks in the coffee grinds
- this is again to ensure that there are no easy paths for the water to pass through.