When we say ‘puck preparation’, we are talking about everything that happens from the moment the coffee exits the grinder to the moment the portafilter is inserted into the machine. This stage of espresso making is the part where the manual skill of the barista has the greatest effect, and can easily make the difference between a mediocre coffee and an outstanding one. Good design and automation have helped to eliminate many of the variables in espresso making, including those around tamping, but the other stages of puck preparation are still very much in our hands as baristas, and so they are worth paying close attention to.
Good puck preparation means the coffee will be extracted as evenly as possible, making the coffee taste sweeter and more transparent, and also allows higher extractions before over-extraction flavours become apparent, meaning we can use less coffee to get the same (or better) results.
What Defines Good Puck Preparation?
A spent puck
The ideal puck has the following characteristics:
Coffee is evenly distributed throughout the puck. This means the puck should have the same density across the whole puck and also from top to bottom. It also means that other features of the puck, such as the particle size distribution and the permeability to water, should be equal throughout the puck.
It has an appropriate void fraction. In other words, the size and distribution of the gaps between the coffee particles are important, not just the particles themselves. The voids between particles determine the flow of water through the puck, and this has numerous effects, from determining shot time to altering the relative extraction of larger molecular weight compounds such as tannins. Small changes to void size can have dramatic effects on flow. We will discuss this in more detail in Chapter Four, entitled ‘Compaction and Permeability’.
It is not liable to disruption from the flow of water.