The term grooming is often used to describe the manual adjustments made to coffee grounds in the basket after the beans have went through the grinder, and before being inserted into the group head.
The concept of coffee grooming comes from the logic that spreading the grounds evenly in the basket would aid a more even flow of water, and result in a more even espresso.
The argument against this is that once the extract is collected in the demitasse, they blend together and become even. So grooming is more of an act to make baristas look like they really care about the coffee.
Whatever the case, my intuition says that groomed coffee grounds in the basket allows the portafilter to get a better fit into the group head.
Thus, enabling the espresso machine to perfectly do what it’s supposed to do. This would be an important factor in consistent brewing.
Common methods of grooming include tapping the basket to spread out the grounds, using of the index finger and thumb to even them out, or use tools that are specifically manufactured to do this job.
We use one such tool at the cafe which is disc shaped with “blades” at the bottom. Place the tool on the basket, and with one quick spin, the grounds would be perfectly evened out and flat.
It saves a lot of time when compared to using your hands, looks more professional, keeps your hands clean, and you can achieve a perfect balance every time.