Normally, the surface of the espresso pressed into the portafilter does not play a significant role: whether flat or convex, there is enough space between the coffee surface and the shower screen so that the water can be evenly distributed over the coffee and the powder can also penetrate evenly.
However, if flat sieves are used or significantly more than 7g (1 cup sieve) or 14g (2 cup sieve) are used, there may be too little space between the coffee powder and the shower sieve for optimal brewing water distribution. For this purpose, a Tamper Base Convex can be used so that a depression remains in the middle for optimal water distribution.
The lower part Joe Frex Base CONVEX can be combined with the handles: Joe Frex GALAXY/ EXCLUSIVE.