Normally, the surface of the espresso pressed into the portafilter does not play a significant role: whether Flat (flat) or Convex (convex), there is enough space between the espresso surface and the shower sieve so that the water can distribute itself evenly over the espresso and the powder also penetrates evenly. However, if flat sieves are used, or if significantly more than 7g (1-cup sieve) or 14g (2-cup sieve) is used, there may be too little space between the espresso powder and the shower sieve for optimal brewing water distribution. For this purpose, a Tamper Base Convex can be used to leave a trough in the center for optimal water distribution.
Please LEAVE the rubber washer supplied with the TECHNIC, POP and CLASSIC handles! For ELEGANCE handles, REMOVE the rubber washer!