Using a Puck Screen for Espresso

Question

What is the purpose of the puck screen when preparing espresso and does it need to be preheated?

Answer 1

Employing a puck screen when pulling an espresso shot ensures even penetration of the water into the coffee grounds which in turn enhances the quality of the espresso shot This type of screen is also advised to be pre heated prior to pulling the shot to avoid overheating or fluctuations in the temperature during the extraction.

Comments

A lifehack: instead of heating the puck screen with water, keep it on top of the group head. I have 2 pucks: one is on the group head, another (in a rubber stand) - on top of the machine. After I use the hot puck screen, another one moves from the cup warmer to the group head for the next time, and the used one, after washing, goes to the rubber stand. Constant rotating during the day.

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What is the reason for using the puck paper? Which type/brand?