What is puck screen?
Puck screen is a metal mesh that can be made of stainless steel or other neutral materials that the don't affect the taste of coffee during the extraction. Puck screen can be compressed of multiple thin layers of mesh (like normcore 1.7mm stainless steel puck screen which is made of 4 compressed layers) or it can be a single thin mesh (like normcore 0.2mm titanium puck screen). Puck screens can be made in different dimensions for different portafilter types.
How to use puck screen?
Puck screens are used to extract espresso and they are meant to be placed over the coffee puck. It's better to pre-heat the puck screen before putting it over the coffee in the portafilter's basket. Puck screen must cover all the coffee surface to ensure a balanced extraction of coffee.
What do we have to use puck screen?
There are multiple advantages in using puck screen, but the main advantages are:
1st: puck screen can distribute the water over the coffee puck more evenly, so it helps for a more balanced extraction.
2nd: usually the coffee puck gets more fragile after a while of extraction so if you check the extraction pressure you can detect pressure decreasing through the rest of extraction, so it's more potential to have an unbalanced cup of espresso. By using a puck screen the coffee is pressing down over the extraction so there is no chance for water to get through the coffee bed easily (Channeling) and the extraction pressure will be more stable. So, puck screen helps us to have a more balanced espresso even in long extractions.
3rd: Puck screen helps your coffee machine to be cleaner and live longer, but how? When there's a puck screen above the coffee, most of the grounds can't go through the puck screen and they stick in its holes, so your machine's pipes and parts will be cleaner in long term and the taste of each coffee will be purer due to your clean pipes and as a result cleaner water supply.
NOTE:
Cleaning: it's important to keep your puck screen as clean as possible especially when you're using a thick model. For doing so, pour cold water and coffee detergent in a milk jug and place the puck screen in it. Use your coffee machine's steam wand to clean the puck screen thoroughly by heat, detergent and pressure.
Compatibility: Some espresso machines are using a screw at the middle of their shower screens. Before using a puck screen make sure to change the screw to a flat model so you will avoid damaging your puck screen.