i seem to get conflicting points of view on this. until recently, i had been under the impression that leaving the puck in the portafilter is the way to go in order to maintain the temperature on the group head. however, lately, i've been told by baristas that you want to keep them clean. i've heard very good baristas say to both things.
I don't worry about the puck as long as the machine is being backflushed on a regular. I am dedicated to cleaning our Marzocco and I have never had an issue with the screens (etc.) due to puck filth. People pulling shots with too much coffee in the basket will do more harm than an old, properly dosed, puck.
Your portafilter temp will remain consistent as long as you leave it in the group head. I train my baristas to ALWAYS keep your portafilters clean and clean immediately after each shot. This will improve in your timing drinks as well. Cleaning a portafilter before you have to make each shot becomes tedious and takes those few extra seconds that could be contributing to your customer service.
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