I've been experimenting with puck screens again...
A few years ago when it was first in vogue to use puck screens and paper filters for espresso extraction, I spent a bit of time trying these techniques out. In the end I decided that there wasn't a significant improvement in espresso in the cup and relegated them to the back of the coffee equipment drawer.
For those of you new to these items, a puck screen is a thin metal mesh insert (as pictured at the top of this newsletter) which is placed on top of the tamped bed of coffee grounds in your portafilter. Paper filters can also be placed in the portafilter basket prior to grinding coffee into the basket. The main benefits of these items are purported to be that puck screens result in more even extraction because they smooth out the delivery of water from the group head when you turn the pump on (or push a lever or allow a spring to push a lever!), and that paper filters effectively reduce resistance at the bottom of the puck allowing for finer grinding of coffee and higher extraction yields without risking channeling of water through the coffee puck.
Recently, Lance Hedrick has provided some extraction yield data on puck screens and paper filters. He suggests that the use of a puck screen by itself (without paper filter) consistently increases extraction yield within a tight statistical range. I am not in the camp that thinks that extraction yield itself is the be all and end all metric for determining the quality of espresso in the cup, however these findings were interesting enough for me to pull the puck screen out again and have another go.
My trials were anything but scientific (ironic I know given that I approach roasting in a highly scientific manner)... I tasted the difference between extractions with and without a puck screen and I do think that there is a difference. I also asked my wife to taste the two cups (on multiple occasions) and she found consistent differences as well.
Before giving away the (highly unscientific) results I wanted to clarify that I have both equipment and daily process which likely lead to very high extraction efficiency. My machine has a needle valve and a secondary water circuit to allow for low pressure pre-infusion (I have this set at 2 bar currently) followed by standard 9 bar extraction. I have installed a Pesado shower screen in the group head which is specifically designed for even water distribution (I'll write a newsletter article about this separately). I am meticulous in terms of puck preparation... I use a small whisk for even distribution, I have a fitted tamper for each of the various portafilter sizes which I use, and I'm lucky enough to use a great coffee grinder, a KafaTek Monolith Flat.
Given all of the above, we have found it pretty amazing to experience an uplift in espresso quality when using the puck screen. We've found our espresso to have more distinct flavour characteristics, greater clarity and beautiful balancing brightness. Using a puck screen each morning has become part of the standard process. I'll include a photograph of an extracted puck having used a puck screen and you'll clearly see how even the surface is!
To learn about filtering espresso click here
To read about new green bean arrivals click here