It’s one of the most important parts of your espresso machine. It’s also the one of the simplest, cheapest, hardest working and probably the most mistreated. I’m referring to the Collar Seal, also known as the Group Seal or Group Gasket. They cost about the same as a regular burger meal, yet if the collar seal fails to work exactly as designed, the shot is immediately wasted and it’s back to square one.
The role of the collar seal is to create a seal between the top of the portafilter basket and the surface of the group head that surrounds the water dispersion point. This ensures that when the brew pump is running and the brew valve is open, all of the heated water has no choice except to travel through the ground coffee and into the portafilter basket, therefore producing our shot.
This all sounds simple enough except for the fact that the water is heated to within 5 degrees of boiling and the pressure it is holding back is 130 pound per square inch (psi). To give you some perspective, 130 psi is about the same pressure you would experience if you were scuba diving at a depth of 300ft, which also turns out to be the crush depth of a ping pong ball. For this reason you should never place a ping pong ball inside your portafilter handle while brewing a shot of coffee…
So how can we help this simple, yet critical ring of rubber do its job for many months without leaking.
1. Ensure the rim of your portafilter basket is totally free of loose coffee grinds before inserting it into the Group. The coffee particles will be pressed into the relatively soft rubber of the seal causing a leak and over time, permanently deform it. This can be achieved by simply wiping your flattened hand across the top of the basket.
2. Do not allow your baskets to become damaged while knocking out the puck. Dents and crack on the rim of your basket will prevent a good seal.
3. Allow the portafilter handles to rest lightly in the group while not being used. Having the handle in tight for long periods such as overnight causes the seal to compress and harden prematurely.
4. Clean the seals thoroughly at the end of the day with the tip of a cloth or a brush designed for the purpose.
Every one of your humble collar seals will easily last several months if make the small amount of effort required to keep them in top shape. If you do, the only indication you will have that they are getting a bit old will be that your handles are going around too far during use. Then, as your tech throws them in the bin, pat yourself on the back before turning back to the grinder and the lunch time rush.