The HX Cooling Flush
After a heat exchanger machine, or HX machine as it’s commonly called has been sitting for a while the group is filled with superheated water. If you brew an espresso right now it will be overextracted and bitter and that’s where the cooling flush comes in, a technique used on almost all HX machines.
Let your machine warm up for a while so it’s at correct temperature. Now without the portafilter locked in, open the water flow and listen. Hear that hissing sound? That’s superheated water, or the flash boil as some call it. Let the water flow until it stops and a couple moments more, that’s a cooling flush. Right after a cooling flush a HX machine is sitting around 206-207F at the grouphead, that’s why we want to bleed a little more water after the flashboil ends to get the group down to around 203F for a proper espresso extraction.
Steps to better espresso with the cooling flush:
- Lock the empty portafilter into the machine.
- Listen for the flash boil to end and flush couple seconds more after it ends.
- Immidiately distribute and tamp the coffee that you already grinded, work fast as the machine will be up to temp again soon.
- Lock the portafilter in and pull your shot.
That’s it. The HX cooling flush is easy to work into your routine and will result in wastly better espresso.
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