the operation of a lever machine is neither difficult nor complicated contrary to some common prejudices.in fact in southern italy lever machines are predominant still today!
what makes the lever machine different from the pump machine is the pressure and extraction time profile.
the process of extraction on a lever machine starts with a pre-infusion under boiler pressure (ca. 1.2 bar) for ca. 6 seconds with the actual extraction following at an initial pressure of around 9 bar which drops to 0 bar towards the end of the extraction. the extraction time can be between 38 and 48 seconds. the temperature is lower than that of a pump machine.
to summarize, the contact time is longer, the temperature slightly lower, the pressure diminishing over the extraction time.
a pump machine has only a minimal pre-infusion, if at all, and starts the extraction process pretty much right away. the pressure of 9 bar is maintained over the course of the extraction time, usually around 30 seconds.
an exception is the La Marzocco Strada, which makes pressure profiling possible (the EP model rather than the MP).
in fact, experimenting with different profiles baristas often achieve the desired results with emulating the pressure profile of a lever machine.
the results for a particular coffee bean can be quite different on a pump machine in comparison to a lever machine. a lever machine is especially advantageous for single origin coffees.
No comments:
Post a Comment