La Marzocco strada ep Operating Manual - page 54
EN
54
A Few crucial facts you should understand
before operating the machine.
The STRADA is a powerful tool which acts
very differently, when compared with other
espresso machines.
Let’s consider all the main differences one
by one:
Temperature: the display of the STRADA
shows you a value that is an assumption
of the temperature of the water flowing
through the coffee puck.
However the thermocouple is placed in the
boiler (and not in the group), very close to
both the heating element and the water inlet.
This is the most volatile part of the boiler and
is both the coolest and hottest point.
Since the probe sits in the most inconsistent
spot, the CPU reacts faster and more
precisely depending on the temperature
changes, thus making the machine perform
more consistently.
Still the temperature at the group is estimated
by setting a default -3°C offset on the actual
probe reading. Therefore, if the operator
sets the temperature at 96°C, the display will
show 93°C.
Pressure: as with the temperature, the
displayed pressure on the STRADA is the
actual pressure on the coffee puck and
not the pressure at the pump, (as in ALL
other espresso machines). This explains
why the display shows low-pressure
readings when the group is flushed with
no portafilter or coffee packed in the
basket.
The coffee puck itself is making the
pressure build up, depending on its
permeability and resistance. This is
controlled by the operator through
adjustments in grinding, dosing and
tamping.
How the STRADA follows a defined
pressure profile: Each group of the
STRADA has a dedicated 24V DC gear
pump, which spins at a variable speed,
dispensing variable water flow-rate and
pressure.
The operator controls the pump’s speed/
pressure through a paddle that activates
a potentiometer, which sets the voltage
sent to the pump.
When the STRADA follows a set profile,
the CPU reads a pressure that is very
close to that in the coffee puck, therefore
it is very susceptible to minor changes in
grinding, dosing and tamping.
If, for instance, the operator tamps
slightly weaker, or packs in the basket a
smaller quantity of ground coffee, the
water will encounter less resistance in
its path, therefore the pump will have
to spin faster (consequently delivering
more water) in order to reach the set
pressure.
This will result in a totally different cup
of espresso.
In order to avoid this effect, it is crucial
to weigh/dose the ground coffee in
the basket accurately, and to calibrate
the tamping pressure, either by using
dynamometric tampers or tamping on a
scale.
Volume: Since, unlike many other
espresso machines, the STRADA delivers
the water to the coffee in a set time,
rather than a set volume, small changes
in grind, dose or tamp may result in
differing volumes by shot, though the
shot time will remain the same.
The STRADA Explained