MAINTENANCE MANUAL
Mirage technical manual
page 21 of 65
Adjust brew temperature
As mentioned in the previous paragraph, the coffee water temperature should not be set by changing
the steam boiler temperature. The temperature of the coffee water is a balance between steam boiler
water temperature, water circulation rate and heat loss, mainly through the group head. Since heat
loss is related to room temperature, draught, etc. it may be necessary to adjust the flow rate in the
thermo-siphon system. This is done by changing the aperture of the restrictor in the upper banjo.
Increasing the aperture of the restrictor has a bi-fold implication: (1) it increases the flow velocity of the
thermo-siphon system at idle which increases the group head temperature and thus brew
temperature, and (2) while brewing, the fraction of (hotter) water drawn from the top of the heat
exchanger increases w.r.t. the fraction of (cooler) water drawn from the bottom of the heat exchanger
which also increases the temperature of the brew.
If the machine is equipped with a fixed aperture restrictor (see Figure M 9a) you have to install a
restrictor with a different aperture. If your machine has adjustable restrictors (see Figure M 9b) you
can change the aperture by turning the knob on the restrictor-needle. Increasing the aperture of the
restrictor (turn knob counter-clockwise) will increase the brewing water temperature. Decreasing the
aperture (turning the knob clockwise) will decrease the brewing temperature (see Figure M 8).
The upper banjo can be reached by removing the cup warmer. When you change the restrictor in a
machine that is warm, it may take about 10 minutes for the temperature to re-stabilise. Several types
of restrictor-needle set-ups have been installed over the last few years. We therefore advise you to
use a temperature sensor installed in a filter holder to check the brewing temperature after
adjustments are made.
Figure M 8. Turn the adjuster-knob counter-clockwise to increase, and clockwise to decrease the brew
temperature
Notes!
Despite the fine thread on the adjustable restrictors, the system is quite sensitive. Turning the needle
1 full turn will result in a temperature change of 2-4 degrees Centigrade.
When the knob is not firmly mounted on the needle, you can use a screw driver to adjust the needle.
adjustable
restrictor needle
brew temperature
down
up
