The Perfect Espresso; Functional Principle; Warming The Cups - Bosch TCA640 Series Repair Instruction

5.2

The perfect espresso

A genuine espresso is prepared according to a specific extraction
process in which the water is forced under high pressure through
finely ground coffee in order to release all the flavours.
The excellent quality of the result in the cup depends on the
selection and composition of the raw coffee from different countries
of origin, the degree of roasting, the fineness of the grinding and the
extraction method: Applied pressure, water temperature and
extraction duration.
A perfect espresso can be identified by its distinctive taste, intensive
flavours and a dense body, refined by a crema of perfect consis-
tency.
5.3

Functional principle

Water and coffee beans are held in the supply containers ready for
the preparation of coffee. After the product has been selected, the
coffee grinder starts to grind the beans. Ground coffee is dosed into
the brewing unit. The grinder stops after the time assigned to the
volume. The brewing process starts with the movement of the brewing
unit to the upper end position. When this is reached, the water pump
starts to supply water. Water is sucked out of the water tank through
the flow meter. The flow of water sets the impeller in motion, which
generates electrical pulses. The run time of the pump is determined by
the number of pulses. The pump conveys the water through the
heater at a pressure of 5 - 8 bar. Depending on the product selected
(coffee, hot water or steam), the water is heated to a temperature of
between 86 °C and 130 °C. For dispensing coffee, the system is
closed, the pressure can increase to over 4 bar, the outlet valve opens
and water flows through the drainage valve into the brewing unit.
58300000120060_ARA_en_c.doc – 18.09.09
For steam or hot water dispensing, the solenoid valve opens the
system. Hot water or steam flows out of the steam nozzle. The
pressure in the system remains low and the outlet valve remains
closed.
The functions are monitored by sensors and microswitches via the
logic printed board assembly. All units, such as motors, pumps,
heating element and solenoid valve are supplied with power via the
power printed board assembly.
5.4

Warming the cups

The warm exhaust air from the coffee heater is used to warm the
cups. The air rises and flows through openings in the cup rack. There
is no active heating element for warming the cups.
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