Brewing Unit - Bosch TCA640 Series Repair Instruction

4.3

Brewing unit

The brewing unit forms the central element in the espresso machine.
The brewing unit extracts the aroma, flavour and bitter agents from the
ground coffee and forms the crema.
4.3.1 Operating principle
1 Control lever, filling amount
2 Filling shaft
3 Locking lever
4 Water inlet
5 Clutch, drive shaft
58300000120060_ARA_en_c.doc – 18.09.09
6 Catch
7 Discharge chute
8 Stripping handle
9 Brewing head
10 Coffee outlet
Ground coffee pours through the filling shaft (2) into the brewing
chamber and is compressed. Hot water is introduced under pressure
via the water supply (4) and forced through the ground coffee. The
coffee which is produced is conveyed to the coffee outlet (10). To
optimise crema formation, the crema valve, which is situated above
the brewing head, opens when the pressure reaches 4.5 bar.
At the end of the brewing process the used coffee dregs are emptied
into the dregs drawer via the discharge chute (7).
4.3.1.1 Variable brewing chamber
The brewing unit consists primarily of the brewing chamber (A), into
which the ground coffee (7 g – 14 g) is metered, and the spring-
mounted brewing head (B) which moves upwards to seal the brewing
chamber.
The ground coffee is compacted and compressed in the brewing
chamber. When hot water is pumped into the brewing chamber, the
rising water pressure pushes up the brewing head, increasing the
volume in the brewing chamber. This improves extraction of the
flavours and formation of the crema.
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