Cereals processing technology

Malting 193
Fig. 9.7 Fixed floor germinating vessel – loading in progress (photograph courtesy of
Seeger GmbH).
During germination, the Maltster’s requirement is to provide an adequate
supply of high humidity air at the desired temperature, the volume and velocity of
the fan being designed to maintain as little temperature differential through the
bed as is practicable, linked with the need to minimise the loss of moisture by
evaporation through the depth of the bed. Ideally, depending on the barley variety
and the type of malt to be produced, the temperature should be maintained in a
range of about 12 to 16ºC, or 15 to 19ºC. To achieve these targets, the depth of
grain bed must be restricted, and a normal design figure would be to adopt a
loading on the floor of about 550 to 600 kg/m 2 of original barley. For example, in
the case of a 300 t batch of original barley, the area of the germinating vessel floor
might therefore be approximately 500 to 545 m 2 , or about 26 m in diameter. This
would give a depth of steeped barley, after loading, of about 1.2 m. Increasing the
depth of the bed not only makes the control of humidity and temperature more
difficult, but also increases electrical energy costs for the fan.
The residence time for the barley in the germinating vessel can vary
considerably, depending on such factors as the variety of barley, the growth
which has taken place in the steep, the method of filling the vessel, temperature,
humidity, type of malt required, and additives used, but normally the duration
would be in the order of four to five days. Ideally, five germinating vessels
would be provided.
Where the plenum has adequate headroom, manual cleaning can be readily
executed, although automatic underfloor washing is offered by manufacturers. It is
also possible, where a rotating turner unit is incorporated (with a fixed floor) to