Cereals processing technology

Malting 195
Fig. 9.8 Fixed floor kilning vessel – fully loaded (photograph courtesy of Seeger
GmbH).
At the early (drying) stage of kilning, the heated air passes through the grain
bed, picking up moisture in the process, with the saturated air being exhausted to
atmosphere. After some hours of drying, when the moisture content of the grain
has decreased substantially from the initial 40 to 45 per cent, a start is made to
recirculate the air, initiating the curing stage of kilning. Progressively, the ‘airon’
temperature is increased, and the air volume reduced. A proportion of the
exhaust air is recirculated, and re-heated together with additional ambient air,
making up the required volume. This regime continues until the final moisture
content has been reached, typically four to five per cent. Initially the drying
temperature might be in the range of 60–65ºC, rising during curing to perhaps
65ºC for lager or other lightly kilned malts, to as high as 100–110ºC for
traditional ale malts.
During the initial drying stage of kilning, when saturated warm air is being
discharged, low grade heat can be recovered from the exhaust, to preheat
incoming ambient air. In recent developments, almost without exception, heat
recovery has been introduced through the medium of thousands of glass tubes
around 20 mm in diameter, arranged in bundles, in the shape of chevrons when
viewed from above. There are two fundamental concepts: in the first, the exhaust
air passes around the outside face of the glass tubes which are normally disposed