Lesson 4 - Malting Process

Kilning is the final stage of malting, and the most energy intensive. It can take 24 to 48 h to achieve the required moisture level of 3-6%. 

The bed depth during malting is reduced from > 3 m in steeping, to around 1 m during germination, and then ideally to around 0.75 m during kilning. This reduces the differences between the malt produced in the bottom and top of the bed.

Green malt is kilned for the following reasons:

• To reduce moisture content, so that the malted barley can be safely transported and stored.
• To stop growth of the embryo at a point when the malt is well modified and will provide a high yield of starch and protein extract.
• To produce unique flavours and colours.
• To drive off dimethyl sulphide (DMS)
• To create a product that can be easily milled

Kilning is an energy intensive process; it typically consumes 75-85% of all energy in the malting process. Kilns use high air-on temperatures to evaporate moisture. The relative humidity of the incoming air is low, resulting in moisture moving from the kernel to the air. The flowrate of air through the grain is also much higher than that used during germination.

The grain moisture received in the kiln depends on the germination regime, but it is likely to be in the range of 43-46%. The grain is dried to a final moisture level between 3-6%. Any lower than this is a waste of energy and the malt produced can be too brittle. The longer that green malt is exposed to high temperatures, the more enzymes are lost. Some high enzyme malts have moistures around 8% for this reason. In kilning, the higher the grain moisture, the lower the air-on temperature used. High moisture combined with high temperature destroys enzymes.