MALTING QUALITY TRAITS - Canadian Malting Barley Technical ...

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Chapter Four
In a special case, these three stages can take place in the same vessel (compartment). Besides the
multifunctional vessels/compartment designs, the arrangements of the vessels or compartments
also vary substantially from a horizontal arrangement in a conventional Saladin malthouse to the
vertical arrangement of modern malting towers. Therefore, the malting process will be reviewed in
generic and broad terms, rather than trying to focus on a particular type of malthouse.
Steeping
This very critical stage in the malting process takes place in a steep tank. The steeping process
initiates malting by providing water and oxygen to the resting embryo, thereby stimulating the
barley’s biological germination activity. At the same time, steeping causes hydration of the starchy
endosperm, facilitating its partial breakdown by hydrolytic enzymes (modification) during germination.
Additionally, the barley is washed, cleaning away materials that may hinder the malting
process or reduce the final malt quality.
The steeping stage usually consists of several alternately arranged “wet periods” and “dry periods”,
which are also called “immersion periods” and “air-rest periods”. In the wet period, barley is immersed
in water and in the dry period, water is drained from the barley. As the barley absorbs water
it begins to respire, taking up O 2 , releasing CO 2 and generating heat. In order to maintain optimal
growth conditions for the barley in the steep tank during the wet periods, an adequate amount of
air is delivered into the steep water, and during the dry periods, CO 2 is mechanically evacuated and
replaced with fresh air (oxygen). In steeping, the temperature of the barley is controlled between
12-20 °C, and the whole process may require up to two days (48 hours) in a modern malt plant.
The current understanding is that barley’s germination activity is activated when moisture levels in
the barley are elevated to 30 to 32% from an original level of 10 to 14%. However, these moisture
levels are not adequate for the barley to maintain target growth and to obtain the required degree
of modification in the following malting stages. In practice, barley moisture levels are increased to
42-46% for production of pale type malt, and 45-47% or higher for production of dark malt. For
economic reasons, maltsters always strive to use the shortest possible steeping duration to obtain the
target moisture level and chitting rate. At the start of each crop year, micro-malting and pilot-scale
trials are often undertaken to determine optimum steeping conditions. Water-sensitive barley, for
example, may require shorter immersion periods and longer air rests to ensure successful malting.
After the barley has obtained the target moisture level and is chitting evenly, then it is moved to
the next stage known as the “germination stage”.
Germination
In this stage, the steeped barley grains from the steep tank are transferred into a germination
vessel or a compartment to carry out the germination process. In some malthouses, steeped barley
is transferred into a pre-germination vessel to complete the first part of the germination and then
the barley is loaded into a germination vessel to carry out the remainder of the germination process.
‘Biological germination’ begins as early as at steep and is well established already when the germination
stage commences. The objectives of the germination are: to enable the barley to continue its
physiological activities started in the steep, to permit vegetative growth (acrospire and rootlet) in a
controlled manner, to develop hydrolytic enzymes, to break down cell wells, proteins and starches,
and to transform the steeped barley into “green malt”.
This stage usually takes up to four to five days, depending on the barley variety being processed
and the malt specifications expected. Cooled and humidified air is supplied to barley to provide O 2
for respiration, to maintain the barley moisture content , and to carry away CO 2 and heat (generated
by barley respiration). This creates an environment that controls the barley’s vegetative growth, whilst
encouraging the metabolic biochemical changes occurring within the barley kernels. A mechanical
turner passes through the grain bed at regular intervals (e.g. every eight to ten hours) to prevent
“matting” of the rootlets and compaction of the grain. Water sprays may be applied during turning
to replenish moisture which is inevitably lost along with heat and carbon dioxide during germination.
Temperature control is generally maintained in the range of 14 to 20°C, depending on progress
of modification and the type of malt being made. In general, higher temperatures and moisture