In order to be fermented by yeast, the food reserve of barley, starch must be converted by enzymes into simple sugars. Two enzymes, a- and b- amylases, carry out the conversion. The latter is present in barley – but the former is made only during germination of the grain.
Malting begins by immersing barley harvested at less than 12 percent moisture in water at 120 to 150C (550 + 600) for 40 to 50 hours. During this steeping period, the barley may be drained and given air rests, or the steep may be forcibly aerated. As the grain imbibes water, its volume increases by about 25 percent, and its moisture content reaches about 45 percents. A white roots heath, called a chit, breaks through the husk, and the chitted barley is then removed from the steep for germination.
Activated by water and oxygen, the root embryo of the barley corn secretes a plant hormone called gibberellic acid, which initiates the synthesis of a- amylase. The a- and b- amylases then convert the starch molecules of the corn into sugars that the embryo can use as food. Other enzymes, such as the proteases and b- glucanases, attack the cell wall around the starch grains, converting insoluble proteins and complex sugars (called glucans) into soluble amino acids and glucose.
Green malt is dried to remove most of the moisture, leaving 5 percent in lager and 2 percent in traditional ale malts. This process arrests enzyme activity but leaves 40 to 60 percent in an active state. Curing at higher temperatures promotes a reaction between amino acids and sugars to form melanoidins, which give both colour and flavour to malt.
In the first stage of kilning, a high flow of dry air at 500C (120F) for lager malt and 650C (1500F) for ale malt is maintained through a bed of green malt. This lowers the moisture content from 45 to 25 percent. A second stage of drying removes more firmly bound water, the temperature rising to 700 – 750 (1600 – 1700F) and the moisture content falling to 12 percent. In the final curing stage the temperature is raised to 750 – 900C (1700 – 1950F) for lager and 900 to 1050C for ale. The finished malt is then cooled and screened to remove root lets.
For efficient extraction with water, malt must be milled. Early milling processes used stones driven manually or by water or animal power, but modern brewing uses mechanically driven roller mills. The design of the mill and the gap between the rolls are important in obtaining the correct reduction in size of the malt. The object is to retain the husk relatively intact while breaking up the brittle modified starch into particles.
Mixing the Mash
The milled malt, called grist, is mixed with water, providing conditions in which starch, other molecules, and enzymes are dissolved and rapid enzyme action takes place. The solute-rich liquid produced in mashing is called the …