Malting serves the purpose of converting insoluble starch to soluble starch, reducing complex proteins, generating nutrients for yeast development, the development of enzymes, and the achievement of a distinctive character by color and aroma compounds. High extract yield and low malting loss are economic goals. The process of malting involves three main steps. The first step is soaking the barley, also known as steeping; next, the grain is allowed to germinate and sprout; and finally, heating or kilning the barley produces its final color and flavor.
The purpose of steeping is to evenly hydrate the endosperm mass followed by an air rest period that allows the water content of the grain to increase. The absorbed water activates naturally existing enzymes and stimulates the grain to develop new enzymes. The water temperature and aeration are vital for producing high-quality malt. Steeping begins by mixing the barley kernels with water to raise the moisture level and activate the metabolic processes of the dormant kernel.
In the next step, the wet barley is germinated by maintaining it at a suitable temperature and humidity level until adequate modification has been achieved. From the outside of the grain, rootlets emerge from the kernel, and within the outer husk a shoot—or acrospire—grows. Modification is the breakdown of protein and carbohydrates and results in the opening up of the seeds’ starch reserves. This process typically takes 4 to 6 days and results in what is called “Green Malt.”
At an appropriate point the germination process is arrested by application of heat, termed kilning. This stabilizes the green malt such that relevant enzymes and reserve materials are available for subsequent extraction and further degradation to release fermentable sugars during wort production. The temperature regime in the kiln determines the color of the malt and the number of enzymes which survive for use in the mashing process. For example, low temperature kilning is more appropriate for malts when it is essential to preserve enzymatic (diastatic) power. These malts are high in extract but low in coloring and flavoring compounds. Pilsner and pale ale malts are examples of malts kilned at low temperatures.
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