Malting consists in causing the grain to germinate and set in motion the transformation undergone naturally by the plant during its growth, and then halting that transformation more or less rapidly depending on the characteristics desired.
The transformation of barley (or wheat) into malt takes approximately eight days and can be broken down into four main stages:
This is the stage during which the grain is prepared for germination by causing it to take on moisture. Its moisture content is increased from 15% to 45%. At that point the grain is ready to germinate.
There are two main principles used: steeping by immersion or steeping by aspersion. In the first case, the grain is immersed in water, alternating with drainage and periods of exposure to air. During the immersion phase, the grain is turned and oxygenated using compressed air. During the drained phase, the air is renewed frequently to evacuate the CO2 and heat it produces and to provide it with the oxygen it needs. When aspersion is used, abundant spraying, coupled with ample renewal of the air, is used to humidify the grain.
This operation lasts 30 to 45 hours. At the end of the steeping process, the germ and the developing roots – called rootlets – appear.
The germ, activated during steeping, will develop during this stage, bringing about major biochemical changes inside the grain itself. The embryo will orchestrate the liberation and activation of a multitude of enzymes that will give the final malt a large part of its richness.
The layer of grain, spread out on a perforated grain floor, is continuously ventilated with air whose temperature and humidity are controlled, to allow the grain to respire – an indispensable activity at this stage. After three to six days, during which the grain is regularly turned and sometimes sprayed (or “watered”), the gemmule becomes as large as the grain itself and the rootlets that have developed look withered. At this stage the malt is referred to as green malt.
- This stage, often wrongly thought of as being simply a drying process, causes multiple transformations that make it in fact a true organoleptic and enzymatic refining process, indispensable to the production of quality malt. At first the biochemical reactions accelerate under the effect of the increasing temperature, but the decreasing humidity gradually halts all enzymatic activity. When the humidity level becomes low enough, the temperature is rapidly raised (to 85°C for a Pilsen or pale malt) during a curing period of a few hours whose purpose is to eliminate molecules that can cause unpleasant tastes and to bring out the desired aromatic compounds. The art of kilning thus lies in the choice of the recipe that will allow optimum control of these often complex reactions (the Maillard reaction, coloration, enzyme denaturing, elimination of off-flavors, etc.) Following a final cooling, the malt leaves the kiln with a humidity level of 4 to 4.5%, which will allow it to be properly stored for several months.
This is the finishing stage. The rootlets formed during germination are removed by passing the grain over vibrating screens. Since the grains are very dry, the rootlets detach easily. The high protein content of this "culm" makes it a desirable ingredient for making animal fodder.
When it leaves the malting plant, the malt is in the form of a dry and brittle golden-yellow meal. The malt is shipped in bulk by truck, barge, train, or ship, in bags and Big Bags, and in containers. Its shelf life can extend to up to a year if strict conditions regarding storage and hygiene are adhered to.