Malting is the art of naturally developing enzymes within the kernel of a cereal grain, like barley, and then quickly halting the growth process. Why is malting necessary? Well, raw grain lacks the natural enzymes necessary to convert starches to sugar, which is necessary for certain uses of the grain such as brewing beer.
After harvest, barley kernels start out with a densely packed matrix of high molecular weight starch granules, known as the endosperm. In the normal life process, if the kernel were planted in the ground and provided enough water, the embryo at the end of the kernel would signal growth and release enzymes that begin to break down the starchy endosperm. The starch is then converted to simple sugars that the plant uses as food in order to sprout roots, develop a stem, and grow.
In malting, we desire the same start of this natural life process whereby the enzymes necessary to break down the starch are fully developed. However, if the kernel's growth were not halted then all of the simple sugars that were converted from starch would be consumed by the plant. That would leave nothing left for a brewer to "extract" in order to make sugary wort.
Therefore, maltsters allow the development of the plant to a certain desirable point, where all the enzymes necessary to convert starch to simple sugars are developed, and then we halt the growth process by quickly drying the kernel. At the drying stage the nearly finished malt can be kilned, "stewed", roasted, smoked, or finished in a number of ways to produce an endless variety of possible malts, each with a different flavor profile.
The three steps of malting are actually quite simple: steeping (water), germination (time), and kilning (fire).
We start by steeping raw grain in water to allow the embryo to soak in moisture. At around 30% moisture content the embryo is sufficiently pleased with the water availability and triggers the growth process as the kernel continues to take in water.
The next step of germination is giving the kernel time to develop the natural enzymes for starch conversion and protein degradation. Also during this stage the "green malt" sprouts small rootlets that must be removed after drying. While it sounds simple, germination is the most important step of the malting process. Without proper enzyme development we would have a starchy food source with no tools to break it in to edible sugars!
Finally, to prevent further growth we fire up the kiln and quickly dry the green malt down to around 5% moisture content. The kiln is also where special colors and flavors are developed depending on the amount of heat. After kilning the malt is cooled down, packaged, and ready to go into our favorite beers, spirits, and baked goods.
The science of malting is in understanding the complex bio-chemical changes taking place to develop beneficial enzymes and the art of malting is figuring out how to do this consistently with an ever changing, living, organism!