At the simplest level, malting and brewing represent the conversion of the starch of barley into alcohol. Brewers are interested in achieving this with maximum efficiency, in terms of highest possible alcohol yield per unit of starch. At the same time, though, they insist on consistency in all other attributes of their product—foam, clarity, color, and, of course, flavor.
When we speak of barley in a brewing context, we are primarily concerned with its grain, the seeds growing on the ear in the field: it is these that are used to make beer. Barley grains are hard and difficult to mill. Try chewing them if you will—but have a good dentist on hand! They also don’t taste particularly pleasant, drying the mouth and leaving a harsh, astringent, and extremely grainy aftertaste. Indeed, beer brewed from raw barley is not only troublesome in processing but also has a definite grainy character.
It must have been pure serendipity when the process of malting was discovered some 100 centuries ago, but out of such happenstance has sprung up a mighty industry responsible for converting this rather unpleasant cereal into a generally satisfying malt.
[Source: Tap Into the Art and Science of Brewing]