Malt is produced from gain, usually barley. Barley is excellent for brewing beer because it contains a lot of starch, which can be converted into fermentable sugars. Before it's used in brewing, the barley grain is usually malted for the purpose of developing enzymes that convert the complex starch into sugars.
Next step of the process is mashing. Having been crushed in the malt mill, the milled grains are mixed with water in the mash kettle where the temperature is gradually increased to the desired level to activate and control the enzymes.