To start, sprouted barley after four days of germination is fed directly into rotating drum roasters similar to those used to produce coffee or cocoa. The malt is still green and growing and contains about 42% moisture. The drum is rotated and slowly heated to bring the grain temperature up to starch conversion temperature, roughly 150 ºF (65.6 oC), just as is done in the mashing process in the brewery. As in mashing, the native amylase enzymes activate and turn the wet starch in the kernel into simple sugars. Because there is so little moisture, this gooey sugar stays inside the kernel. Its like millions of little mash vessels with wort trapped inside. Once conversion is complete, the maltster turns up the heat and begins drying out the malts. Very quickly the sugars are concentrated and the temperatures are taken high enough (>300 oF, 149 oC) to achieve carmelization of the sugars.
