Drum Roaster is the modern development of an older device, the ball roaster. See ball roaster. Both roasters work on essentially the same principle. They are enclosed chambers that rotate around a horizontal axis and heat up foodstuffs until they darken and acquire a nutty to burned flavor. But, whereas in a ball-shaped roaster grains collect at an uneven depth, in a horizontal drum, fitted with air vents, the material is processed evenly and homogeneously. To produce roasted malt, the maltster places kilned pale malt into the drum for to 2 to 3 h at a temperature of approximately 250°C (482°F). The longer the time and the higher the temperature, the roastier and darker will be the malt. Alternatively, the maltster may place moist green malt from the germination chamber into the drum and heat it there with the vents open or closed. With the vents open, the malt is kilned like regular malt and then turned into roasted malt. With the vents closed, the grain remains moist and undergoes a stewing cycle, at approximately 60°C to 72°C (140°F to 162°F), during which malt enzymes convert starches to sugars, creating caramelized malts. Such homogeneous saccharification is not possible in kilns. After caramelization, the malt may be transferred to the kiln for a final drying to make Carapils®, for instance, or it may stay in the drum with the vents open at about 120°C to 180°C (roughly 250°F to 355°F) to make amber to red caramel malts, such as Caramunich®. In either case, the sugars caramelize into sweet, glassy, crystalline, unfermentable dextrins. Depending upon the degree of caramelization, these malts can lend body, color, flavor, aroma, and foam stability to finished beers.

Drum roaster in action at the Weyermann® Malting plant in Bamberg, Germany. Drum roasters are used to roast malt, darkening the grains, and providing a nutty or burnt flavor. photograph by denton tillman

See caramel malts, crystal malt, and dextrins.