20th Century Innovations Obviously the 20th century could not leave coffee roasting technology alone. In 1934 the Jabez Burns company developed a machine that applied no heat whatsoever to the drum itself, instead relying entirely on a powerful stream of hot air howling through the drum. The Continuous Roaster For large roasting companies time is money, and emptying beans from the roaster and reloading with more beans takes time. Such economic motives lay behind still another 20th century development, the continuous roaster, in which the roasting process never stops until the machine is turned off. The most common continuous roasting design elongates the typical roasting drum and puts a sort of screw arrangement inside it.
Hot air is circulated through and across the drum at the front end and cool air at the far end.
The movement of the beans through the drum is timed so that green coffee entering the drum is first roasted, then cooled by the time it tumbles out at the end of its journey. Variations of this principal continue to be employed in machines used today in many large commercial roasting establishments. As we approach the 21st century there are signs that roasting technology may be undergoing still another revolution. Barring some breakthrough in the use of microwaves, it seemed unlikely that the basic technologies for applying heat to the beans and keeping them moving will change. What is changing is the way the roast is monitored and controlled.