. Some products may not form a good film on the drum
surface and are not suitable for drum drying.
. Some products, especially those with high sugar
content, may not be easily scrapped off from the drum.
. Relatively low throughput compared to spray drying.
. High cost of changing drum surface because of the
precision machining that is required.
. Possible scorching of the product to impart cooked
flavor and off-color due to direct contact with high
temperature drum surface.
. Not able to process salty or other corrosive materials
due to potential pitting of drum surface.