It is worth mentioning that many of the new techniques for food drying use superheated steam or inert gases (nitrogen) as the drying medium or are simply intelligent combinations of traditional drying techniques, e.g., combination of heat transfer modes, multi-staging of different dryer types.
Superheated steam as the convective drying medium offers several advantages, e.g., higher drying rates under certain conditions, better quality for certain products, lower net energy consumption if the excess steam produced in the dryer is used elsewhere in the process, elimination of fire and explosion hazard. Use of nitrogen as a drying medium has added advantage of avoiding the oxidation reactions in food drying; however, this is expensive operation and needs closed loop system.
New dryers are being developed continuously as a result of industrial demands. Over 250 US patents are granted each year related to dryers (equipment) and drying (process); in the European Community about 80 patents are issued annually on dryers. Kudra and Mujumdar (2009) have discussed a wide assortment of novel drying technologies, which are beyond the scope of this chapter.
Suffice it to note that many of the new technologies (e.g., superheated steam, pulse combustion – newer gas-particle contactors as dryers) will eventually replace conventional dryers in the next decade or two. New technologies are inherently more risky and more difficult-to-scale-up. Hence there is natural reluctance to their adoption.
Readers are encouraged to review the new developments in order to be sure their selection is the most appropriate one for the application at hand. Some conventional and more recent drying techniques are listed in the Table 3.6. Jangam, Mujumdar – Classification and Selection Drying of Foods, Vegetables and Fruits 77 Table 3.6. Conventional versus innovative drying