The combination of vacuum and microwave makes for faster and gentler heat treatment, offering a product of much higher quality than conventional tunnel and spray drying, that is cheaper and faster than freeze drying.
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The technology, which is offered by a Canadian company the Enwave Corporation, was developed at University of British Columbia in 1998. The principal issue appears to be the development of equipment to handle the irriadiation of products under vaccum in continuous large scale operations.
An article published in the South African Food Science and Technology presents some information that supports the technology's claims that were outlined in the first paragraph.