Guest editorial

Abstract

Drying has uses going back into antiquity and research studies dating back well over 150 years. This issue marks the fortieth anniversary of the initiation of Drying Technology. The initiative of the founding Editor Dr. Carl W. Hall who started the journal in 1983 was both timely and prescient. Professor Arun S. Mujumdar has been associated with running of this journal right from the start and took over as the Editor-in-Chief in 1988. Drying has central roles in at least three of the most crucial and vexing problems facing mankind—the need for a sufficient supply of healthful food throughout the world and hence sustainability, the need to address future health crises akin to the recent COVID-19 pandemic, and the need to conquer and control global warming. More and more, good and probing research is needed on many different aspects of drying. Going back to the Incas and before, drying has been a widely used method of food preservation. Not only can drying preserve and stabilize foods, but it can also substantially reduce weight and hence transportation costs. It supplants the use of freezing or refrigeration for both transportation and storage, and provides storage stability that can be decades long. Ordinary drying (often denoted “dehydration” in the business) is hampered by irreversible changes brought about in food quality factors, both nutrients and consistency, and difficulty or incompleteness in rehydrating the product. As well there can readily be losses of flavor and aroma, since the compounds composing those qualities are by their nature volatile, some are heat-sensitive, and many are more volatile than water when in aqueous solution. Freeze drying can overcome these difficulties, but is still a relatively expensive process, carried out through long-duration, labor-intensive, batch processes. Because of cost, the use of freeze drying to preserve foods is presently limited to specialty markets such as stashes of emergency food, backpacking meals, instant coffee, and components of items such as breakfast cereals and pet treats. Research is needed regarding preservation of the various food quality attributes during conventional and other methods of drying. The more that this research can develop understanding at the molecular level and/or be of a generalizable nature, the better. Better understanding is needed of the mechanisms by which water moves through materials of different sorts during drying. Research should also be directed toward the long-sought goal of a commercially viable continuous freeze dryer or an entirely different batch freeze-dryer design for much higher capacities than current operations. Still on the subject of an adequate food supply for the world, more consideration should be given to how use of drying, and particularly the relatively long shelf lives of dried food products, can reduce the large fraction of the world’s food supply that currently goes to waste, currently estimated as 30% to 40% for the United States. Since its original uses for penicillin and blood plasma during World War II, freeze drying has also been the most universally reliable method for stabilization of biologically-active products through dewatering. These uses increased substantially with the development of the biotech industry as of the 1980s. When the COVID-19 pandemic of 2020 arrived, messenger-RNA (mRNA) vaccines were developed impressively rapidly, but required cryogenic temperatures for transport and storage, thereby greatly complicating the distribution of the vaccines. It has been recognized that freeze drying would probably have been a better method of stabilization for transportation and storage. However, established and commercially available batch vial freeze dryers did not provide the wherewithal of carrying it out on such a scale and within the very short time period needed for development. It would help greatly to have a much deeper understanding of what drying conditions are needed to preserve various kinds of biological activity upon reconstitution for various types of substances and uses. It will also be very desirable to have at least a much greater conceptual arsenal of freeze dying or other stabilizing techniques that have been devised, are proven, and can be rapidly implemented on a large production scale. Even more useful could be generic large-scale freeze drying capacity that could be switched to emergency uses if and when needed. Such capacity might also see uses for recovery of water-damaged library books. Finally, because of its energy consumption, drying is an important contributor to global warming. Conservative and now somewhat outdated estimates are that drying accounts for 10% to 15% of total industrial energy consumption and 6% of residential electricity use. Much has been done over the years to increase the thermal efficiencies of evaporators through creative use of heat exchange, multi-effect design, and other means. Increasing the thermal efficiencies of industrial and home drying systems deserves similar attention, despite the greater complexities of handling solids rather than liquids. The addition of clothes dryers to the