**1. Introduction**

Nobody denies that the world is inclining toward alternative sources of energy: a world where human habitats are safe, resilient, and sustainable and where there is universal access to affordable, clean, reliable, and sustainable energy. One of the most important applications of energy is food preservation using drying technology. Preserving food by drying is the oldest method used at home and by food transformation industry. Dried food became an important result, allowing humans to be independent from food supply in any environmental conditions [1]. Food drying techniques have long been applied since ancient times in conventional ways, such as drying in the sun. From the traditional to the most innovative, there are several drying solutions. Depending on the drying method used, the processing time, the product's final quality, or the efficiency of the process can vary considerably. Currently, drying methods have been developed with the latest technology to reduce the damages caused by biochemical changes, which decrease nutritional value during the drying process. Conserving energy and achieving the best quality of dried products have become the most important factors that determine the usefulness and success of operating any drying unit, where heat is transmitted through the drying unit in three forms conduction, convection, and radiation. In this regard, when the temperature of the fresh material increases, the molecular motion gains more energy; as a result, it causes changes in the structure of the material as well as its chemical properties to increase the shelf life and improve the quality [2]. As indicated by [3], literature data reported more than 400 different types of plants. Among them, only 100 different types are applied in practice, design, heat input, operating temperature and pressure, and quality specifications of the final dried product are the main variables considered for building dryers. However, such technologies are expensive, high-energy demanding, and greenhouse gases producing. In the past, food products were dried, exploiting sun energy. In several countries, sun drying is still used for domestic food transformation. At the industry level, the spoilage reduction, in order to improve the stability of dried products during their storage, is an important input to stimulate a great and rapid evolution in drying technology [4]. A lot of published literature in the areas of drying of food products is already available, but often each paper has been focalized on selected types of drying plants. Furthermore, this chapter will shed light more on the most common industrial drying techniques applied in the food processing process, independently from the basic principles on which they are based to build them. In this way, the reader could choose the methodology most adequate to his objective in an easy and fast manner.
