Food unit operations refer to the engineering processes involved in transforming raw materials into desirable food products, taking into account the main laws and principles that govern the physical, chemical, and biochemical changes related to these processes. Drying is one of the most common unit operations used in the food sector to reduce food water content, thereby extending shelf-life, reducing weight and volume, and decreasing inventory and transportation costs. Traditionally, food materials are dried using conventional methods, such as natural solar drying and hot air drying. However, recent years have witnessed the introduction of several emerging technologies (e.g., infrared drying, microwave drying, and freeze drying) that have promising potential to overcome challenges, such as uneven drying, poor sensory properties and nutrient loss, and large energy consumption. More interestingly, recent developments and advancements in digital, physical, and biological technologies, spurred by the Fourth Industrial Revolution (Industry 4.0), have significantly impacted various food manufacturing operations, including food drying. Growing evidence shows that diverse Industry 4.0 technologies (notably artificial intelligence, the Internet of Things, smart sensors, digital twins, and big data) can be harnessed to improve the modelling, monitoring, prediction, and optimization of various parameters in food drying. These technological advancements are not only accelerating the pace of innovation but also enhancing process efficiency and overall performance in intelligent food drying, ushering in the era of "Food Drying 4.0."