Refractance Window Drying: Mechanisms, Quality, and Smart Control

Refractance window drying (RWD) has emerged as a high-efficiency, low-temperature dehydration technology. It enables the production of superior-quality dried foods with minimal nutrient and color degradation. This review synthesizes the mechanistic foundations of RWD, detailing how thermal conduction, infrared radiation, and evaporative cooling interact to create the characteristic "refractance window" that accelerates drying while preserving heat‑sensitive compounds. We critically analyze heat‑ and mass‑transfer behavior, film-product interactions, and microstructural evolution, linking these mechanisms to measurable quality outcomes such as phytochemical retention, rehydration capacity, and sensory attributes. Comparative assessments with conventional and emerging drying technologies highlight RWD's advantages in energy efficiency, process simplicity, and product integrity. The review further integrates recent advances in smart process control, including machine‑vision monitoring, data-driven modeling (e.g., Internet of Things [IoT] and machine learning), and artificial intelligence (AI)‑enabled optimization, which are transforming RWD into a predictive, controllable, and scalable industrial process. However, these approaches remain largely at the experimental and developmental stage, with limited validation in continuous or industrial-scale systems. Finally, we identify key research gaps and propose a roadmap for model‑based design, sensor integration, scale‑up strategies, and sustainability evaluation, positioning RWD as a promising technology for next‑generation food processing systems.