Energy-efficient food drying for sustainable preservation: A review of technologies and performance

Food drying is indispensable for preserving plant-based foods, yet it remains an energy-intensive unit operation with material implications for nutrition retention, greenhouse-gas emissions, and processing costs. Conventional hot-air and sun-based dryers remain widely used but are often characterized by high specific energy consumption (SEC), long residence times, and degradation of heat-sensitive nutrients. This review synthesizes advances in food drying technologies for plant-based products, spanning solar-assisted and hybrid solar dryers (including thermal storage), heat-pump dehumidification and closed-loop systems, microwave and radio-frequency volumetric heating, infrared radiative drying, vacuum and freeze drying, refractance window drying for purées, and emerging intensification routes such as ultrasound assistance, pulsed electric field pretreatment, and electrohydrodynamic drying. Reported studies indicate that advanced and hybrid drying systems, particularly heat-pump-based and staged hybrid configurations, can achieve SEC values on the order of ∼1–2 kWh·kg⁻¹ H₂O removed, corresponding in many cases to roughly 30–50% reductions relative to conventional hot-air baselines, while shortening drying times by up to ∼70% for suitable product geometries and loadings. For many fruits, vegetables, herbs, and plant-derived ingredients, these regimes support ≥80% retention of key heat-sensitive nutrients and bioactive compounds. When coupled with low-carbon electricity, waste-heat recovery, or solar assistance, reported drying-stage carbon intensities can be reduced to approximately ∼0.4–0.6 kg CO₂-eq·kg⁻¹ dried product. Techno-economic evidence further indicates that heat-pump and mixed drying systems can deliver payback periods below ∼5 years under moderate-to-high utilization and prevailing industrial energy prices. Overall, the review emphasizes that no single technology is universally optimal and provides a decision-oriented synthesis to guide technology selection and process integration toward energy-efficient, low-carbon, and quality-preserving food drying.