Drying is the removal of moisture from foods to a desired low level, one of the oldest and most widely used preservation methods, operating by lowering water activity below the thresholds for microbial growth and enzymatic spoilage. Techniques range from traditional sun and air drying through hot-air tunnel drying to advanced freeze drying and spray drying, each suited to different products and quality targets. Effective drying requires control of temperature, humidity, and airflow to avoid case hardening, where a dry crust traps interior moisture, and to protect heat-sensitive nutrients and colours. Because it concentrates flavours and reduces weight and volume, drying also cuts transport and storage costs, making it central to the trade in fruits, vegetables, dairy powders, and instant foods.