Freeze‑dried durian is widely used for baking materials, tea‑drink ingredients and instant snacks. Rehydration ratio directly reflects internal porous‑structure condition and is a critical assessment item for overseas high‑end buyers. For high‑sugar Musang‑King durian, improper process control leads to poor rehydration, insufficient soaking effect and hard pulp. Many factories only focus on outer appearance while ignoring rehydration performance, so products can only enter low‑end sales channels.
Pre‑freezing determines ice‑crystal size and further defines pore structure after sublimation. Ultra‑fast freezing shall be avoided for high‑sugar durian. Tiny ice‑crystals generated by rapid‑freezing leave narrow pores after sublimation and hinder water molecule penetration and lower rehydration performance. Controlled slow pre‑freezing produces moderately‑sized ice‑crystals and forms well‑connected porous channels for better rehydration. However, freezing cannot be excessively slow to prevent juice‑migration and tissue damage.
Do not blindly pursue fast drying in sublimation phase. Too‑fast sublimation easily creates hard surface crust and blocks inner pores. Adopt slow‑sublimation profiles for steady ice escape and well‑maintained inner porous network. Shelf temperature shall rise in mild gradient; steep short‑term temperature‑rise will melt surface sugar and seal pore channels.
Tray‑loading thickness cannot be neglected. Over‑thick pulp layers cause insufficient inner‑layer sublimation and poorly‑developed pore network and degrade rehydration performance. Keep reasonable spreading thickness for durian pulp; spread pieces loosely and avoid heavy stacking. Prevent pulp compressing because compressed raw‑material loses native pores and rehydration cannot be improved even with optimized freeze‑drying parameters.
Besides, fruit ripeness makes big difference. Over‑ripe durian has sharply higher viscosity and poor rehydration even with perfect freeze‑drying curves. Factories shall grade fresh fruits strictly and separate durian of different ripeness for independent batches. Avoid squeezing finished goods after discharging to protect fragile porous structure. Combine hardware, process and raw‑material management to stably achieve rehydration ratio ≥1:5.
