Freeze drying is "low-temperature dehydration", while drying is "high-temperature evaporation". The two are completely different in terms of principles, effects, costs, and application scenarios. Essential difference: The physical path is completely different. Freeze drying (vacuum freeze-drying) and drying (hot air/conduction drying) are the core principles. Sublimation: solid ice → gaseous water vapor (skipping liquid state). Evaporation: liquid water → gaseous water vapor. Temperature environment is low (-30 ℃~-50 ℃ freezing, the entire drying process is below 0 ℃). High temperature (40 ℃~200 ℃, depending on the material). Pressure environment is high. Vacuum (pressure<60Pa). Normal pressure or micro negative pressure. Water removal path: Ice crystals directly sublime into water vapor, which is captured by a cold trap and vaporized by heat, and carried away by hot air. For example, drying: like placing a wet towel on a radiator, heat "bakes" water into steam and runs away. Freeze drying: It's like freezing a wet towel into ice cubes and then placing it in a vacuum chamber, where the ice "disappears" into water vapor while the towel remains in its original fluffy shape. 2、 The impact on materials: The vast difference is the core decision-making basis for choosing between freeze-drying or drying. The table dimension of freeze-drying and drying has extremely high retention of nutrients (vitamin C retention rate>90%, almost zero loss of active protein) and low retention (vitamin C loss over 50%, thermal sensitivity variable). The color maintains its original color (vacuum environment inhibits oxidative browning) and is prone to browning (high temperature accelerates Maillard reaction and enzymatic browning). The shape does not deform (porous sponge like, with basically unchanged volume), and the shrinkage and wrinkling (cell wall collapse) are excellent in rehydration (restored to its original state after soaking in water in 5 seconds) and poor in rehydration (soft and rotten after rehydration, unable to restore to its original state). The taste is crispy, fluffy, dry and hard, and chewy. The shelf life is long (moisture content of 1%~5%, sealed at room temperature for 1-3 years) and relatively short (moisture content of 5%~15%, moisture-proof). Meaning: The current humidity in Shanghai is high, and if the dried materials are not sealed properly, they may absorb moisture and mold within 3 days; Freeze dried products, due to their extremely low moisture content and dense structure, have stronger resistance to moisture absorption. 3、 Equipment and Cost: Freeze drying is expensive due to the "vacuum+low temperature" table dimension. Freeze drying equipment has high complexity (requiring refrigeration system, vacuum system, cold trap, control system) and low cost (heat source+fan+box is sufficient). The equipment price is expensive and the energy consumption is high (continuous operation of vacuum pump+refrigeration system, high power consumption), while the energy consumption is low (mainly heating and fan energy consumption). The processing time is long (usually 20-40 hours per cycle) and short (usually 4-12 hours)

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