What's Freeze Drying?

Freeze drying/lyophilization, what's it?

Lyophilization is the process of freeze drying, with many other names such as vacuum freeze drying, sublimation drying, lyophilization, liofilizador,liofilizacion, they are synonymous. Freeze drying is a dehydration way typically use to remove water from materials by sublimation process (working by frozen the material and then reduce surround pressure allow solid water direct vapor to gas, the process skip liquid phase, and finish in low temperature).

water triple point phase

Freeze dried features, benefit and advantage:

Freezing raw material and enable it drying under vacuum, dried products well keep its original shape, almost all nutrition remained because of only water removed, dried products with spongy internal formed by water escape and microchannel leave, thus could rapid rehydrate by add water or solvents, we could say freeze drying is the most perfect way to dry products that have minimum damage to raw material or lossless drying. Freeze dried products could storage in room temperature and lasting up to 25 years.

Freeze Drying steps:

 

1, Freezing stage

Thoroughly freezing the raw material to solid phase, could be done in a Freeze Dryer Lyophilizer (if shelves with freezing function) or in one deep freezer. The keys of freezing is find out raw material’s eutectic point and make sure freezer temperature is lower than that, freezing stage is the insurance of dried products’ physical shape.

 

Some material, especially fluid, the freezing stage may also involve annealing treatment(rapid freezing cause large ice crystals, proper raise its temperature allow ice crystal grow), which could help protect cells from broken as well as short the drying time.

 

2, Primary drying.

Primary drying mainly remove water by sublimation, in this stage, water in solid phase sublimate to vapor and move to ice condenser, freezing on condenser coils surface, in this stage >95% water have removed.

 

In this stage gradually and proper increase the shelves temperature could speed up the sublimation, but too much energy supply may cause glass transition.

 

3, Secondary drying.

Secondary drying process could remove the adsorption water, in this stage need higher temperature and vacuum, after secondary drying, the shelves could reduce temperature and prepare harvest.

Freeze drying is Batch Drying:

 

The freeze drying is a batch process, and most freeze dryer do this way, this is due to the slow sublimation rate of moisture under vacuum (drying rate abt. 1mm/hr), most food material drying time between 14 to 24hrs and pharmaceutical or biological may take few days as per its drying recipe, One vital part is operator need continue optimize the freeze drying recipe, so that reduce freeze drying cost.

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