Freeze dryer recipes or freeze drying curve
The freeze dying recipes or drying curve is a system contains several steps with different temperatures and lasting time, by intelligent controller, the steps are linked together, one finish, another one automatic execute until lyophilization (freeze drying) process complete finish, different range freeze dried products recipes may little different, the goal and function of Freeze Dryer recipes is dry products with less time and ensure products’ quality and consistency between batches.
One complete freeze drying recipes include freezing stage, temperature raise stage, temperature reduce stage.
1, Freezing stage.
Freezing stage mainly turn raw material to solid phase, complete frozen, make sure the sublimation drying successful, the process need done under raw material eutectic point which means freezer temperature need lower than material’s eutectic point. e.g. raw material eutectic point (complete frozen temperature) is -25℃, the freezer temperature should lower than it: -30℃ or -35℃ freezer is recommend.
Not all material, some of the raw material freezing stage may also involve annealing(meltback), (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.
Perfect freezing stage insure the freeze dried material keep its original(or frozen) shape, structure, success freezing drying and could short freeze drying time.
2, Temperature raise stage.
The freezing drying recipe some aspects means provide extra heat/energy to shelves/materials, help and speed up the sublimation process, normally the temperature and energy provide step by step, because different time need different amount energy, the control system only executes the temperatures and lasting time you set. Too much energy send to raw material in short time may “melt” it (glass transition) cause material lose structure and freeze drying fail. Too much energy also may cause much vapor in drying chamber and ice condenser cannot freezing it on coil surface on time, if vapor go to vacuum pumps will cause pump broken.
Even you can set tens steps use for temperature raise, but generally principle setting in this stage are: beginning with less time and energy need, temperature may step to 20C and last 2 to 3hrs, in middle need last longer to support continue sublimation, temperature mostly around 50C and last several hours.
During the temperature raise stage, shelves temperature will different with raw material because offset by sublimation, with water removed and remain less and less in raw material, the raw material temperature will close to shelves temperature until same.
As well, this stage, ice condenser temperature, vacuum degree, if you check real-time curve, may instability, this is because of vapor gas fulfill drying chamber cause pressure change and ice condenser coils collect vapor have temperature raise.
3, Temperature reduce stage.
When raw material temperature is same with shelves, that means the drying process almost finish, only need 1 or 2 more hours provide insurance could judgement the drying success.
As the last things before freeze dried/liofilized material harvest, cooling the raw material is very important, mostly could be 30C or 40C, cool the material to proper temperature before harvest could guarantee its stability after expose in environment and for quick package.