With a freeze dryer, you can get rid of moisture from your products. It will also help in freezing it, thereby reducing the pressure and ensuring that frozen water is converted to gas. The average temperature a freeze dryer works ranges between -40°C and -80°C. Freeze drying retains the nutrients and texture of food, while extending its shelf life.
The 3 Stages of Freeze Drying: How Temperature Determines Their Outcome?
A freeze dryer passes through different temperature stages while working. Each temperature stage contributes to the final product you get. Freeze drying uses regulated pressure and temperature to get rid of moisture from substances without changing their taste, look, and overall quality.
There are three stages involved in the freeze drying process which are freezing, sublimation, and desorption. Each stage works within certain temperature ranges to achieve its objective. Also, the temperature used at each stage must maintain the quality of the product you are freeze drying. Let’s discuss each stage and how temperature determines their outcome.
Freezing
The freezing phase works at a temperature within -30°C to -50°C. It is the first stage in the freeze-drying process which completely turns your product to a solid form. In some cases, you may need to expose some products to colder temperatures based on their composition.
The main objective of this stage is to completely freeze your product. Here, all water content in your product will turn into ice. This stage gets your product ready for the sublimation phase. If your product doesn’t freeze well during the freezing stage, it will cause spoilage during drying.
You should also take note of the freezing speed during this phase. Rapid freezing preserves the microstructure of your product due to the formation of small ice crystals. Slow freezing, on the other hand, creates large crystals. This can damage biological or sensitive food products.
Therefore, it is important to ensure a consistent temperature during the freezing stage.
Sublimation
After the freezing phase the pressure of the chamber declined while temperature slightly better increased to ~-10°C to -20°C. This is also the primary drying phase where the chamber creates vacuum after reducing its pressure. The temperature then increases for the sublimation phase to kick start.
In this stage, the ice in your product changes from the solid state to vapor without turning to liquid. This can only work when the pressure is low. The sublimation process is what helps the product to maintain its structure, look, and nutritional value.
During this process, the freeze dryer removes about 95% of the moisture. However, the temperature needs careful regulation for good results. The ice will melt instead of turning into gas if the temperature increases too quickly. If your vacuum is weak, the sublimation drops, extending the process. In the long run, this will compromise the end result.
The sublimation stage needs proper temperature regulation. Therefore, it is important you use pressure and temperature sensors to maintain a balanced temperature during this stage. The sublimation period may last longer based on the texture and volume of the product you are freeze drying.
Desorption
This is the last stage in the freeze drying process where the temperature rises to 20°C–30°C. Here, the remaining moisture in the product is removed. After the sublimation phase, there is a small amount of moisture left in the product. Therefore, the desorption phase gets rid of this moisture to ensure long-term stability. The temperature increases while the chamber is under vacuum. The heat removes the remaining moisture in the product without affecting its composition.
Although the desorption gets rid of a small amount of water, this phase preserves the quality of your product and extends its shelf life. Without desorption, the remaining moisture in your product can cause microbial growth.
The desorption phase uses high temperature to remove moisture. However, this temperature must not be high enough to affect the active ingredients in your product or change its texture or taste.
Factors That Impact the Operating Temperature of Your Freeze Dryer
The operating temperature of your freeze dryer varies depending on some factors. These factors include;
Type of Product (Food vs. Pharmaceuticals)
Pharmaceutical products should be under low temperature to preserve their active ingredients. Food products, on the other hand, can withstand higher temperatures based on their nutrients, texture, and taste.
Moisture Content
The remaining moisture content in your product after the primary drying phase will determine the temperature required to remove bound moisture. Products that need longer shelf life will need higher temperature for secondary drying.
Capabilities of the Equipment
The design features of your freeze dryer which include vacuum strength and cooling capacity will determine the temperature limits. While some freeze dryers can safely operate at high temperatures, some can’t.
Product Texture and Volume
If you are dealing with thick and high-volume products, your freeze dryer will operate at lower temperatures. Also, this will take longer cycles for the moisture to remove completely.
Conclusion
Freeze dryers work at a particular operating temperature depending on a number of factors by material type and product size. While each phase of the freeze drying process works at a different temperature level, you need to monitor the operating temperature of your freeze dryer.
