In order to preserve a perishable material, a freeze laboratory freeze dryer will remove the water from the material. This will either increase the material's shelf life or make it more convenient to transport. Freeze dryers work by first freezing the material to be dried, then lowering the pressure and adding heat to create an environment in which the frozen water in the material can sublimate, or change directly into a vapor state.

There are three stages to the operation of a freeze dryer:

• Freezing

• Initial Drying, also Known as Sublimation

• The Adsorption Stage of Secondary Drying

• When done correctly, freeze drying can cut drying times by up to 30 percent

   

Phase 1: FreezingPhase
Graph illustrating the operation of a freeze dryer, as well as the ideal pressure and temperature for the freeze drying process

Freeze Drying vs. Dehydrating How are they Different?

This is the most crucial stage of the process. The process of freezing a product in a freeze Drawell can take a few different forms.

The process of freezing can take place on a shelf in a freeze dryer, in a chilled bath (shell freezer), or in a traditional freezer.

The material is cooled to a temperature that is below its triple point in the freeze dryer, which ensures that sublimation will occur rather than melting. This ensures that the material retains its original physical form.

Large ice crystals, which can be created by either gradually freezing the water or annealing it, are the most amenable to being freeze-dried by a freeze dryer. When it comes to biological materials, on the other hand, crystals that are too large can rupture the cell walls, which results in less-than-desirable outcomes for the freeze drying process. This is why the freezing process is carried out as quickly as possible.

Annealing is a process that can be utilized for materials that have a tendency to precipitate. In this method, the liquid first undergoes rapid freezing, and then the product's temperature is increased so that crystals can form.

Phase 2 is the primary drying process, also known as sublimation.

The second phase is called primary drying, and it is also known as sublimation. During this phase, the pressure is lowered on the material, and heat is added so that the water can sublimate.

The vacuum in the freeze Drawell accelerates the process of sublimation. The cold condenser of the freeze dryer offers a surface to which the water vapor can adhere and become solidified. Additionally, the condenser shields the vacuum pump from the water vapor that may be present.

During this phase, approximately 95% of the water that was present in the material is evaporated.

The primary drying stage is often a drawn-out process. An excessive amount of heat can cause the material's structure to become altered.

The third phase is called the secondary drying, or adsorption.

The last phase is called secondary drying and it is accomplished through adsorption. During this phase, the ionically-bound water molecules are dehydrated.

The bonds that held the material and the water molecules together are severed when the temperature is raised to a level that is higher than that of the primary drying phase.

Freeze dried materials retain a porous structure.

Before the material is hermetically sealed, the vacuum created by the freeze freeze dryer can be broken using an inert gas once the process has been completed.

The residual moisture in most materials can be reduced to between 1 and 5 percent after drying.

Problems to Avoid When Using a Freeze Dryer:

• If the product is heated to a temperature that is too high, it may melt back or the product may collapse

• Overheating of the condenser as a result of an excessive amount of vapor entering it

• An excessive amount of vapor productionAn excessive amount of exposed areaA condenser area that is too small

• Unsuitable levels of refrigeration

   

Vapor choking occurs when more vapor is produced than can pass through the vapor port, which is the port located between the product chamber and the condenser. This results in an increase in chamber pressure.

Important Terms
The following is a glossary of terms that are relevant to freeze dryers. See the terminology page for our freeze drying process for a complete list there.

The point at which the product can only exist in the solid phase; also known as the eutectic point or eutectic temperature. This point corresponds to the lowest temperature at which melting can occur. It's possible that some products don't have a eutectic point at all, or that there are more than one.

During the freeze drying process, the critical temperature is the highest temperature that the product can reach before its quality begins to deteriorate due to melt-back or collapse.

When the substance is frozen, crystals are formed, and it either has a single eutectic point or multiple eutectic points. Crystalline. Crystals formed by rapid freezing are typically difficult to dry, but annealing can facilitate the formation of larger crystals.

A multi-component mixture is said to have amorphous properties if it does not crystallize and does not have a eutectic point. They transform into a type of glass. In order to be successful, freeze drying must be carried out at a temperature lower than the glass transition point.

The point at which the product has become so pliable that it is no longer able to support its own structure is referred to as the collapse point. This presents a number of challenges, including the following:

• Disintegration of the physical structure

• Insufficiently dried out

• Decreased ability to dissolve

• A great deal of ablative activity (splat)