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PRINCIPLE. The main principle involved in freeze drying is a On 21st century, in pharmaceutical field lyophilization has become important. Lyophilization, or freeze drying, is a process in which the solvent (usually water) is: first frozen and then. – removed by sublimation in a vacuum. Freeze drying, also known as lyophilisation or cryodesiccation, is a low temperature . Bulk lyophilization of APIs is typically conducted using trays instead of glass vials. .. Food processing technology: principles and practice ( 4th ed.).

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This part of the freeze-drying process is governed by the material’s adsorption isotherms. As shown below on the phase diagram for water, low pressures are required for sublimation to take place.

Factors affecting secondary terminal drying phase: Advances in Food Dehydration. In these examples, Point D on the curve, Fig 1 and Fig 2 represent the temperature of the complete freezing of the product. Inside the neck of the bottle, which has a diameter of about 3mm, or a section of 7cm2 7 x m2the speed is calculated at:.

Samples are generally placed in containers such as glass vials that are placed on the shelves within the vacuum chamber. It is important that at the end of secondary drying, the refrigeration system must be capable of lowering the temperature of the ice condenser to a temperature low enough to obtain the necessary residual moisture in the product.

The process condenser consists of refrigerated coils or plates that can be external or internal to the chamber. To accomplish this goal, it is vital to insure the same parameters for each operation.


Pretreatment includes any method of treating the product prior to freezing. This plasma could potentially burn the sample, so maintaining a microwave strength appropriate for the vacuum levels is imperative. This very often makes dissolution difficult. Due to the low processing temperatures and the minimization of deterioration reactions, nutrients are retained and color is maintained. Freeze-drying is viewed as the optimal method of choice lyyophilizer dehydration because of the preservation of quality, meaning characteristics of the food product such as aroma, rehydration, and bioactivity, are noticeably higher compared to foods dried using other techniques.


In considering a freeze dryer for production use, the following general guidelines should be a part of your determinations:. Slower shelf cooling rates do not necessarily yield larger ice crystals because of the effects of lophilizer. In addition to defrosting the condenser and cleaning the system after each cycle, routine freeze dryer maintenance typically includes periodic changing of vacuum pump oil and visually checking all seals and gaskets.

Freeze-drying – Wikipedia

Once the product is frozen, the vacuum pump evacuates the chamber and the product is heated. It is best not to freeze a large block of sample in the bottom of a flask because the sample will be too thick for efficient water removal.

Lyophilization and freeze drying are terms that are used interchangeably depending on the industry and location where the drying is taking place. Water can also cause mold to grow or make inks bleed. Sublimation, and the qualities of the finished product are greatly dependent on this crystal structure. The shelves play a major role as they behave like heat exchangers at different times of the freeze-drying process.

Provide a simple cleaning operation. Product is either pre-loaded into vials which are then transferred to the shelf or it is loaded in bulk form directly onto a product tray. Products with excipients may exhibit tendencies to retain water in the matrix, and are hygroscopic in ambient air. Coffee contains flavor and aroma qualities that are created due to the Maillard reaction during roasting [17] and can be preserved with freeze-drying.

Special containment systems such as glove boxes are required for freeze drying certain products, especially when toxic materials are present. As the product is porous, it can be re-dissolved by the simple addition of a proper solvent.

The cycle time can often be substantially reduced by investigating several factors:. Cooling elements within the shelves freeze the product.

This heat input does not melt the product because an equivalent amount of heat is removed by vaporization of the solvent. This method can be very complicated to setup and run as the microwaves can create an electrical field capable priinciple causing gases in the sample chamber to become plasma.


Visual and functional characteristics of the dried product pirnciple also important for many applications. A rise in chamber pressure. Atmospheric pressure torr we derive: When the product temperature equals the shelf temperature, it can be inferred that primary drying is complete. The process lyophiilzer lyophilization consists of:.

Freeze Drying can only take place if the partial pressure of the vapor in the drying chamber is lower than the water vapor pressure above the product.

General Principles of Freeze Drying | American Lyophilizer, INC.

These products can benefit from a thermal treatment process, which is also called annealing. Radiant freeze dryers use infrared radiation to heat the sample in the tray. However, at this stage the product is not sufficiently dry for long term storage.

Insure the necessary low temperature saturated suction during the secondary drying to deliver the lower vacuum levels needed for this phase. The partial pressure of the vapor surrounding the product must be lower than the pressure of the vapor from the ice, at the same temperature.

Several analytical methods are available for determining that primary drying is complete.

Infrared radiation heating allows for a very uniform heating of the surface of the product, but has very little capacity for penetration so it is used mostly with very shallow trays and homogeneous sample matrices.

Sublimation requires heat energy to drive the phase change process from solid to gas. During annealing, the product temperature is cycled for example: This simple control will greatly improve the energy transfer and lyophilier primary drying times.