Views: 305 Author: Wendy Publish Time: 2023-07-20 Origin: Site
Freeze drying, often referred to as lyophilization, is a method of removing water that is frequently used to preserve perishable goods in order to increase their shelf life and/or make them travel-ready. In order for the frozen water in the material to directly transform into a vapor (sublimate), the material must first be frozen, followed by a reduction in pressure and the addition of heat.
There are three stages to freeze drying:Using freeze drying properly can shorten drying periods by 30%.
The most crucial step in freeze drying is freezing, and there are numerous techniques for doing it. Freezing can be done on a shelf in the freeze dryer, in a chilled bath (shell freezer), or in a freezer. Sublimation, as opposed to melting, is ensured by cooling the substance below its triple point. This keeps its physical form intact.
Large ice crystals, which can be created by gradual freezing or annealing, are best for freeze drying. The outcomes of freeze drying biological materials, however, are less than ideal because when crystals are too big, they may rupture the cell walls. The freezing is done quickly to avoid this. An option for materials that precipitate is annealing. The product is quickly frozen, and then the temperature is raised to encourage crystal growth.
Primary drying (sublimation), the second stage of freeze drying, involves lowering the pressure and heating the material to cause the water to sublimate. Vacuum accelerates sublimation. Water vapor can stick to and solidify on the cool condenser's surface. The vacuum pump is additionally shielded from the water vapor by the condenser.In this stage, the material's water content is reduced by about 95%. Drying in the initial stages can take time. The structure of a substance can be changed by excessive heat.
Secondary drying (adsorption), the last stage of freeze drying, occurs when the ionically attached water molecules are eliminated.The links between the substance and the water molecules are broken by elevating the temperature above that of the primary drying phase.The materials are still permeable after being freeze dried.The vacuum can be broken with an inert gas after the freeze-drying procedure is finished before the material is sealed.To 1-5% residual moisture, the majority of materials can be dried.
Too much heat applied to the product can result in meltback or product collapse.
An excessive amount of vapor striking the condenser might produce condenser overload.
Excessive vapor production
Excessive surface area
Inadequate condenser space
Not enough refrigeration
Vapor choking occurs when vapor production exceeds the vapor port's capacity (the opening between the product chamber and the condenser), increasing chamber pressure.
Here are a few key phrases related to freeze drying. Visit our freeze drying terms page for a complete list.
Eutectic Temperature or Eutectic Point
is the temperature at which the product will not melt below which it will only exist in the solid state. There may be more than one eutectic point or no eutectic point in some products.
The product's maximum temperature during freeze drying before melt-back or collapse causes it to lose quality.