Why freeze drying

This form of preservation not only extends the shelf-life of foods, but has also been shown to lock in important nutrients and enhance flavor of things like fruits, vegetables, meats, and even coffee. To successfully freeze dry a sample, your equipment will need to meet certain requirements. First, the collector coil of your freeze dryer will need to be degrees colder than the freezing point of your sample in order to trap the water vapor that is being released.

You will also need a vacuum pump that can reach a minimum of. This deep vacuum establishes negative pressure, forcing the free-flowing water molecules that have left the sample via sublimation to evacuate the environment around the sample and travel to the collector coil. You will also need to have a drying accessory, such as: a manifold, chamber or tray dryer, and glassware or trays to contain your sample.

Although not required, an end-point detection system makes the sometimes days-long freeze-drying method easier to manage by keeping you informed of when your sample has finished drying. There are three stages in the lyophilization process: Pre-freezing, primary drying, and secondary drying. The pre-freezing stage is the most important stage of the freeze-drying process. In this stage, sample material will need to be cooled to at least the temperature of the melting point for that sample.

This ensures the sample will be completely frozen and can then undergo sublimation. The rate at which your sample freezes will affect the size of the ice crystals that form. If not done properly, it can impact the speed of reconstitution, length of the freeze-drying process and integrity and stability of your sample.

Larger ice crystals facilitate faster and more efficient lyophilization because water molecules are able to move more freely out of the sample during sublimation. For samples like food or tissues, large crystals can break the cell walls and damage your sample. In these situations, it is best for freezing to be done quickly through flash freezing, creating smaller ice crystals.

Freeze drying is the process of dehydrating frozen foods under a vacuum so the moisture content changes directly from a solid to a gaseous form without having to undergo the intermediate liquid state through sublimation.

In this process, freeze dried food maintains its original size and shape with a minimum of cell rupture. Removing moisture prevents a product from deteriorating at room temperature. The process is used for drying and preserving a number of food products, including meats, vegetables, fruits, and instant coffee products. The dried product will be the same size and shape as the original frozen material and will be found to have excellent stability and convenient reconstitution when placed in water.

Freeze dried products will maintain nutrients, color, flavor, and texture often indistinguishable from the original product. Depending on the product and the packaging environment, freeze dried foods are shelf-stable at room temperature for up to twenty-five years or more, if canned, and between 6 months to 3 years if stored in a poly-bag container, making it perfect for survival food or food storage as well as for commercial use.

The main determinant of degradation is the amount and type of fat content and the degree to which oxygen is kept away from the product. Simply put, freeze-drying is the removal of water from a frozen product using a process called sublimation. Primary drying can be a slow process.

Too much heat can alter the structure of the material. By raising the temperature higher than in the primary drying phase, the bonds are broken between the material and the water molecules. Freeze dried materials retain a porous structure.

After the freeze drying process is complete, the vacuum can be broken with an inert gas before the material is sealed. Here are a few important freeze drying terms. For a comprehensive list, see our freeze drying terminology page.

Is the point at which the product only exists in the solid phase, representing the minimum melting temperature. Not all products have a eutectic point or there may be multiple eutectic points. During freeze drying, the maximum temperature of the product before its quality degrades by melt-back or collapse. Multi-component mixtures which do not crystallize and do not have a eutectic point. The point at which the product softens to the extent that it can no longer support its own structure.

This can be a problem for many reasons:.