After rinsing and removing blemishes, blanch most vegetables pretreat fruits if necessary to prevent browning meats can be freeze-dried cooked or raw casseroles are typically assembled from already cooked foods. Food is prepared for freeze-drying the same way food is prepared for regular freezing. Advantages and Disadvantages Advantages of Freeze-drying Therefore, it is safe to place properly dried or freeze-dried foods in vacuum packaging or in containers that also have oxygen absorber packets placed inside. Fortunately, without moisture (water) the botulism bacteria (and all bacteria, yeast, and molds) cannot grow. In fact, removing oxygen from a package may make it more of a concern for the botulism bacteria to grow and produce toxin if there is a moist environment. Remember, vacuum packaging is not a food safety process itself. As long as the food is dried to a low residual moisture, vacuum packaging is safe. Can freeze dried foods be safely vacuum packaged? Examples are raw meats, raw seafood, raw eggs, and foods containing these raw ingredients. Food items that are traditionally cooked before eating must also be cooked before eating as a freeze-dried food. Therefore, when home freeze drying raw foods the microorganisms on those raw foods will remain viable, then activate upon rehydration. In fact, scientists use a laboratory version of freeze drying to preserve microorganisms for future studies because the microorganisms can be rehydrated alive for decades (see Kupletskaya & Netrusov, 2011). The microorganisms stay viable, but dormant, even under the extreme conditions of freeze drying. What happens to microorganisms in the freeze-drying process? Proper safe food handling techniques were employed in the preparation of the food prior to freeze-drying.Drying foods safely is defined as reaching “a safe residual moisture level.” To determine this at home, most Cooperative Extension resources suggest that foods should be dried to a “crisp” or “breakable” texture, although foods with high levels of sugars, such as fruits, may be flexible, but not sticky, when correctly dried (Andress, Harrison, Reynolds, and Williams, 2014).Pre-refrigerated or pre-frozen foods can be placed in the freeze-dryer to minimize this concern. For example, chilling foods safely is defined as reaching 41☏ (refrigeration temperature) in 1-4 hours or less.The freezing process must be quick and the vacuum process should leave only residual moisture.The two sub-processes, freezing and vacuum drying are done correctly:.When these two steps are properly completed, the food is dry enough to allow for safe storage at room temperature. This includes removing the water vapor that was once inside of the foods. The air and water vapor (gas) are removed from the food processing chamber using a vacuum pump. Once frozen, foods are subjected to vacuum drying. The colder the freeze the more efficient the next step will be. Using sublimation, the food retains much of its original texture, flavor, and nutrition when rehydrated.įreeze drying is broken down into two simple processes: freezing and vacuum drying. Freeze drying takes advantage of the scientific principle of “sublimation,” the direct transition of a solid to a gas, by removing ice (the solid) from frozen food as water vapor (a gas).
The process consists of three separate, unique, and interdependent processes freezing, primary drying (sublimation) and secondary drying (desorption)” (FDA Inspection Guides, 7/93, updated 2014). The Science Behind Freeze Drying What is freeze drying?Īccording to the FDA: “Lyophilization or freeze drying is a process in which water is removed from a product after it is frozen and placed under a vacuum, allowing the ice to change directly from solid to vapor without passing through a liquid phase. The advertising is enthralling, the possibilities seem endless: Space-age food at the push of a button! Never waste a leftover again! Gleaming, inviting, New Age-the siren call to Americans who love their gadgets.īut is a home freeze-dryer the appliance for you? Here is some information designed to cut through the advertising hype and provide a voice of reason on the pros and cons of home freeze-dryer ownership. Buying a Home Freeze-Dryer: What to Know Before You Goįreeze-dried foods are extremely popular among backpackers and culinary masters, and now freeze-dryers are available for home use.
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