Process of Freeze-Drying
Freeze-drying is a technique by which material is frozen, then dehydrated by sublimation, with complete retention of form. Sublimation is the process by which the contained water passes from a frozen to a gaseous state. Frozen material is placed into a vacuum chamber where the freeze-drying process takes place.
Process:
Freeze drying food uses a process called lyophilization to lower the temperature of the product to below freezing, and then a high-pressure vacuum is applied to extract the water in the form of vapour. The vapour collects on a condenser, turns back to ice and is removed. Finally, a gradual temperature rise extracts all remaining moisture from the product. This process retains the physical structure of the food product and preserves it for re-hydration at a later date.
Process:
Freeze drying food uses a process called lyophilization to lower the temperature of the product to below freezing, and then a high-pressure vacuum is applied to extract the water in the form of vapour. The vapour collects on a condenser, turns back to ice and is removed. Finally, a gradual temperature rise extracts all remaining moisture from the product. This process retains the physical structure of the food product and preserves it for re-hydration at a later date.
5 other food that use the same method.
There are many food/ food products that are used in the method of freeze-drying. Below i have listed 5 food items that use the method of freeze-drying. The following foods include:
1. Fruit
2. Vegetables
3. Meat
4. Fish
5. Ice-cream
1. Fruit
2. Vegetables
3. Meat
4. Fish
5. Ice-cream
How does Freeze-Drying prevent food spoilage?
Food spoils when microorganisms, such as bacteria, feed on the matter and decompose it. When using the food preservation technique of freeze-drying, the liquid (water) is dried out of the product. From taking this liquid out of the product this gives the product a longer shelf life and also keeps nasty micro-organisms out such as enzymes, bacteria, yeasts and mould. This method also preserves the products texture, colour and flavour.
A you can see, the image above show both fresh and freeze-dried carrots. You can defiantly not that the freeze dried carrots have no moisture at all. This may make them unattractive but when you allow moisture in them (by adding water) they taste just as good as fresh carrots but also have a much longer shelf life date. The fresh carrots on the other hand look attractive and taste great but spoilage to fresh carrots rotten quicker and easier as they have not been preserved at all.
What is the suitiable storage method for Freeze-Drying Products?
Freeze-dried food products are best to be stored in a cool and dry places. Storing these products in these places allows to product to be preserved better and also make sure that all moisture and micro-organisms are kept out.
What are the Advances of Freeze-Drying?
Improved freeze drying techniques are being developed to extend the range of products that can be freeze dried, to improve the quality of the product and to produce the product faster. Ever since the 1930s, industrial freeze drying had been dependent on a single type of equipment: the tray freeze drier. In 2005 a quicker and less-labor intensive freeze drying method was developed for bulk materials. This freeze drying process proved to be able to produce free-flowing powder from a single vessel. Known as active freeze drying (AFD), the new process used continuous motion to improve mass transfer and also has cut processing time, while also eliminating the need to transfer to and from drying trays and downstream size reduction devices.