It is type of preservation technique basically used for heat sensitive products like fruits, meat stuff or pharmaceuticals. The basic process involves freezing material below triple point. This is temperature at which solid, liquid and gases can coexist. In this process 95% of water will remove in order to increase the shelf life of food product
- In 1906 Arsened Arsonval and Fredric Bordas(assistant) had invented the process of freeze drying
- At the laboratory of biophysics of college de France in Paris
- Later in 1911 Downy Harris and Shackle established the lyophilization process
- Application of freeze drying process in food industry has started after 2nd world war
Basic science and associated benefit
Freeze drying is also termed as lyophilization which is low temperature dehydration process which involves freezing the product, lowering pressure then removing ice by sublimation.
It involves three basic steps i.e. 1. Freezing 2. Primary drying 3. Secondary drying
In freezing phase it is very important to first freeze the food product in order to prevent formation of large crystals. Pressure is lowered through the application of high vacuum and this step may takes place about several hours to 2 days
In primary drying, temperature is little lowered as compare to freezing phase. Vapour pressure difference is the driving force between the evaporating surface and the condenser.
In secondary drying unfrozen water molecules removes which is remaining after primary drying. In this phase temperature is raised so that water molecules get vapourized. Final freeze dried product typically contains 1-4% moisture. They are then packed in can or polybags.
Basic elements of freeze drying are: Refrigeration system
Each system has its own specific function. Refrigeration system is used to cool the shelves and freeze the product. In vacuum system vacuum pump is connected to condenser. Control system the temperature and pressure gradient. Food is spread on trays, heat is supplied through conduction. The condenser attracts the vapours being sublimed off the product and condenses them back into solid form. Both continuous and batch freeze dryers are available commercially.
1. It is commonly used for coffee, fruit, juice, vegetables, herbs, food flavorings, eggs and dairy.
2. These product can be used for camping, space exploration, and military person
3. Larger sized product need to be cut into smaller pieces prior to freeze drying.
- It increases the shelf life of food product.
- It also decreases the microbial load of food product.
- Loss of volatile material is less.
- Sterility can be maintained.
- Material can be dried in its final container such as single dose or multiple dose vials
- Equipment and running costs are high.
- The period of drying is high and the time cannot be shortened.