Technology
THE FREEZE DRYING PROCESS
Freezing
The fruits or vegetables are frozen at very low temperatures (–50 until –80 degrees Celsius). The quicker the freezing process the smaller ice crystals are formed from water which is in the product. The goal is to freeze the product quickly and uniformly to minimize damage to its structure and preserve its quality.
Primary Drying (Sublimation)
The drying process is done in two steps. The first step is quite slow and takes a couple of days. Under reduced air pressure most of the ice crystals are removed by sublimation, this means that the ice turns directly into water vapor. This takes place at temperatures that are typically several tens of degrees below freezing. The low temperature does make the sublimation take longer but it also ensures optimal preservation of taste and texture.
Secondary Drying (Desorption)
Finally, the temperature of the freeze-drying chamber is slightly increased, and the remaining bound water within the product is removed through a process called desorption. The structure of the product is already established.
The purpose of the secondary drying stage is to ensure that all residual moisture is eliminated, further enhancing the stability and shelf life of the freeze dried product.
- Long shelf life (18-24 months after production)
- Preserves up to 98% of all nutrients (vitamins, minerals, …)
- Pure (clean label) – no additives
- Concentrated and intense natural flavour (equivalent of several portions of fresh fruit)
- Freeze dried products retain their shape and colour
- Crispy texture (pieces)
Applications
The highest added value is obtained in dry end products (bakery, chocolate, breakfast cereals, supplements, confectionary, …)
Comparative table freeze drying versus conventional drying
| Product quality | Freeze drying | Conventional drying |
|---|---|---|
| Form of wet material to be dried | Whole, liquids, pieces, powders | Pieces |
| Dry shape and form | Maintained | Shriveled |
| Appearance | Nearly same | Shriveled |
| Color | Maintained | Faded |
| Rehydration | Fast | Slow |
| Heat exposure | 0-150°C | 200-300°C |
| Oxygen exposure | Very low | High |
| Retained volatiles | Excellent | Poor |
Other drying
For certain specific products that are, for example, technically difficult to freeze-dry, Frubero can also offer alternatives with other drying techniques such as air drying and spray drying.
Spray drying
Is a process used to transform a liquid or slurry into dry powder or granules. It involves spraying the liquid material into a hot air stream, causing rapid evaporation of the liquid, leaving the dried particles as free-flowing powder, the particle size is below 500 microns.
Applications
Drinks, bakery, dairy applications (ice cream, milk, …), …
Air drying (belt dryer)
With a continuous conveyor dryer in the food industry is based on the concept of continuous drying using a conveyor system. The dryer consists of a perforated belt that moves through a series of heating chambers. As the belt moves, the food product is spread evenly on its surface, allowing for uniform heat transfer. In contrast to sun drying, industrial air drying with belt dryers is more controllable.
Frubero offers a limited range of air dried products in case where freeze dried is technically not possible or does not have the appropriate functionality (for example solubility in drinks).
Applications
Visual and organoleptic less critical applications (muesli, …)
