Both spray drying and freeze drying are widely used in many fields, but they are totally different methods. The main difference between them is the temperature difference. The spray drying is regularly carried out above 80℃, while the freeze drying is generally carried out at 0℃ in primary drying and below 20℃ during secondary drying. There are still other differences between them as well, which will be specifically concluded as follows:
Spray Drying VS. Freeze Drying
What is Spray Drying?
The spray drying is a type of drying technology, which can complete drying and granulation simultaneously. According to its technological requirements, the pressure, flow and the size of the nozzle of the feed pump can be regulated to obtain the required spherical particles according to a certain size proportion. It uses a special equipment to spray liquid material into a mist, which is dried by contacting with hot air.
The spray drying can create an instantaneous high temperature, vaporizing water rapidly. The drying effect is pretty good. Meanwhile, the particles of spray drying are more uniform and have a good dispersibility. But the nutrients and aroma of materials may be lost due to high temperature.
What is Freeze Drying?
The freeze drying is a new type of drying technology based on the principle of sublimation. The material containing water is froze at low-temperature. Then the ice sublimes and turns vapor directly. Water is lost when the vapor exhausts so the material turns dry. It can be used to carry out the dehydration process in order to preserve perishable material or make the material more convenient for transport.
The freeze drying, also known as sublimation drying, is carried out under low temperature, which is especially suitable for heat-sensitive material. With a low operating temperature, the dried materials can maintain original chemical compositions and physical properties, such as loose structure and colloidal property. It is widely used for drying vegetables and fruits.
Is Spray Drying Better than Freeze Drying?
Compared to freeze drying, spray drying has a greater production potential, which is considered as a “continuous process”. But both of them are main drying methods used in many fields, and both of them have prominent advantages and disadvantages. We can’t simply say which is the best drying method. In the selection of drying methods, people should give consideration to the specific situations, materials and purposes.