Freeze concentration is a processing technique used to extract water from a sample without losing valuable aromatics. One very common use of this method is in the handling of fruit juices to produce concentrates with an intense flavor. The concentrate can be used to make new products, or frozen and mixed with water later to produce a juice with a fresh taste. Food processing facilities may maintain process equipment for freeze concentration if they handle high volumes of fruit juices.
This process relies on the fact that solutions have a lower freezing point than plain water. Historically, freeze concentration could be accomplished by putting juice into a freezing environment and allowing it to sit overnight. A crust of ice would form on the surface, with a layer of liquid concentrate below. Alternatively, juices frozen solid could be allowed to melt into a container to catch the fluid. The juice would pour off first, leaving ice behind.
In commercial freeze concentration, these batch methods are not always efficient. Instead, companies typically use a continuous process. The material is passed through a refrigeration unit to chill it, promoting the formation of ice crystals. These can be filtered out as the liquid moves through the unit, leaving a concentrate behind. Not heating the mixture allows it to retain aromatics and flavors, so it will have an intense, rich taste.
Finished concentrates can be used in a number of different ways. Many have a long shelf life once frozen, and can be stored for use in a variety of products. They can be used to produce packaged juices, as well as being used as sweeteners for products like desserts and candies. Concentrated fruit juices tend to be extremely sweet. Storing concentrates allows companies to cut down on the volume of storage while preserving the most useful component of fruit juices.
It’s possible to use freeze concentration in processing at home, with the batch method discussed above. The solution should not be disturbed while it starts to freeze down, as this can cause ice crystals to distribute in the mixture, which will result in a watery concentrate. The finished concentrate may be stored in frozen form for future use or added to cooking projects like jams.
One advantage to this method is that it can limit bacterial growth. Freezing can inhibit infectious organisms and keeps concentrates safe. As long as they are handled carefully at room temperature, they shouldn’t have the ability to cause food borne illness.