Fruit Juice Processing
The majority of fruit juice is made by reconstituting concentrated juice with water to a composition as similar to that of the original state. However, since records are not usually kept of the exact quality of the original juice, such reconstitution normally relates to an agreed trade standard. Reconstituted juices are often packed in aseptic long life containers such as TetraPaks.
There are many countries a growing market for fresh ‘single-strength’ juice made by squeezing fruit. Subjecting it into some processing, packaging it selling it within a cold chain distribution system. Such juice is usually referred to as ‘not from concentrate’ and will have a shelf life that varies from 1 or 2 weeks to 2 or 3 months.
In general terms, fruit are collected, sorted and washed, and then subjected to a type of mechanical compression appropriate to the fruit concerned. Although there are general fruit presses that can be used for more than one fruit type, fruit such as citrus, pineapple and stone fruits are usually processed in specially designed equipment.
Some fruit types (such as apples and pears) require mechanical treatment (milling) coupled with a biochemical process (involving enzymes) to break down the cellular structure and obtain best yields. It is possible to achieve almost total liquefaction by means of an appropriate enzyme cocktail.
Additionally, a diffusion or extraction process can be used to obtain best yields from certain fruits.
If juice is to be sold as ‘not from concentrate’ it is usually screened and pasteurized immediately after pressing – an operation with two main objectives. The first is to control the growth of spoilage micro-organisms that live on the fruit surface (mainly yeasts and moulds). The second is to destroy the pectolytic enzymes that occur naturally in fruit that would otherwise breakdown the cloudy nature of the juice. If, however, a clear juice is required, enzymes can be added to accelerate this natural process.
Juice for concentration is normally subjected to screening to remove cellular debris and then fed to a one or multistage evaporation process to remove most of the water and other volatile material. Evaporators today are highly efficient processing unit: up to nine stages are used, sometimes with the thermal recompression to obtain maximum efficiency. Increasingly, evaporators also recover the volatile aromatic substances that are partly responsible for giving fruit juice their sensory characteristics. The re-addition of such volatile is widely practiced at the point when concentrates are reconstituted into single strength juice.
After concentration, juices are normally held in storage until they are reconstituted. Some concentrated juices, particularly orange, require freezing at below -10 degree Celsius for effective preservation. Others, particularly apples, can be held at around 10-15 degree without risk of deterioration. The degree of concentration plays an important part in determining storage conditions: in the above examples, orange juice is normally concentrated to about 65 degree Brix and apple to 70 degree Brix.
Fruit Juice Processing
