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What are the main problems in the production of apple juice concentrate - from a practical point of view?

Apple juice concentrate is prepared from clean, sound apples that have been washed and sorted prior to processing. Prior to juice extraction, apples are mashed and then depectinised to control viscosity. The juice undergoes filtration, assuring a product of brilliant clarity. The filtered depectinised juice is concentrated through low temperature vacuum concentration processes to provide the highest quality product available. The resulting 70° brix concentrate is immediately chilled and packaged as specified. The apple juice concentrate is processed according to good manufacturing practices.

One of the problems encountered relates to optimisation of the mashing process. Mashing of apples is normally performed in two types of equipment: a grater or a hammer mill. One of the critical aspects of this step is to obtain a proper consistency for economical juice extraction; if the pulp contains large pieces, the yield of juice will be low, but the juice will be relatively free from suspended solids. On the other hand, if the pulp is too finely divided, pressing will be difficult, and the juice will include a high content of suspended solids. It is therefore important to use the right equipment to ensure that the right consistency is obtained.

Another problem encountered is the laborious nature of the extraction step and low yields, coupled with large amounts of suspended solids in the juice. Traditionally, the techniques used are hydraulic pressing, pneumatic pressing and continuous pressing (screw and belt). These techniques also have an additional problem with regard to the difficulty to clean and maintain the equipment and the limited opportunity for expansion. On the other hand, hazes that form in apple juice during storage are one of the more bothersome and expensive problems in the whole exercise of apple juice making. These hazes may be of biological and nonbiological origin. Biological hazes are not a real problem if sterilization is carried out properly. Tannin-protein type hazes, however, may pose a real problem, as tannins are in good supply in apple juices, and protein traces may appear through the use of enzymes and gelatin at the depectinisation stage. Tannin-protein particle growth may be avoided by using as little gelatin and enzyme as possible. Heating depectinised juice to 65-70°C and then cooling coagulates some protein that can be removed by filtration. The finer the final filtration, the fewer potential haze-forming particles will enter the bottle.

Optimisation of the process can be achieved by using centrifuges and a press aid during extraction to increase the yield, and the use of membrane processes, specifically ultrafiltration for clarification, in order to achieve increased juice recovery, enhanced product quality, cold sterilisation and minimum waste production