84 Processed Apple Products. Table 4-1. Materials Causing .... zation of insoluble pectin was the first important step in the course of clarification. Experiments ...
4 Clarification of Apple Juice Arun Kilara and Jerome P. Van Buren
Consumer preference for a totally clear, shining apple juice has made clarified apple juice much more popular than unclarified natural apple juice. The production of clear apple juice requires the removal of suspended material and prevention of the development of turbidity after juice bottling. Freshly pressed juice contains suspended solids that are deliberately precipitated prior to filtration. This precipitation step is' called clarification. Other measures often are taken to remove soluble materials that have the potential to form after-bottling hazes. These measures are often called fining. Fining methods, which can remove haze particles as well as soluble materials, are discussed in chapter 5. Table 4-1 lists materials that may cause turbidity in apple juice and their relative sizes. Apple juice from a press or extractor contains not only discrete solid particles but also unstable compounds that can be coagulated by heat or by enzyme action. Depending on pressing or extraction conditions, the amount of solids in the juice may vary from 0.5 to 8% as determined by centrifuge test. The largest solids are normally removed as the juice comes from the press by rotating or vibrating stainless-steel screens. In some installations a continuous self-cleaning centrifuge is used for this purpose.
SUBSTRATES CONTRIBUTING TO TURBIDITY Pectic (Greek-congealing) substances are a group of complex colloidal plant carbohydrates made up primarily of (1,4)-a-D-polygalacturonic acid (fig. 4-1). This polygalacturonic acid exists in widely varying states ofmethoxylation and neutralization. Pectic acid is almost pure, colloidal polygalacturonic acid practically free from methyl groups. 83
