Haze and cloud in apple juices.

Turbidity in apple juice is desirable or undesirable, depending on whether the product fits within consumer expectations. Desirable opalescence is due to soluble pectin and insoluble pectin stabilized particles that show considerable stability. Blanching treatments enhance this stability by reducing particle size and character-solubilizing pectin, and possibly by the destruction of natural enzymes that may destabilize the cloud over time. Undesirable haze and sediments may arise in apple juice by several mechanisms, including starch (dextrin) retrogradation, protein phenol aggregation, phenol oxidation, crystallization of carbohydrate macromolecules extracted from cell walls, or difficulties during manufacture. The mechanisms of formation of each of these forms of haze are discussed and examples given form the literature. Where available, haze-sediment morphology by light and/or electron microscopy is documented and the possible role of recently developed "macerase" enzymes in haze/sediment formation discussed.