A recurring problem with juice concentrates is that, on reconstitution of the original strength juice, there is a loss in consistency (Marsh et al 1978) . This is reflected in a lower product yield for products produced from concentrate as compared to products prepared directly from the original juice. It is commonly held that this loss in consistency is in part due to the thermal effects of the concentration/ evaporation process (Ilker and Szczesniak, 1990) , or the mechanical changes induced

more »

... y the shear effects during fluid flow within the process ( Mannheim and Koperlan, 1964; Berovsky et al, 1995). This paper demonstrates that a further, important, cause is irreversible molecular associations induced by the existence of high solute concentrations in the final concentrate. Using tomato juice concentrates we demonstrate that the particle sizes of the dispersed hydrocolloid materials is reduced as a consequence of being having the water concentration in the system reduced, then returned to the original level. This size change, corresponding to an approximately 10% decrease in phase volume under the conditions investigated, correlates well with the changed flow rheology characterization of the initial and final system. Further confirmation of the importance of concentration induced aggregation as a source of consistency loss is provided by comparing the loss accompanying a tradition evaporation-redilution process with the change in consistency accompanying a freeze thaw cycle. There is an important correlation between the changes in consistency accompanying these very different processes. The referenced patent (Reid 2004) applies this correlation to allow for prediction of potential consistency loss in evaporative paste production by merely freezing some of the original juice material, and evaluating the change in consistency of the thawed material in contrast to the original.. Keywords: