SOLUBILIZATION AND RHEOLOGICAL BEHAVIOR OF RAISIN SUSPENSIONS

Solubilization of raisins is the first step in the production of raki or similar anise flavoured spirits. It is a two-phase process. Compone nts in direct contact with water dissolve at a constant rate in the fi rst phase. The rates of the first phase and final amounts of the solub ilized components increase with temperature and stirring rate and decr ease with particle size and volume of dissolving water. In the second phase of the solubilization phenomena, the driving force was the devia tion of the solubilized solids contents from the finally attainable va lue. A loose net-like structure was established in this phase; therefo re, the mass transfer rates were not affected by the actual size of th e particles. Apparent viscosities were close when measured at 100-300 rpm. Amounts of the solubilized solids and consequently apparent visco sity increased with temperature. The stirring rate did not have a larg e effect on the apparent viscosity at 175 and 312 rpm, but higher valu es were observed with 810 rpm towards the end of the process, possibly due to tangling of the disintegrated net-like structure of the partia lly solubilized raisins. Variation of the consistency index and the yi eld stress with time showed similar trends between 20 and 80-degrees-C , with the exception at 65-degrees-C, possibly due to sticky surface d evelopment. Consistent trends were also observed for variation of the consistency index and the yield stress with time when the only changin g experimental parameter was the stirring rate.