Identification of suitable plate geometry and gap size for rheological characterization of grape juice

This study aimed to identify the optimum plate geometry and gap size for measuring the rheological properties of grape juice and to validate the literature's suggested dimensional correlation that the gap should be at least ten times larger than the particle diameter. Gaps from 1.3 to 2.5 mm were tested with flat plate geometry. The third shear flow curve was analyzed to minimize thixotropic effects. The best gap was compared to the juice’s particle size, measured by laser diffraction. Data were fitted to Newtonian, Power-Law, and Herschel-Bulkley models, with the quality of fits assessed by R2, Sum of Squares of Errors (SSE) and Root Mean Square Error (RMSE). Gaps of 1.75 mm and 2.0 mm with smooth plates and a 2.0 mm gap with a rough plate showed typical juice behavior. The 1.75 mm gap, 10.93 times larger than the average particle size, met the recommended ratio. The juice has pseudoplastic behavior and can be predicted by Herschel-Bulkley model (R2 = 0.998, SSE = 9.63×10-2, RMSE = 0.031). The 1.75 mm gap with smooth geometry was ideal, reducing sample requirements and costs.