Relationship between in-line viscosity and Bostwick measurement during ketchup production

The Bostwick consistometer remains an integral part of assessing the consistency of tomato products in the factory. This work addresses the blending of tomato pastes, packed at different Bostwick readings, for use in tomato ketchup production. The objective of this study was to correlate in-line viscosity measurements of 12 degrees Bx tomato concentrates to final product quality. Five blends of tomato concentrate were prepared by blending 2 pastes and diluting the mixture to a soluble solids level of 12 degrees Bx. In-line viscometry measurements at process temperature were made using magnetic resonance viscometry. The resulting Herschel-Bulkley parameters were used to evaluate an apparent viscosity at a characteristic shear rate. The apparent viscosity and Bostwick measurement for the blends were correlated based on a gravity current flow analysis, yielding a coefficient of determination of over 0.99. Ketchup was made from the tomato concentrate blends at 3 levels of natural tomato soluble solids (NTSS). The ketchup Bostwick measurement was then correlated to the ratio of (eta/rho)(-1/5) of the 12 degrees Bx tomato concentrate yielding coefficients of determination of 0.97, 0.97, and 0.91 for NTSS levels of 6%, 7%, and 7.8%, respectively. This study demonstrates that final product quality can be predicted from in-line viscosity measurements of an intermediate product.