Estimation of clotting and cutting times in sheep cheese manufacture using NIR light backscatter

Abstract

During sheep cheese manufacturing, the time determination for such important steps as clotting and cutting time relies on the experience of the cheese maker or, alternatively, on predetermined reaction times. However, efficient control of coagulation requires a rigorous, objective, inline method to select the optimum time to proceed with clotting and cutting time. Therefore, a near-infrared (NIR) light backscatter fiber optic sensor was implemented in order to monitor coagulation of sheep milk and assess the possibility of estimating both clotting and cutting times during the manufacture of sheep’s cheese. A randomized block experiment with three replications was designed to determine optical, rheological, and visual coagulation parameters in sheep milk using four enzyme concentrations. The optical response of the sheep milk was found to be greater than in goat milk (15–20%) but lower than cow milk (30–50%). The standard error for the optical parameters during the coagulation of sheep milk was lower than those observed for the visual parameters. Optical variables were strongly correlated with both visually and rheologically defined coagulation parameters. Rheologically and visually determined clotting and cutting times were successfully predicted using only one optical parameter. Our results suggest that optical parameters generated from the NIR light backscatter profile adequately respond to the kinetic changes induced by varying the concentration of enzyme and that prediction of rheologically determined cutting time using NIR light backscatter is more precise than prediction of visually determined cutting time, i.e., ∼50% lower SEP.