Effect of solids concentration on the rheology of labneh (concentrated yogurt) produced from sheep milk

The effect of solids concentration on the apparent viscosity of labneh made from sheep milk has been investigated using a rotary viscometer. Sheep labneh was manufactured following the traditional method by using cloth bags. Apparent viscosity of labneh with four different solids concentration was studied as a function of the shear rate. It is found that sheep labneh with different solids concentration exhibits shear thinning and thixotropic behavior. The power law model was found to fit the apparent viscosity - shear rate experimental data, satisfactorily. Both the consistency coefficient and the flow behavior index were correlated as a function of solids concentration. The predicted apparent viscosity showed an absolute average error of less than 5%. Time-dependent viscosity measurements were performed at four different shear rates. Using the structural kinetic approach, a 1.5-order kinetic model was found best for correlating the experimental data. Completely destructed labneh, after 4-h preshearing, was also studied as function of shear rate. Comparison between labneh made from cow milk and sheep milk was performed, whenever data were available.