Flow behaviour of low solids fresh cheeses

Abstract

SummaryA computerized, coaxial cylinder viscometer, controlled by a function synthesizer, was used to study the stress characteristics of acid fresh cheeses containing 7·5–8·5% protein and 0–20% fat in total solids, as a function of shearing time (0–3600 s) and of shear rate (0–4·5 s–1). For a given shear rate the stress diminished with time, following an exponential equation. The hypothetical final stress level (Sf for the shearing time t = ∞) represented about half its initial value (Si). For four cheese samples, the time required for the stress to become equal to Sf + (Sf – Sf)/e was 340–560 s. The stress-shear rate relation indicated shear thinning behaviour. The effect of shearing time showed that the material was thixotropic. The cheeses exhibited plastic flow. The initial and final stress levels were hyperbolic functions of the shear rate. Bingham final yield stress (for t = ∞) was 14–50 Pa. It was 15–25% higher for increasing than for decreasing shear rate. Bingham viscosity (for t = ∞) was between 2 and 6 Pa s. It was 10–20% higher for decreasing shear rate. The initial level of Bingham viscosity was ˜ 30% higher than its final value.