Abstract
Butter possesses a remarkable non-Newtonian character in its rheological properties. A quantitative study of the viscosity and yield value have been performed under various conditions of working time at a constant temperature of 20°C. The apparatus employed in the measurement involve a cone-plate viscometer and a parallel plate plastometer.
The viscosity and yield value decrease remarkably when the specimen is subjected to the kneading on the roll mill, but they recover gradually to their original values when the specimen is subjected to setting for a long time. This phenomenon may be considered as a kind of thixotropy.
The volume dilatometry of the specimen was also carried out continuously for a setting period of two months. From the comparison of results, the magnitude of viscosity or yield value of butter could be successfully connected to the degree of crystallization of fat in butter which had been evaluated from the specific volume of the specimen. The origin of the thixotropic softening of butter should be sought for, therefore, in the mechanism of rupture and formation of the three dimensional network of crystals in the specimen.
