練圧によるバターの粘度の変化

抄録

The variation of viscosity, rigidity and yield value of butter due to working has been measured. The working of butter has been performed by kneading the specimen in a duplicate roller which is composed of two cylinders with the same diameter and rotating in the opposite direction.
The diameter of cylinder was 7.6cm and the gap between two cylinders were varied in three steps i. e. 0.55mm, 1.65mm and 4.05mm. The temperature at working was 25°C to 27°C. The small specimen of butter was taken up from the roller at a fixed time interval during working and the viscosity and rigidity of the specimen were measured by a vibration-plate viscometer. The viscosity and yield value of the worked specimen after setting at constant temperature of 16°C for 20 hours, 8 days and 10 days respectively have been measured by a parallel plate plastometer. The formula used in the calculation was that derived by Oka et al.
Both the viscosity and rigidity of butter decrease rapidly with the amount of working and approach to the saturated values which are determined by the distance of gap between two cylinders. The smaller gap produced the more amount of working, hence the lower saturated values of viscosity and rigidity were obtained. The viscosity and yield value measured after setting for 20 hours decreased also with the working time. The remarkable recovery of these values were observed after setting for 8 days or 10 days but the harder working resulted in the smaller recovery.
The effect of working is considered to destruct the network structure of fat crystals formed in butter as well as to decrease the size of each fat crystals. The recovery of the viscosity and yield value due to setting may be associated with the recrystallization of fat crystals.
A clear pattern of stripes parallel to the direction of rotation was observed in the butter during working. The number of peaks appearing in the pattern increases with the decrease of viscosity. Denoting D as the distance between two peaks of stripes, the following relation between D and the viscosity η has been determined experimentally, η=η₀e^-C/D-D₀, where η₀, C, D₀ are constants.