Stick-slip behavior of dairy powders: Temperature effects

Many powders show a characteristic behavior when sheared, known as stick-slip. For such powders, when sheared under a normal load, once the peak shear point has been reached, the shear stress values start oscillating. The causes of stick-slip at particle level and the factors affecting this behavior are not well understood. In the present work, the stick-slip behavior of three dairy powders, a skim milk powder, a whole milk powder and a cream powder, has been studied with an annular shear cell with the aim of identifying factors affecting the observed behavior. Tests were conducted in a constant temperature room at 25 °C, 30 °C and 37 °C and in each case at normal loads of 9.5 kPa, 7.74 kPa, 4.37 kPa and 2.52 kPa. Both period and amplitude were dependent on normal stress for all powders at all temperatures tested.

Stick-slip behavior of skim milk powder in an annular shear cell; normal load, 9.5 kPa.The stick-slip behavior of a skim milk powder, a whole milk powder and a cream powder, has been investigated. Tests were conducted at 25 °C, 30 °C and 37 °C at normal loads of 9.5 kPa, 7.74 kPa, 4.37 kPa and 2.52 kPa. Both period and amplitude were dependent on normal stress for all powders at all temperatures tested.Figure optionsDownload as PowerPoint slideResearch highlights
► We tested a high fat, medium fat and a low fat dairy powder in an annular shear cell.
► Stick slip oscillation was observed in all three powders.
► Amplitude and period of stick slip oscillation were largest for the low-fat powder.
► Normal stress had a considerable impact on stick-slip motion.
► Fat content and its distribution in a particle influence amplitude and period.