Development of a scraper-rheometer for food applications: Rheological calibration

In order to follow the rheology of food products during heat processes in scraped surface heat exchangers, an original device was developed. It consists of a cylindrical viscometer equipped with scraper blades and called “scraper-rheometer”. An experimental rheological calibration of this system was performed by using several calibrated Newtonian fluids (silicon oils) and non-Newtonian shear thinning fluids (xanthan and CMC solutions) in laminar and isothermal conditions. The Couette analogy was used with calibrated Newtonian fluids in order to calculate an outer equivalent radius of the cup. It was then possible to determine the viscosity of a Newtonian sucrose solution and the apparent viscosity of shear thinning xanthan and CMC solutions in scraper-rheometer. Measured viscosities in this atypical geometry were in good agreement with reported literature values or with measurements performed with a classical geometry. These results indicate that the scraper-rheometer is a promising tool to follow rheology of most food products subjected to heat transfer and shear rates and showing Newtonian or shear thinning behavior such as ice cream, butter or chocolate.