GRINDING SPRAY‐DRIED MILK POWDER NEAR the GLASS TRANSITION TEMPERATURE

Abstract

ABSTRACTThe fine grinding of chocolate is typically accomplished on five‐roll mills. Chocolate manufacturers consider milk powder, a component of milk chocolate, difficult to grind. Spray‐dried milk powders comprise a glassy lactose matrix in which fat globules, air vacuoles and protein are entrapped. the glassy‐rubbery transition in commercial milk powders usually lies between 60–70C, depending on the moisture content. A mixture of 60% wt/wt commercial whole milk powder, Tg∼ 60C, and 40% wt/wt cocoa butter was ground in a three‐roll refiner at temperatures of 40, 50, 60, 70 and 75C. Below Tg the particles exhibited brittle fracture, while above Tg plastic deformation was evident and particles became highly asymmetric. the amount of fat liberated from the lactose matrix, so‐called free fat, particle density, and mean particle size increased with grinding temperature. However, the Casson yield value and plastic viscosity of finished “white chocolate” coatings, manufactured to a constant free fat content, increased with grinding temperature, suggesting an influence of particle shape on flow behavior.