Combination of methods to understand lactose caking mechanisms

Caking is a recurrent problem in various industries, which occurs during the production, storage or transport of powders, and leads to lower production rates and decreased product quality. Given the significant economic loss associated with this adverse evolution, there is still much ongoing research on the subject. The complexity of this topic lies in the many parameters which can influence the caking phenomenon in an industrial context. Taking crystalline lactose powder as an example, the present study investigates how the washing and control of the size of the crystals along the production process influence the caking tendency of the final product under representative storage conditions. Alpha-lactose monohydrate powders with different levels of washing were produced at pilot scale, and sieved to separate 80, 160, 250, 355 and 500 µm fractions. Moisture sorption and amount of impurities of the different size fractions for varying washing degrees were assessed. Moreover the caking ability of the powder was measured with a ring shear tester. The amount of remaining impurities and the particle size distribution of the lactose powder were found to be critical to control in order to prevent enhanced moisture sorption and caking. Indeed it was shown that, for all washing grades investigated, the fines systematically contained more impurities and caked more strongly than the bigger particles. Industrials can use these findings to target the critical steps in the production process requiring optimisation to avoid caking in the finished product.