Driven by the growth in the infant formula market, lactose production is increasing worldwide, and at the same time the requirements for the product quality are becoming stricter. Caking, or the unwanted agglomeration of lactose powder particles, is synonym of poor quality for the customers and should therefore be prevented to avoid significant economic loss. This PhD project aimed at understanding the caking mechanisms in lactose powder in order to establish means to limit caking. The process – product relationship has been in focus in order to find and control the parameters that determine the caking tendency of the product. Samples from pilot production were analyzed for different physicochemical characteristics (impurity content, moisture sorption, particle size) and caking behavior. Impurities (i.e. non-lactose components) were shown to increase moisture sorption and caking. The particle size distribution of the powder also exhibited a large effect on caking. Indeed, smaller particles were characterized by enhanced moisture sorption and stronger caking, which were explained by a larger impurity content and surface area. In addition, for a similar mean particle size, a broader distribution span led to stronger caking because of the multiplication of contact points. Analyses on the commercial powder confirmed these results and revealed the instability of the water activity during storage of the powder after drying, which was linked to caking in the lactose bags. This PhD project also addressed an essential need in the dairy industry, i.e. the development of an accelerated caking test. Samples from different production sites were discriminated in terms of caking in less than a day, using appropriate test conditions (50°C and 60% RH). A similar test implemented at all sites would highlight batches with a high caking tendency before shipment to the customers. The better understanding of the caking mechanisms provided by this PhD work enables industrials to target the critical processing steps requiring optimization to avoid caking in the finished product.