Storage and transport conditions, including temperature and humidity, can have a wide range of effects on the physical properties of powders such as loss of pharmaceutical potency, particle attrition and powder caking. Powder caking is the undesirable process of a particles forming agglomerates, which can accumulate to form “cakes”. Industrial methods for determining the conditions when powder caking can occur are often time-consuming, require large sample volumes and provide little scientific insight of the agglomeration mechanism. Also, current experimental techniques rarely represent the “real-world conditions” and may provide inaccurate data when compared to the actual storage and transport lifetime of the powder sample. A novel characterization method has been developed for assessing the role of humidity in powder caking based on an in-situ measurements of powder flow rheology. Concurrently the sample is exposed to the selected environment humidity whilst powder flow properties are determined. This new method is much faster than current industry standards and correlates well to other common methods used for caking characterisation. The new technique uses a modified FT4 powder rheometer, and the data obtained correlates with common experimental methods used in solids handling and is easily reproducible due to its modular design. Among other parameters, this method measures flowability energy, as a function of relative humidity. Powder flow energy is a measure for a powder’s resistance to flow and reflects interparticle adhesion processes. This new measurement protocol is designed to assess the relative humidity conditions where the onset of caking occurs. The flexibility of the setup has the potential to be utilized more broadly for determining the moisture-induced changes in powder rheology for example in wet granulation, drying and mixing processes. This new method of powder flow characterization can be used for a wide range of powders differing in crystallinity, morphology, particle size and chemical structure.