Instant coffee powder is highly sensitive to environmental humidity, which can significantly affect its quality during storage. The objective of this study was to evaluate the storage stability of instant coffee by assessing the moisture uptake and monitoring the evolution of key quality indicators under different environmental relative humidity (ERH) conditions. To this purpose, instant coffee was removed from its original packaging and stored at 11, 32, and 65% relative humidity (ERH) at 20 °C. Quality parameters related to both the powder (visual appearance and solubilization time) and the resulting brew (pH) were monitored over time. The coffee stored at 11% ERH demonstrated stability throughout the observation period. Storage at 32% ERH resulted in short-term powder stability, but a notable pH decline after six months. At 65% ERH, critical moisture levels were exceeded within one week, resulting in rapid visual degradation, impaired solubilization, and reduced brew quality within three months. The acquired findings on the behavior of a dry food powder under various storage conditions are particularly relevant in the context of the increasing application of compostable packaging with low moisture barriers, in conjunction with the need to manage the secondary shelf life of dry food powders whose use is often parceled.
