Evaluation of the stability of hop pellets subjected to different storage conditions during three years

It is common knowledge that the composition of hops secondary metabolites depends on several factors, among which the storage conditions. In recent years, many studies have been conducted to evaluate changes in the chemical composition of hop products in response to different storage temperatures both in aerobic and anaerobic environments. However, little knowledge exists regarding the storage of hop pellets under modified atmosphere for a very long period of time. The aim of this study is to evaluate the effect on hop quality parameters of different storage conditions on U.S. hop cultivar pellets (Chinook and Nugget) in a three-year trial. Storage in modified atmosphere (atmosphere saturated with 70% nitrogen (N₂) and 30% carbon dioxide (CO₂) and vacuum storage were tested at two different temperatures, 4 °C and 10 °C. In order to establish the best storage condition, the bitter acids content (HPLC-UV method), the essential oil content (steam distillation method) and the essential oil profile (GC-MS method) were determined and characterised at 0, 6, 12 and 36 months. No statistical differences were observed between samples stored under different atmospheres, while significant differences were highlighted as a result of the storage temperature, e.g. the alpha acids content at 4 °C was significantly higher (P = 0.002). The two hop cultivars showed different behaviours in the storage trial, suggesting that high alpha hop varieties, like Nugget, could be stored even at higher temperatures.