Chemical Quality and Characterization of Essential Oils in Postharvest Hop cv. Cascade: Ventilated Room Temperature as a Sustainable Alternative to Hot-Stove and Freeze-Drying Processes

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Abstract
Hop is a key ingredient in beer production, and drying it allows it to be stored before use. Unfortunately, postharvest drying techniques can negatively affect hop quality. In this study, we compared drying using a hot stove (H), freeze-drying (F), and ventilated at room temperature (VRT) drying, focusing on the chemical quality and essential oil composition. To achieve 80% water removal, F and H took two days, while VRT took five days. F and H preserved a high content of total chlorophyll (F 81.89 g/kg dm; H 82.70 g/kg dm) and carotenoids (F 54.02 g/kg dm; H 54.71 g/kg dm). The hop storage index (HSI) increased with all drying techniques, but especially in F and H. The lowest amount of polyphenols was found in the H sample (348.48 g/kg dm), while the highest content was found in VRT (631.11 g/kg dm). Freeze-drying gave the best results, especially in relation to the amount of polyphenols and antioxidant power of the product. Regarding essential oils, in the class of sesquiterpene hydrocarbons, we found α-humulene (F 24.0%; VRT 24.7%; H 25.6%), β-caryophyllene (F 10.5%; VRT 9.4%; H 11.1%), and β-farnesene (F 6.8%; VRT 6.0%; H 7.4%). The total monoterpene hydrocarbon amount increased in the VRT sample. Thus, freeze-drying emerges as an alternative technique to the hot stove; however, the cost is high. Instead, drying at ventilated room temperature represents a sustainable and valid technique for preserving the aromatic characteristics and polyphenols of the product.

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