Ventilated Room Temperature Drying as a Sustainable Alternative to Hot-Stove and Freeze-Drying Processes for Hops cv. Cascade

Hops are a fundamental component in beer production, primarily valued for their aroma, bitterness, and preservative qualities. Drying is essential to ensure their storability and usability throughout the year, but the method employed can significantly influence their chemical and sensory attributes. This study compared three hop-drying techniques—hot-stove drying (H), freeze-drying (F), and ventilated room temperature drying (VRT)—with respect to their impact on the quality of dried hops, focusing on bioactive compounds, antioxidant activity, and volatile profile. To achieve an 80% reduction in moisture content, both F and H required 48 hours at 40 °C and −52.4 °C (0.04 mBar), respectively. In contrast, VRT required five days at 25 °C under continuous airflow (1.2 m/s) with a humidity of 30%. 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). However, VRT preserved the highest total phenolic content (631.11 mg GAE/100 g dm), as determined by the Folin–Ciocalteu method, significantly outperforming H (348.48 mg GAE/100 g dm). Freeze-drying resulted in the best antioxidant activity (21.25 mmol TE/kg dm and 35.42 mmol TE/kg dm), measured via DPPH and ABTS assays, but its high operational cost limits its practical application. VRT showed the most significant increase in monoterpene hydrocarbons, while all treatments preserved key sesquiterpenes such as α-humulene, β-caryophyllene, and β-farnesene. Volatile compounds were extracted via solid-phase microextraction (SPME) and analyzed using GC-MS. Although browning was visually observed in VRT-dried hops, it was quantitatively confirmed through color variation analysis using the CIELab method. In conclusion, VRT appears to be a promising, low-cost technique to preserve the aromatic and antioxidant profile of hops, particularly suitable for small-scale brewers. Future research should further investigate the effects of these drying methods on beer quality and fermentation performance.