Characterizing Aroma Hop Aging and Evaluating HSI Reliability Through Commercial Inventory Examination

Hops undergo chemical changes during storage that affect both bitterness and aroma, critical for beer consistency. While the Hop Storage Index (HSI) effectively tracks bitter acids degradation, many people suspect that it may not be effective for aromatic changes, but this suspicion remains poorly documented. This study investigates the impact of post-pelleting/packaging aging and storage on aromatic hop quality by analyzing chemical, biochemical, and sensory attributes to establish a baseline understanding of aroma hop aging in conventional storage.

Three widely used aroma/dual-purpose hop varieties—Cascade, Citra®, and Centennial—were selected, with three different commercial pelleting lots per year over a period of four to five harvest years. Oxygen and CO₂ levels in packaging were recorded at the time of analysis, followed by chemical (alpha acids, HSI, oil content, oil composition, and free thiol analysis), biochemical (hop creep assay), and hop grind sensory analyses. Single-hop IPAs were brewed using fresh (2023) and aged (2018–2020) samples, with triangle tests conducted on the final beers to assess perceptible differences.

While oxygen exposure in packaging was unequivocally detrimental to hop quality, results from properly stored hops indicate variety-dependent aging effects. Citra maintained stable essential oil content, composition, and sensory attributes over four years of cold storage. Centennial exhibited minimal chemical changes but showed sensory differences over time. Cascade displayed significant aging effects, with statistical correlations between age and changes in volatile compounds and resins, as well as clear sensory distinctions in older samples. HSI failed to reflect aromatic degradation, particularly in slightly oxidized samples, underscoring the need for a new metric to assess aroma hop freshness vs degradation. While beers brewed with older Citra remained indistinguishable from fresh counterparts, those made with aged Cascade and Centennial showed noticeable differences.