MEMBRANE FILTRATION AND FLASH PASTEURIZATION ALTER VOLATILE AND PHENOLIC PROFILES IN CRAFT BEER: CHEMICAL BASIS FOR SENSORY STABILITY

Membrane filtration and flash pasteurization ensure microbiological stability in craft beer, yet thermal treatment alters aroma perception in a style-dependent manner, with India Pale Ale (IPA) showing greater sensory discrimination and Red Ale exhibiting reduced aroma liking. The chemical mechanisms underlying these differences remain uncharacterized, limiting brewers' ability to calibrate stabilization without compromising sensory identity. This study quantified volatile and phenolic constituents altered by membrane filtration and flash pasteurization in IPA and Red Ale, establishing analytical markers consistent with sensory outcomes. Three independent batches (n = 3 per style) were bottled after membrane filtration (0.45 μm) and flash pasteurization (65 °C, 20 s; 15 PU), then stored at 4 °C and 20 °C for 120 days. Volatiles were extracted by HS-SPME (DVB/CAR/PDMS 50/30 μm fiber; 40 °C, 30 min equilibration, 40 min extraction) and analyzed by GC-MS (Agilent 7890B/5977A; DB-WAX column, 60 m × 0.25 mm × 0.25 μm) for esters, higher alcohols, and hop-derived terpenes. Total phenolic content (TPC; Folin-Ciocalteu, mg GAE/L) and antioxidant capacity (DPPH, ABTS) were determined spectrophotometrically; data were analyzed by two-way ANOVA, Tukey's test (p < 0.05), and PCA (Statistica 13.0). Pasteurization reduced hop-derived terpenes in IPA (linalool: −18.4%, p < 0.01; geraniol: −21.7%, p < 0.01), while ester and higher alcohol variation remained below 8% (p > 0.05). Red Ale showed a 15.6% decline in total volatile intensity, 12.3% TPC reduction (187.4 ± 6.2 to 164.3 ± 5.8 mg GAE/L, p < 0.01), and a 9.8% decrease in DPPH scavenging (p < 0.05), versus 6.2% phenolic reduction in IPA (142.1 ± 4.9 to 133.3 ± 5.1 mg GAE/L, p < 0.05). After 120 days, losses intensified only in Red Ale at 20 °C (additional 7.4% TPC decline, p < 0.01); refrigerated samples remained stable (< 3% variation). PCA discriminated stabilized from non-stabilized samples (68.7% variance), driven by terpene and phenolic descriptors. The pronounced lability of monoterpenes relative to phenolic antioxidants reflects distinct degradation pathways: terpenes undergo thermal volatilization and oxidation, notably β-myrcene and linalool, whereas phenolics undergo slower oxidative polymerization, explaining the higher sensory discrimination in IPA, consistent with terpene degradation reported in pasteurized hoppy beers. In Red Ale, concurrent phenolic and volatile losses reduced aroma complexity, explaining decreased liking, while the greater TPC decline reflects higher initial phenolic load and matrix interactions such as melanoidins from specialty malts. Limitations include the absence of oxygen quantification and a single pasteurization intensity; future work should assess variable PU levels and headspace oxygen. These findings provide a chemical rationale linking terpene and phenolic degradation to style-dependent sensory outcomes, offering brewers quantitative thresholds to calibrate pasteurization intensity by style and support protocols preserving safety and sensory identity.