Brewing Beyond Hot Water - Instrumental and Sensory Impacts of Non-Thermal Extraction on Commercial Teas

Non-thermal extraction technologies are increasingly explored to produce premium ready-to-drink tea infusions with high sensory quality and minimal colour degradation. This study evaluated three extraction methods - conventional hot infusion (control), cold extraction, and high-pressure processing (HPP) extraction - applied to four commercial teas representing different oxidation/fermentation levels and countries of origin: Bancha (Green, Japan), Tung Ting (Light Oolong, Taiwan), Black Dragon (Dark Oolong, China), and Darjeeling (Black, India). For each tea-extraction combination, colour parameters (L*, a*, b*, C*, h*), browning index, turbidity, Brix, pH, and conductivity were measured (n = 3). For the sensory profiling, key typical attributes (honey, floral, smoky, bitterness, and astringency) were first selected by a panel of 3 trained assessors. Subsequently, 22 experienced food technology assessors (professors, researchers, and postgraduate students) evaluated the samples. Sensory assessments included a preliminary consumer liking test (using a 9-point hedonic scale for analysis) and a Difference from Control (DFC) test relative to the hot control using a bipolar relative scale from -5 (much weaker than control) to +5 (much stronger than control). Univariate ANOVA with Tukey HSD post-hoc tests showed that extraction technology significantly (p < 0.001) affected lightness (L*), colour difference from the hot control (ΔE), turbidity, and browning index in all teas. HPP consistently preserved or improved lightness (L*) compared to the hot control (Bancha: HPP = 94.82 vs. hot = 92.13; Tung Ting: HPP = 96.40 vs. hot = 95.24), whereas cold extraction significantly reduced lightness in darker teas. HPP also significantly reduced turbidity compared to the hot control in Bancha (165 vs. 1005 NTU) and Black Dragon (160 vs. 991 NTU), and consistently yielded the lowest browning index across all teas (Bancha: HPP = 0.40, hot = 0.61, cold = 0.93). Colour difference (ΔE) remained minimal for HPP (ΔE of 1.5–6.5) but was pronounced for cold extraction (ΔE of 9.1–30.8). Principal Component Analysis (PCA) integrating instrumental variables and liking scores explained 79.8% of the total variance (PC1: 59.2%, PC2: 20.6%). Liking was strongly correlated with lighter, less turbid, lower Brix, and lower-browning index infusions. DFC profiling showed that cold extraction increased specific sensory notes (floral, honey, or smoky) but also astringency, whereas HPP infusions closely matched the control profile, frequently with reduced bitterness or astringency. These results support the potential of HPP as a promising alternative brewing technology for premium ready-to-drink teas.