Improving the utilization of summer tea leaves through steam explosion technology: flavor transformation and cold-brewing feasibility

Summer tea leaves, characterized by thick cell walls, low aroma, and strong bitterness, are generally considered unsuitable for high-quality tea production. This study investigated the potential of steam explosion technology (SET), which exposes the leaves to high-pressure steam followed by rapid depressurization, for processing these leaves. Under optimal condition (0.6 MPa, 180 s), SET led to significant cell wall disruption, enhancing the release of polyphenols. Sensory analysis showed that steam-exploded tea achieved a flavor profile comparable to white tea made from spring leaves. GC–MS analysis revealed markedly increased extraction of desirable volatile compounds. UPLC-QTOF-MS confirmed that reductions in flavanols, phenolic acids, and caffeine (by up to 15.61 % ∼ 35.28 %) contributed directly to reduced bitterness. Furthermore, steam-exploded tea was suitable for cold-water brewing, achieving high extraction rates of key compounds compared to hot-water brewed tea. These findings highlight SET as a sustainable solution for enhancing summer tea quality and usability.