Bioscience Evidence 2026, Vol.16, No.4, 235-248 http://bioscipublisher.com/index.php/be 236 studies on microbial fermentation, aroma improvement in black tea, light-assisted withering, and diversified tea processing have provided practical approaches for increasing the utilization value of summer and autumn teas. These findings offer useful references for improving the year-round utilization of fresh tea leaves harvested in different seasons. 2 Seasonal Variation in Tea Quality Formation 2.1 Quality characteristics of spring tea Spring tea is generally regarded as the highest-quality tea of the year. It is characterized by a fresh taste, natural sweetness, clean aroma, and well-balanced flavor. Whether for green tea, white tea, or black tea, spring-harvested leaves usually produce better sensory quality than summer or autumn teas. Ye et al. (2022) compared black teas produced from the large-leaf cultivars Yinghong 9 and Huangyu and found that spring tea achieved the highest scores for aroma, taste, liquor color, and overall sensory quality. Studies on white tea and Xinyang Maojian also showed that spring tea had a fresher aroma, stronger umami taste, and higher consumer acceptance than teas harvested in later seasons (Yin et al., 2022). Even within the spring season, early spring tea is often superior to late spring tea, indicating that the quality advantage of spring tea gradually changes as temperatures rise and new shoots develop. The high quality of spring tea is mainly associated with the accumulation of umami-related compounds. Cool spring temperatures slow the growth of young shoots, allowing more theanine, free amino acids, and other flavor-enhancing metabolites to accumulate. Chen et al. (2024) used metabolomic analysis of different tea cultivars and found that spring tea contained higher levels of theanine, theogallin, and gallotannins than summer tea. Zaman et al. (2023) analyzed 87 tea cultivars over four consecutive harvest rounds and reported that the first spring flush had the highest average free amino acid content, reaching about 4.0%. Research on Changqing tea also showed that umami-related amino acids declined significantly in summer and autumn teas, while several bitter amino acids increased. These compositional changes give spring tea its characteristic fresh, sweet, smooth taste with relatively low bitterness and astringency. Spring tea also has clear advantages in aroma. White tea and green tea harvested in spring contain relatively high levels of floral and fresh aroma compounds such as geraniol (Zhang et al., 2022). A study of black tea made from the cultivar Baiye No.1 further showed that its sweet and honey-like aroma was closely associated with the accumulation of β-ocimene, geraniol, and citral during the spring season (Chen et al., 2025). Spring tea produced from Rucheng Baimao tea also exhibited stronger floral, fruity, and fresh aromas than summer and autumn teas, resulting in better overall aroma quality (Zhu et al., 2025). However, not every chemical component reaches its highest concentration in spring. Total polyphenols and some catechins can sometimes be higher in summer tea. This indicates that the superior quality of spring tea results from a balanced composition of multiple quality-related compounds rather than from the highest concentration of any single component. Overall, the major strengths of spring tea are its rich umami compounds, pure aroma, and balanced taste. These characteristics make it the preferred raw material for premium green tea, white tea, and high-grade black tea, and it remains the most important source of fresh leaves for famous and high-quality teas. 2.2 Quality characteristics of summer tea Summer tea is generally characterized by stronger bitterness and astringency and lower freshness than spring tea. However, this does not mean that summer tea is of poor quality. Instead, it has its own chemical characteristics and processing advantages. Higher temperatures and stronger sunlight during summer accelerate shoot growth and promote the accumulation of tea polyphenols, catechins, and flavonoids, while reducing the levels of umami-related compounds. As a result, summer tea has a stronger taste but also more pronounced bitterness and astringency. Liu et al. (2023) analyzed a large number of commercial samples of Yinghong 9 black tea and found that total polyphenol content reached 10.24% in summer tea, compared with 9.22% in spring tea. Total catechin content also increased from 30.01 mg/g in spring to 38.28 mg/g in summer. Among these compounds, EC and ECG,
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