Bioscience Evidence 2026, Vol.16, No.4, 235-248 http://bioscipublisher.com/index.php/be 238 spring tea, while its bitterness and astringency are weaker than or similar to those of summer tea. Therefore, autumn tea has a relatively balanced quality profile. Research on white tea showed that autumn tea generally contained higher levels of caffeine, total polyphenols, and catechins than spring tea, with ECG showing the greatest increase. This increase was closely associated with the stronger astringency of autumn tea (Huang et al., 2025). Likewise, a study on Lu'an Guapian reported that autumn tea had higher bitterness and astringency but lower umami than spring tea, while its sweetness was intermediate between spring and summer teas (Li et al., 2025a). Although autumn tea loses some of the freshness found in spring tea, its taste is generally less harsh than that of summer tea. Compared with summer tea, autumn tea often has an advantage in aroma. Sensory evaluation of Rucheng Baimao black tea showed that the aroma quality of autumn tea ranked second only to spring tea and was clearly better than that of summer tea, with a cleaner and more balanced aroma profile (Zhu et al., 2025). Pulimamidi et al. (2024) monitored Assam tea throughout the production season and found that EGCG and ECG levels declined from summer to autumn and winter, indicating that some bitter and astringent compounds decreased, although the freshness did not fully recover to spring levels. These seasonal changes produce a relatively balanced combination of aroma and taste in autumn tea. Moderate polyphenol levels, balanced aroma, and relatively stable raw material quality make autumn tea suitable for fermentation and further processing. It can be used to produce dark tea, specialty fermented teas, and other value-added functional products, improving the utilization of autumn-harvested tea leaves. Although autumn tea is less fresh than spring tea, its balanced aroma, stable quality, and good processing potential make it an important component of a year-round tea production system. 3 Main Drivers of Seasonal Variation in Tea Quality 3.1 Effects of temperature on tea quality formation Temperature is one of the most important environmental factors affecting seasonal differences in tea quality. Studies simulating high-altitude conditions have shown that the combination of lower temperature and weaker light suppresses catechin biosynthesis while increasing the accumulation of free amino acids. As a result, the polyphenol-to-amino acid ratio decreases, leading to improved taste and aroma. The optimum temperature for tea plant growth is generally between 20 ℃ and 25 ℃. Higher temperatures regulate the metabolism of catechins, anthocyanins, and theanine through changes in transcription factors, hormones, and structural genes. When the temperature reaches 38°C, the expression of NADH-GOGAT is downregulated, reducing the synthesis of theanine while enhancing the formation of phenylethanol-related volatile compounds (Wu et al., 2025). Short-term low-temperature conditions can increase the accumulation of amino acids, soluble sugars, ascorbic acid, and some flavonoids. They also enhance aroma formation by activating LOX-related genes. Low winter temperatures have likewise been associated with improved tea aroma. The difference between day and night temperatures is another important factor. A diurnal temperature difference of about 10 ℃ is considered favorable for amino acid accumulation, whereas larger temperature differences have inconsistent effects on caffeine, flavonoids, and catechins, suggesting the existence of threshold effects and cultivar-dependent responses. In black tea produced from the large-leaf cultivars Yinghong 9 and Huangyu, tea polyphenols reached their highest level in summer. From spring to summer, soluble sugars and caffeine increased, while free amino acids decreased, and spring-harvested Huangyu tea showed the best overall physicochemical quality (Ye et al., 2022). Temperature effects are also evident within the spring season itself. Yu et al. (2020) reported that Congou black tea made from early spring leaves had better quality than tea produced later in spring. As spring progressed, total polyphenols, total catechins, and EGCG increased, whereas total amino acids declined. Temperature also affects quality during tea processing. Ye et al. (2018) withered fresh green tea leaves at 15, 20, and 25 ℃ for 0~21 h and found that most free amino acids gradually increased during the first 18 h of withering before declining, whereas most catechins decreased as withering time and temperature increased. Based on the
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