Fig. 1

Plucking time (A), the first analysis by ¹H NMR spectroscopy (B) of fresh tea leaves between 2015 and 2019, and the reanalysis of all tea leaves after storage at – 80 °C (C). Climate conditions of the tea growing areas in the Seogwang area of Jeju-do, South Korea (D – F). Monthly average temperature (°C, D), total rainfall (mm, E) and total sun exposure time (h, F) recorded from December to April in 2014–2019. All daily climatological data were recorded by an automatic weather station at the tea farm. J2, Jangwon 2 tea cultivar; J3, Jangwon 3 tea cultivar