Abstract
Fresh tea leaves change physically and chemically into green tea during the manufacturing process.
1. Tea leaves did not indicate any delayed light emission (DLE) in the processing stages, from the end of tea steaming to final rolling. DLE of tea leaves appeared in the drying stage, increased with time of drying and maintained an almost steady level at the latter stage of drying (Fig. 2).
2. DLE was detected for the first time when the moisture content of tea leaves decreased to about 10 percent (w. b.) in the drying stage (Fig. 3).
3. The DLE spectrum of crude green tea when excited with xenon flash had a primary peak at the wavelength of 565nm (Fig. 5). The DLE was found not to have been emitted from chlorophyll a, but the constituents which emitted the delayed light are yet to be identified.
The fundamental characteristics of DLE for crude green tea were measured as follows.
4. The DLE of crude green tea did not show the “dark recovery”. DLE intensity of crude green tea showed a bit of high value under the shorter dark period and was not affected by dark periods longer than 1 minute (Fig. 4).
5. The DLE of crude tea differed from that of fresh tea leaves and increased proportional to the increase in exciting light intensity (Fig. 6).
6. DLE intensity of crude tea decreased inversely with increase in tea temperature from 12.5 to 45.4°C, and became feeble beyond 40°C (Fig. 7).
7. Fundamental characteristics of DLE of green tea showed similar patterns for Gyokuro, Sencha, and Bancha which were superior, medium, and coarse in quality respectively.
DLE as a means of quality evaluation of crude tea.
8. The DLE intensity of the crude teas wass high in the following order, Gyokuro, Sencha, Bancha respectively (Fig. 8).
9. The quality of Gyokuro and Bancha as pre-determined by their wholesale prices, had a significant correlation with the DLE intensity (Table 2 and 4).
