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Figure 1. 

The overview of historical routes, manufacturing, and morphological types of dark tea. (a) Dark tea trade routes: overland (orange) transported to Asia and Europe; maritime (blue) transported to Southeast Asia, Europe, and the Americas. (b) Traditional and modern processes of dark tea production. (c) Morphological types of dark tea: loose-leaf and compressed.

Figure 2. 

Chemical structural formulas of catechins and their polymers.

Figure 3. 

Chemical structural formulas of flavonoids and flavonoid glycosides.

Figure 4. 

Chemical structural formulas of phenolic acids.

Figure 5. 

Chemical structural formulas of alkaloids.

Figure 6. 

Chemical structural formulas of terpenoids.

Figure 7. 

Chemical structural formulas of amino acids, organic acids, tea polysaccharides, and other compounds.

Figure 8. 

Fermentation environmental factors and microbial regulation in dark tea. (a) Environmental factors in dark tea fermentation. (b) Microbial regulation in dark tea: pure culture, mixed fermentation, and fortified fermentation.

Figure 9. 

Effects of fermentation time.