Collectors of aged pu-erh and dark teas regularly encounter fungal growth on their cakes. The key distinction is context and species. Eurotium cristatum ('Golden Flower') in Fu brick tea is deliberately cultivated and scientifically validated as safe and beneficial. However, black mould (Aspergillus niger) and green mould (Penicillium) appearing on improperly stored tea indicate excessive moisture and should be treated cautiously. The golden rule: if a mould is white-to-yellow in an adequately ventilated dry storage, it is likely benign. If it is black, green, or accompanied by a foul chemical smell, discard the tea.
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