Zong zi (粽子) are glutinous rice dumplings wrapped in bamboo leaves (or reed leaves in some regions) and boiled or steamed for several hours — the iconic food of the Dragon Boat Festival (Duan Wu Jie, 端午节, the 5th day of the 5th lunar month). They are made in enormous regional variety: northern Chinese zong zi tend to be sweet (filled with red bean paste or jujubes); Cantonese zong zi (the most elaborate) contain savoury fillings of pork belly, egg yolk, chestnuts, dried mushrooms, and dried shrimp; Hakka zong zi are typically smaller and tied in a specific triangular shape. The wrapping technique — folding bamboo leaves into a cone, filling with rice and fillings, and binding tightly with string — is a significant domestic skill passed down through generations.
The wrapping technique: Soak bamboo leaves overnight. Fold 2-3 leaves into a cone shape by bending the leaf back on itself to create a funnel, with no gaps at the base. Fill the cone with a layer of soaked glutinous rice. Press the filling (pork belly cube, salted egg yolk, mushroom, etc.) into the center. Cover with more rice. Fold the remaining leaf over the top to seal. Bind tightly with kitchen twine in a cross-binding pattern to prevent the cone from opening during cooking. The cooking: Zong zi are cooked in a large pot of boiling water — completely submerged, held below the surface with a heavy plate. Cook at a rolling boil for 2-3 hours (smaller ones) to 3-4 hours (large Cantonese versions). The long cooking time fully hydrates and cooks the glutinous rice and allows the flavours to penetrate throughout.
Eileen Yin-Fei Lo, Mastering the Art of Chinese Cooking (2009); Fuchsia Dunlop, Every Grain of Rice (2012)