Zǐjǐn Fàntuán (紫金饭团) is the purple rice roll, a hand-packed sticky rice cylinder built on black or purple glutinous rice instead of white, wrapped tight around a savory core with the rice itself acting as the bread. The angle is compression and contrast carried by a darker, nuttier grain. The rice is both the structure and the wrapper, so the craft is packing it dense enough to hold a generous filling without falling apart while keeping a clear interplay between the chewy, faintly sweet purple grain and a crisp, salty, or rich center. Get it right and you bite through a yielding, deep-colored rice shell into a hot tangle of crunchy fried dough, pickle, and floss; get it wrong and you get a loose handful of bland dark rice with the filling spilling out one end.
The build is a wrap-and-roll assembly with no bread or dough at all. Black or purple glutinous rice, often cut with a little white glutinous rice so it binds well, is steamed until sticky and kept warm so it stays pliable. A sheet of plastic or a cloth is laid out, a bed of the purple rice spread flat, and the fillings laid in a line down the center: classically a length of yóutiáo for crunch, with pickled mustard greens, pork floss, and often a marinated egg or preserved radish. The rice is drawn up and rolled and twisted hard through the wrap so it compacts into a tight log around the core, the fried dough running its length so every bite has crackle. Done well it shows rice pressed firm enough to slice cleanly yet still tender, the purple grain giving a nuttier chew and a darker note than a white roll, a yóutiáo that stays crisp inside the warm rice, and a salty, sour, fatty balance among the fillings. Done poorly the failures show fast: under-packed rice splits and sheds, a stale or omitted fried stick leaves the roll soft and one-note, the purple rice cooked too dry so it will not compress, or an overloaded core that bursts the rice so it will not hold its shape in the hand.
It shifts mostly by the rice blend and the fillings packed inside. A fuller purple or black glutinous mix eats nuttier and chewier than one heavily cut with white rice, and the color carries through to the whole roll. Savory builds lean on floss, pickle, and the fried stick; sweet versions swap in sugar, sesame, or sweet floss for a different register, and the dark rice reads especially well against a sweet treatment. The white-rice roll and the broader family of packed rice cylinders and triangular shapes are their own preparations on the same method and get their own treatment rather than being crowded in here. What fixes this entry is the purple grain specifically, a tightly twisted rice log where dark, nutty glutinous rice is both the wrapper and the body around a crisp, salty core.