Tro cake is a traditional cake that is a must-have offering to ancestors during the Doan Ngo Festival, a Vietnamese festival known for eliminating pests and diseases that harm crops.
The name “tro cake” comes from its main ingredient, which is glutinous rice soaked in ash water. To ensure the distinct flavor and appearance of the cake, the cook uses ash water extracted from clean straw or medicinal herbs, adding a little lime to create a transparent liquid. The glutinous rice is washed, soaked in ash water for three to four hours, and then drained.
The cake is wrapped in bamboo leaves, dong leaves, or banana leaves. The leaves are scalded in boiling water to ensure cleanliness and prevent the green color from transferring to the cake. The wrapping process requires carefulness and attention to detail to ensure the cake is wrapped tightly and neatly. The cakes are then boiled for four to five hours until they are fully cooked.
Tro cake has an iridescent yellow crust, reminiscent of the golden hue of ripe rice fields. This natural color is achieved from the absorption of ash water into the glutinous rice without the addition of any artificial colors. The filling of the cake typically consists of green or red beans, or sometimes it may be unfilled. Tro cake can be enjoyed with sugar, honey, or sugarcane molasses mixed with a hint of minced ginger.