Tapai is made by inoculating a carbohydrate source with the required microorganisms in a starter culture. This culture has different names in different regions, shown in the table below. The culture can be naturally captured from the wild, by mixing rice flour with ground spices (include garlic, pepper, chili, cinnamon), cane sugar or coconut water, slices of ginger or ginger extract, and water to make a dough. The dough is pressed into round cakes, about 3 cm across and 1 cm thick, and left to incubate on trays with banana leaves under and over them for two to three days. They are then dried and stored, ready for their next use.
Ragi tapai is used to ferment different types of carbohydrates such as cassava, cooked white rice or glutinous rice, and sometimes sweet potatoes. The general process is to wash and cook the target food, cool to about 30°C, mix in some powdered ragi tapai, and rest in covered jars for one to two days. With cassava and sweet potato, the tubers are washed and peeled before cooking, then layered in baskets with ragi tapai sprinkled over each layer.
The finished tapai will taste sweet with a little alcohol, and can be consumed, or left for several days more to become sour.