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.
Peuyeum (cassava tapai) as part of es doger sweet iced concoction dessert.
Tapai and its variants are usually consumed as it is; as a sweet mildly-alcoholic snacks, to accompany tea in the afternoon. The sweet fermented tapai however, are often used as the ingredient in a recipe of certain dishes. Sundanese cassava peuyeum is the main ingredient for colenak; a roasted fermented cassava tapai served with kinca a sweet syrup made of grated coconut and liquid palm sugar. Colenak is Sundaneseportmanteau of dicocol enak which translates to "tasty dip". Tapai uli is a roasted block of bland-tasted ketan or pulut (glutinous rice) served with sweet tapai ketan or tapai pulut. The peuyeum goreng or tapai goreng, or known in Javanese as rondho royal is another example of Indonesian gorengan (assorted fritters), which is deep friedbattered cassava tapai.
In beverages, tapai, both cassava or glutinous rice, might be added into sweet iced concoction desserts, such as es campur and es doger.