Orangutans’ diet are made up of bark, leaves, flowers, a variety of insects, and most importantly, over 300 kinds of fruit, with durian being one of their favourite! Orangutans are even able to eat fruit that are unripe, giving them an advantage over other fruit eaters.

http://www.30bananasaday.com/forum/topics/what-did-orangutans-eat-tens

Mothers teach their babies what food to eat and where to find them and during which seasons to find them. The orangutan has a very detailed map of the forest in her mind and a very detailed knowledge on the fruit cycles of different trees.