There are no apples in a barrel of grapes. The riddle is designed to be a play on words and misdirection. It presents a scenario that seems unrelated and leads the listener to expect a numerical answer. However, the answer is simply that there are no apples in a barrel of grapes because they are different fruits.
seems there are different types of riddles, to solve the riddle, must one take control of the narrative within the riddle and override it with a corrective narrative which changes the riddle into a new riddle that can be solved or simply explained. riddles are surely fun.