The oil yield depends on the quality, the variety and the state of drying of the raw material.
With walnuts, the yield is around 20 %. This means that 100 g of walnuts yield around 20 g of oil.
Pre-treatment is particularly important for walnuts, as the coarse shape of the nut makes it difficult to slide inside the press. The walnuts must be chopped well beforehand and should be dried again in the oven at 80 °C for at least 2 hours. Only then put them in the press.