The structure of the ground material depends primarily on the screen size, but also on the raw material. For example wheat is easier to grind than barley. Therefore when using the same screen size for both wheat and barley, the result will be a much finer structure on wheat. The water content in the grain also influences on the structure - the more saturated material, the coarser structure. Oats is especially difficult to grind and will often after grinding contain large quantities of whole shell parts which makes it difficult for the feed to flow through the silos.