Because noodles made out of pure buckwheat can easily fall apart when boiled, the buckwheat flour is usually mixed with binders - often wheat flour. Under the Japan Agricultural Standards regulations, the noodles must contain at least 30% buckwheat in order to be called "soba" but noodles with a high buckwheat content are seen as more desirable. The raw noodles are made by making a dough out of buckwheat flour and binder. The dough is then spread out flat. After that, strands of noodles are sliced off with a special knife. The quality of noodles is highly dependent on the skill of the maker, especially for soba noodles with high buckwheat content. The raw noodles are boiled before being served hot or cold.