Traditionally Katsuobushi is used in blocks and shaved using a wooden grater box. Although Katsuobushi blocks have a much more intense flavor most people nowadays use pre-packages Katsuobushi shavings available in any supermarkets. But once you experienced the intense flavor of real Katsuobushi it will be hard to be content with conventional products.
Raw Bonito fillets are first glutted, sliced and simmered in water for about an hour. Fat, scales and bones are then removed from the soft fillets. The fish slices are then smoked on wood to dry and develop a more complex flavor. Afterwords it is sun dried and exposed to fermentation with four repetitions to further reduce moisture. Katsuobushi only has 20% of the volume of the original fish fillet.