Dashi (出汁), plays the same role in Japanese Washoku (和食) cuisine in the same way that stocks are the fundamental building blocks on which French Cuisine is built on. Just like a white canvas to a painter, dashi stock provides the cook with a base on which flavours are built on. This means that the quality of the base dashi stock would have a large impact on the quality of the final product.
Dashi is made by extracting the flavours from Japanese dried kelp, known as Kombu (昆布) as well as Katsuobushi (鰹節) which consists of fermented and smoked skipjack tuna. Bonito, which similar to skipjack tuna are part of the Scombridae family, is sometimes used as a substitute due to its cheaper price. The flavour of dashi is mild and yet very savoury with quite a rich mouthfeel. This is due to the high inosinic acid content found in Katsuobushi and the high glutamic acid content found in kombu. Similar to MSG (Monosodium glutamate), it is the presence of these compounds which give dashi stock its distinctive umami-rich taste. The taste of umami is due to receptors in tastebuds responding to glutamic acid, inosinic acid and guanylic acid.
Katsuobushi is mainly produced at Yaizu in Shizouka, where the freshly caught fish is cleaned and filleted before being simmered. The fillets are then deboned after being cooked at the flesh will have firmed up. They are then smoked for 4-6 hours everyday for up to a month typically using oak wood. In between smoking, the fillets cool down, which allow the moisture trapped inside to rise to the surface, only the be evaporated away the next day. At the very end of the process, the dried fillets are inoculated with Aspergillus glaucus and left to ferment before being sun dried. This process is repeated multiple time until the fillets are as hard as wood. Aspergillus glaucus is in the same family as Aspergillus oryzae (koji) which is used when making sake with the main difference being that Aspergillus glaucus more readily breaks down amino acids and thus ferments protein much better than Aspergillus oryzae which is more apt at breaking down starches. Before the fermentation stage, the fillets can be shaved, packaged and sold as katsuo-kezuri-bushi (鰹削り節) but do not have the same depth of flavour as the fully fermented Katsuobushi. The Aspergillus glaucus culture used is also deemed as a control substance by the Japanese government and thus is not widely available to the public. At this stage, the katsuboshi is ready to be shaved into flakes, with its heading facing towards you and tail facing away when pressing it against the shaver.
Kombu (昆布) on the other hand, is much simpler in preparation, with the freshly harvested kelp just being sun dried. The quality of the Kombu however, is determined based on the temperature ad mineral composition of the waters on which is the Kombu grow in. For example, the town of Erimo (えりも町) is famous for its production of high quality Kombu due it its position being at one of the southern most tip of Hokkaido. This means that the Chishima current mixes with the Tsugara and Tsushima currents blending together the cold and warm water to create optimal conditions for Kombu growth. Kombu harvested in its second year of growth is also considered to have a more superior flavour.
Two types of dashi are made traditionally, Ichiban dashi and Niban dashi. Ichiban dashi, or first broth, is made for the purpose of drinking immediately, while Niban dashi, or second broth, is made from the remnant ingredients used to make Ichiban dashi is used for cooking. Here however, I provide 3 ways to optimise flavour extraction from your ingredients with disregard to these classifications. The resulting dashi is strong enough to be used in cooking and can also be drunk warm.
Japanese Dashi Stock
- 1000g water
- 50g Kombu
- 20g Katsuobushi flakes
- Wipe the Kombu with a damp cloth without removing the white powder on the Kombu.
- Cut the Kombu into multiple smaller pieces to aid in flavour extraction. (Around 5cm by 5cm pieces).
- Use fresh Katsuobushi that has not been exposed to air for long periods of time if possible.
- Add the Kombu to a pan and bring to a simmer, do not boil.
- Once simmering, remove the Kombu and add the Katsuobushi flakes to steep in the hot water for 5 minutes.
- The dashi is ready to use after straining.
- Add the Kombu and Katsuobushi into the water and leave in the fridge overnight (12 to 24 hours)
- The dashi is ready to use after straining.
- Add the Kombu to the water and sous vide at 60-65c for 1 hour.
- Add the Katsuobushi flakes and the water from the previous sous vide bag to a new sous vide bag and bring up to 85c. (If using a ziplock, just replace to Kombu with the Katsuobushi flakes.
- Once at 85c, the dashi is ready to use after straining.
- To make vegetarian dashi, simply remove the katsuobushi from the recipe and add an additional 50% more Kombu.
- The recipe can be scaled to amount needed.
- Thick cut Katsuobushi provides better flavour.
- Katsuobushi should be stored in an airtight container to preserve its quality.
- Do not wash Kombu under running water which will wash away its flavour.
- Do not boil Kombu or you will start to extract bitter and slimy notes from the Kombu.
- The white powder on the Kombu is known as Mannit and should not be wiped off as it consists of nutrients derived from the Kombu that were extracted when drying the kelp. It therefore contributes to the flavour of the dashi.
- If shaving Katsuobushi from an entire fillet, shave with the head facing away from you.
To end with a heartwarming story, 50 years ago during the late 19th century, The town of Erimo underwent severe deforestation which also included the stumps of the trees being uprooted. This ultimately ned to the top soil of the forest being blown into the sea due to its windy location being located so far south on Hokkaido. This led to the roots of the Kombu rotting, which completely wiped out Kombu production. In an effort to restore production. The fishermen came together and planted grass in an attempt to prevent further soil erosion. This effort however was futile due to the strong winds preventing any grass growth of any sort. The solution to the problem came 3 years later when an idea was put forth to cover the ground with seaweed and Kombu rag that had washed ashore from the dead Kombu which not only provided nutrients to the grass but also allowed the grass to stick to the grown and take root. This project was then followed by the planting of black pine trees. In the 1970, 17 years after the start of the reforestation project, it was possible to harvest high quality Kombu from Erimo again.
A legend that existed in Erimo stated that very rarely in the coldest winters, a great amount of ice will flow past Erimo, scrapping the ground and removing any debris and soil that would inhibited the growth of Kombu, allowing for an outstanding harvest of high quality black Kombu. This was documented to have happened in 1984.