Nagasaki, introduced through Portuguese-Dutch Dejima port trade in the 16th–17th century; mullet roe drying technology parallels Mediterranean bottarga tradition; modern production centred in Nagasaki city and Isahaya; limited production also in Kochi and Hyogo; autumn harvest from Ariake Sea and Nagasaki Bay mullet
Karasumi (唐墨) is Japan's most prestigious dried roe product — salted and air-dried mullet roe (bora, Mugil cephalus) that is the Japanese equivalent of Mediterranean bottarga. The name 'karasumi' refers to Chinese ink stick (唐墨), whose compressed rectangular shape and dark colour the product resembles. Production: fresh mullet roe sacs are carefully removed without puncturing the membrane, washed in brine, salted for 24–48 hours, rinsed, and then hung or laid flat to air-dry for 2–8 weeks depending on size and climate. The result is a firm, dense, amber-gold block with a surface of fine white salt crystals and an interior that slices to a cross-section showing the amber-red roe. The flavour is intensely savoury, pleasantly briny, with a deep oceanic richness and a sweetness from the roe's natural lipids. Nagasaki is the primary production centre — the city's Portuguese trade connection brought bottarga knowledge (and the mullet) through Dejima, and the Nagasaki karasumi tradition now spans 400 years. The premium season is autumn (October–November) when mullet roe are at their largest and most developed before spawning; prices for top Nagasaki karasumi range from 5,000–20,000 yen per pair (a pair being the two joined roe sacs). Karasumi is served thinly sliced (2–3mm) with sake, grated daikon, or thin slices of rice cake (mochi) — typically as a sake accompaniment or elegant snack rather than a cooking ingredient. Unlike Italian bottarga, which is also used grated over pasta, Japanese karasumi is primarily eaten in thin slices for the direct flavour experience.
Intensely savoury, rich with concentrated roe lipids, pleasantly briny without harshness, with an amber sweetness from the roe's natural sugars; the thin slice delivers maximum flavour surface area; the sensation lingers — umami, salt, and fat in equal measure, each amplifying the other
{"Portuguese-Nagasaki trade connection is the historical source — bottarga knowledge arrived through Dejima port in the 16th century","Autumn production (October–November) at pre-spawn peak produces the most developed, richest roe","Sliced raw (2–3mm) for direct eating — the flavour is the experience, not a background ingredient","Membrane integrity throughout production determines quality — a punctured membrane produces uneven drying and flavour loss","Surface white salt crystals are a quality marker — they form naturally through dehydration and should not be wiped away"}
{"Standard service: thin slices of karasumi, grated fresh daikon, and thinly sliced negi (or a thin mochi disk) — the daikon provides cool pungency that cuts the richness","Karasumi pasta (inspired by Italian tradition): grate karasumi over warm pasta with butter and lemon — a cross-cultural application that works because the roe's salt and umami parallel bottarga","Storage: wrap loosely in parchment and store in the refrigerator at 2–4°C — well-dried karasumi keeps for 3–6 months; it continues to dry slowly and flavour intensifies","Home-drying: if fresh bora roe are available, salt for 36 hours, rinse, hang in a cool airy location for 3–4 weeks — turn daily to ensure even drying; rub daily with sake to prevent surface mold","Nagasaki producers to seek: Hamamoto Karasumi and Nagasaki Karasumi Tairiku are considered benchmark quality; available through depachika and specialty fish shops"}
{"Slicing too thickly — above 4mm, the intense concentrated salt-roe flavour becomes overwhelming rather than nuanced","Storing in a sealed plastic bag — karasumi needs to continue slow drying in the refrigerator; store loosely wrapped in paper or an open container","Removing the surface white salt crystals by washing — these are part of the flavour; if too salty, adjust serving portion rather than washing","Substituting Italian bottarga directly — the flavour profiles differ significantly; Italian bottarga is drier and more aggressively salty, Japanese karasumi is moister and sweeter"}
Nihon Ryori Taizen — Tsuji Shizuo; Japanese Regional Seafood documentation