Konbu dashi — the clear, faintly oceanic broth extracted from kombu (dried giant kelp, Saccharina japonica) in cold or warm water — is the foundational stock of Japanese vegetarian cooking and the first extraction in the standard ichiban dashi before katsuobushi is added. Konbu's glutamic acid (the amino acid that lends its name to glutamate — umami) leaches into the water passively during cold or warm infusion. The cold extraction (mizudashi) produces a cleaner, more delicate flavour than hot extraction.
- **Cold extraction (mizudashi):** Konbu in cold water, 8–12 hours or overnight in the refrigerator. The resulting dashi is the cleanest, most delicate expression of konbu's glutamate. - **Warm extraction:** Konbu in room-temperature water, brought slowly to 60°C — held at 60°C for 30 minutes, then the konbu removed. 60°C is the optimal temperature for glutamate extraction; above 70°C the konbu's surface alginate dissolves and the dashi becomes slightly slimy. - **The 60°C rule:** At 60°C, the glutamate extraction rate is maximised; the viscous alginate compounds remain bound within the konbu cells. Above 70°C: the cells rupture, releasing alginate, which changes the texture of the dashi undesirably. The konbu must NEVER be boiled. - **The white powder:** The white coating on dried konbu is crystallised mannitol (a sugar alcohol) and glutamic acid — it is the concentrated umami. Do not wash it off. Wipe gently with a damp cloth to remove any grit, leaving the white powder intact. - **Applications:** Vegetarian ichiban dashi (without katsuobushi), vegetarian noodle broth base, chawanmushi for vegetarian diets, and as the base for sunomono (vinegared preparations). Decisive moment: The temperature at 60°C — holding steady for 30 minutes. This requires a thermometer and active management of the heat source. A brief spike above 70°C during this phase degrades the dashi's texture. If no thermometer is available, use the cold extraction method — it eliminates the temperature management challenge entirely.
Tsuji