Ponzu

Pour the sake into a pan, bring to the boil over a high heat and flame off the alcohol. When the flames have died down, remove the pan from the heat and set aside to cool.

Wash the yuzu and sudachi, cut them in half and juice them, straining out any seeds. Discard any remaining flesh from the skin and cut them into quarters.

Place the quarters in a large container along with the juice and the rest of the ingredients, apart from the katsuo bushi.

Remove 250ml and add some of the lemon and grapefruit zest and konbu and seal in a small airtight container. This will be your vegetarian ponzu.

Now add the katsuo bushi to the remaining ingredients and refrigerate both containers for one month.

Strain the liquid through damp muslin and adjust the seasoning with tamari, thin mouth soy sauce or vinegar as necessary.

Store in the fridge.