Layer the ginger and salt in a bowl, cover with a plate, weight down and leave to stand overnight.
Tip the ginger into a colander and drain off as much liquid as possible. Rinse with cold water, drain and dry with kitchen towel.
Add the vinegar, sugar, chilli slices and peppercorns to a saucepan, heat gently until the sugar has dissolved, then bring to the boil and cook over a medium heat for 2–3 minutes. Add the ginger and cook for 1 minute.
Pack the ginger and hot syrup into warm, dry jars, pressing the ginger below the vinegar mixture so that it is completely covered and the jar filled to the very top. Cover with screw-top lids. Label and leave to mature in a cool, dark place for 3–4 weeks.
To serve, use as an accompaniment for sushi.