Warm vinegar, sugar and water over a medium heat in a pan, until sugar dissolves. Once the pickling liquor reaches a simmer then remove from the heat.
Add in the miso and stir until dissolved, then add the Peppery Umami salt.
Place the fennel, radish, capers and samphire into a sterilised Kilner jar and pour in the pickling liquor. Leave for 2-3 hours to cool with the lid closed but not sealed. When cool, close the jar fully to seal. Consume within 2-3 weeks.