A large airtight container not made of metal or a Ziploc/vacuum-seal plastic bag
A wooden spoon (for mixing)
Wash the korean radish. Peel and cut the radish into half-inch pieces. Exact cubes are not required. If using some other radish in place of Mu, season each of the cut surfaces with black pepper.
In a ziplock bag or airtight plastic container, mix together the vinegar, sugar, and salt. If making a spicy pickle, add the sriracha or chilli flakes now (not both, or the spice will be overwhelming). If all the sugar does not dissolve, don’t worry. The water from the radish will dissolve the rest.
Add the radish to the pickling liquid. Seal the container or bag to prevent oxidation from contact with air. This will greatly affect the taste and texture of the pickle, so be careful!
Open the container to stir the liquid every half hour to encourage moisture loss from the Korean radish. Flip this if you're using a bag. After stirring/flipping 4 times, you are free to leave it unattended overnight in the refrigerator. Serve chilled and enjoy!
Make sure to store this in the fridge overnight for the radish to absorb the flavors. If you have more time, leave this for a further 24 hours. You can adjust the amount of sriracha and chili flakes used to your preference.