Heat 2 tbsp mirin in a saucepan and allow to bubble for 30 seconds to 1 minute to burn off the alcohol.
Pour the mirin into a container along with 100 ml citrus juice of your choice, 1 ½ tbsp rice vinegar and 125 ml Japanese soy sauce (koikuchi shoyu). Mix well, then add 5 g bonito flakes (katsuobushi) and 10 g dried kelp (kombu) to the container and seal.
Rest in the fridge for at least 24 hours. (Preferably 2-3 days)
Strain the ponzu and transfer to a sterilised container.
Store in the fridge and enjoy!
Notes
For larger batches, store the ponzu in smaller containers and use one at a time to extend the shelf life.Store in the fridge sealed for up to 3 months. Once opened, check for any change in smell, colour and taste and use within 1-2 weeks.