by Bryan Sekine from SecretsofSushi.com
Su refers to the mixture of rice wine vinegar with salt and sugar.
4 parts vinegar (let’s say 4 cups)
2 parts sugar (2 cups)
1 part salt (1 cup)
To make it, pour the vinegar into a pot and bring it to a medium heat.
Add the salt and sugar and stir until it dissolves.
Let the su return to room temperature naturally.