When you first mix the ingredients together, the brine is very salty but it mellows after about half an hour. Don’t make these more than two hours in advance or they will lose their crispness.
Put the vinegar, salt and sugar in a small saucepan over a medium heat and stir until the sugar dissolves. Remove the pan from the heat and leave to cool completely.
Transfer the brine to a non-metallic serving bowl and stir in the bean sprouts and chilli, making sure the bean sprouts are coated in the brine.
Cover and chill for at least 30 minutes before serving, but no longer