Cut the hard base of the broccoli stems. Peel the tough outer layer and then thinly slice the stems into matchsticks, set aside.
In a pot combine water, vinegar, salt and red pepper flakes. Bring to a boil.
Once boiled, turn off the heat and remove from the burner. Add the broccoli stems and let them marinate for 15 to 30 minutes.
Transfer into a storage container and refrigerate until chilled about 3 hours.
Serve and enjoy!