In a medium saucepan, combine equal parts water and white vinegar along with a pinch of red pepper flakes. Bring to a boil, then remove from heat and let cool for 10 minutes.

Wash and trim celery stalks, cutting them into spears about 4 inches long. Pack the celery tightly in a clean glass jar.

Pour the cooled brine over the celery, ensuring they are submerged. Seal the jar and let it sit at room temperature for 15-20 minutes before refrigerating.

Allow celery to marinate in the fridge for at least 1-2 hours or overnight for the best flavor.