Combine the base. In a small saucepan, mix apple cider vinegar, ketchup, and water.
Add seasonings. Stir in brown sugar, Worcestershire sauce, paprika, garlic powder, onion powder, black pepper, and optional red pepper flakes.
Simmer gently. Heat over medium-low heat for 5–7 minutes, stirring occasionally until sugar dissolves and sauce is well combined.
Cool slightly. Remove from heat and let the sauce cool for a few minutes before using.
Mop the meat. Use a basting brush to generously mop the sauce over loin while it cooks, repeating every 20–30 minutes for maximum flavor and juiciness.
Serve & enjoy. Reserve some sauce for dipping or drizzling over the finished meat—because who doesn’t love extra sauce?
