Preheat the smoker to 250°F.
In a spray bottle, combine the apple cider vinegar and water. Set aside.
Prep the smoker accordingly. If using a pellet smoker, ensure the hopper is full of pellets. If using a charcoal or propane gas smoker, ensure the water pan and wood whips/chunks are in place.
While the smoker is preheating, put all the dry rub ingredients in a medium size bowl and mix until well combined. Set aside.
Using a sharp paring knife, remove the white membrane from the top of each short rib. To do this, insert the tip of the knife under the membrane and the meat and slightly lift until it becomes separated. Pull away the membrane, cutting where necessary. Expert Tip: Tilt the knife up just slightly to ensure you don't remove any of the raw meat. Add the dry rub onto each side of each beef short rib, pressing lightly so the rub can saturate the top layer of the meat. Set aside.
When the smoker is preheated, place each short rib directly on the grill grates bone side down.
Insert a digital meat thermometer into the middle of the thickest part of a beef short rib. Close the lid and allow to smoke.
After 3 hours into the smoke, spray each rib with the apple cider vinegar and water mixture. Repeat this every hour until done.
The beef short ribs are done when the digital meat thermometer reaches at least 205°F. The probe of the thermometer should insert like you are putting it into room temperature butter. If the ribs are not that tender, continue to smoke until they reach 210°F.
If desired, apply a layer of BBQ sauce to each rib.
Remove each beef short rib from the smoker and allow to rest for 5-7 minutes. Serve.