In a large skillet, cook bacon over medium-high, stirring occasionally, until fat is rendered and bacon is slightly browned, about 20 minutes. 

With a slotted spoon, transfer bacon to paper towels to drain. 

Pour off all but 1 tablespoon fat from skillet (reserve for another use); add onions and garlic, and cook until onions are translucent, about 6 minutes. 

Add vinegar, brown sugar, maple syrup and coffee and bring to a boil, stirring and scraping up brown bits from skillet with a wooden spoon, about 2 minutes.  Add bacon and stir to combine.

Transfer mixture to a 6-quart slow cooker and cook on high, uncovered, until liquid is syrupy, 3 1/2 to 4 hours. 

Transfer to a food processor, pulse until coarsely chopped.  Let cool, then refrigerate in airtight containers, up to 4 weeks.