Place ribs in the slow cooker.
Stir coffee and barbecue sauce together and pour over ribs.
Cook on high 5-6 hours or low 7-8 hours.
Remove ribs from crock.
Stir several tablespoons of bbq sauce from the crock into the cornstarch until smooth.
Pour cornstarch mixture into the rest of the sauce and stir to combine and thicken.
Serve sauce with ribs.