Remove 1/4 cup bourbon from bottle. Pour warm bacon grease into bottle. Cover and let stand 4 hours, shaking bottle occasionally. Chill 3 to 7 days. Pour bourbon through a wire-mesh strainer lined with a coffee filter into a bowl; discard filter. Clean bottle. Pour strained bourbon into bottle, and store at room temperature up to 6 months.
Note: We tested with Benton's Smoked Country Bacon and Woodford Reserve Bourbon.