Spoiled milk in the close confines of a vehicle is an unpleasant smell and resists many cleaning methods. Use vinegar, baking soda and coffee grounds to eliminate the odor and to keep your car smelling fresh. The process is quick but requires some time for the carpet to dry, which you can reduce by directing a fan on the wet spot.
Soak up the spill
If the milk is still in liquid form, use clean paper towels to soak up as much as possible. Once most of the milk is gone, place several layers of paper towels on the spill, and step with your body weight to remove any remaining traces from the fibers. If there is dried milk on the carpet, use a plastic utensil to scrape it away from the fibers.
Scrub with carpet cleaner
Use spray carpet cleaner to scrub the affected area. The detergents help to release the remaining milk from the fiber.
Wash with vinegar
Apply white vinegar to a rag, and scrub the fibers to remove the odor. If possible, leave the windows down while the vinegar dries.
Apply baking soda
Baking soda is an excellent odor absorber. Sprinkle the spot with baking soda. Apply the solution to the area with a spray bottle, and allow it to stand overnight. Vacuum the powder away.
Spill some coffee
Apply a small amount of coffee grounds over the area of the spill. Leave the coffee overnight, and vacuum the next morning.