Odors in cars tend to linger because of the car's small, enclosed space. Unfortunately, airing a car out does not necessarily get rid of the smells trapped inside. A lot depends on what causes the smell. Beer has a chemical element to it in the alcohol, but organic elements exist as well. Depending on how long a beer spill gets left in a car, mold or mildew can start to grow and compound the odor, even after the spill dries.
Remove the beer stain. If the stain is still wet, soak up as much as you can with a towel and then scrub with water or soda water to dilute and soak up. If the beer has dried, wet it with water or soda water and scrub from the outer edges to the middle. Shampoo the area to get a set-in stain out. Let the upholstery dry for 24 hours.
Sprinkle baking soda on the beer-stained area and rub it into the upholstery with your hands. Baking soda is an absorbent odor remover that can be effective on organic odors. Let it sit for a week.
Vacuum the baking soda out of the carpet. If the beer odor still lingers in the car, move on to Step 4.
Run an ozone generator inside your closed car according to the manufacturer's instructions. The ozone molecules break down organic molecules into gases that do not have a smell. Open the car doors for at least 15 minutes after using the ozone generator to allow the excess ozone to disperse, because it can irritate the lungs. Ozone can also corrode rubber and damage fabrics, so it should only be used sparingly and as a last resort for bad beer smells.