In a cotton gin, water is sprayed into a duct transporting pneumatically conveyed cotton fibers from a gin stand toward a battery condenser to improve the operation of a bale press where the ginned fibers are compacted into a bale. In some embodiments, a taggant is incorporated into the water to mark cotton fibers so threads or fabrics made from the cotton can be identified for quality control purposes. Spray nozzles may deliver water droplets of roughly the same size as the diameter of the cotton fibers. The nozzles may be located on a duct in a location adjacent dead air in the duct to promote coverage of the spray onto the cotton stream. Air may be delivered around the nozzles into the duct to prevent buildup of cotton and debris around the nozzles.