BOD (biochemical oxygen demand) bottles are used for the BOD5 or five-day BOD test process that determines the amount of organic compounds present by incubating samples at less than 20°C (68°F). Bottles for BOD are designed so that a solution filling the bottle will push all air out from the bottle. Typically, bottles for BOD feature a permanent white writing area on the side of the bottle to aid in sample identification. Bottles for BOD generally include a flared mouth and glass stopper, which serves to form a tight seal that protects the bottles' contents from outside contamination.