Ripening can then be conducted under controlled conditions of temperature, relative humidity and ethylene to achieve uniform appearance and quality of ripe fruit. Fruit is placed into specially constructed ripening rooms and brought to optimum ripening temperature and humidity. Ethylene is then raised to a prescribed concentration using either a "catalytic generator" that makes ethylene gas from liquid ethanol or from commercially available gas supplies. Forced-air cooling systems ensure that fruit are uniformly exposed to the room ethylene concentration. When fruit are exposed to ethylene under these controlled conditions they will initiate their respiratory climacteric pattern and ripen at a relatively uniform rate. Conditions and duration can be varied to suit customer specifications for stage of ripening and colour development.