Vertical still retorts are required to have at least one bleeder opposite the steam entry. Horizontal retorts are required to have at least one bleeder opening within one foot of the outermost location of containers at each end of the retort, and at intervals of no less than 8 feet along the top of the retort. As previously noted, each retort system must be equipped with a MIG thermometer, a temperature-recording device and an automatic steam controller. The sensing bulbs for the MIG thermometer and the temperature recording device may be installed within the retort shell or in an external well attached to the retort. Air may be supplied to the still steam retort to provide overpressure during the water cooling of containers in the retort.
Considerable pressure is built up in the container during thermal processing.
Air overpressure is more easily controlled as the steam tends to collapse in the retort headspace. Crateless retort systems are manufactured by Malo Inc., by the FMC Corp. and by others. Crateless systems are normally operated in a series of from 2 to 6 or more retorts depending upon the firms requirements. One operator can normally operate several crateless retorts at one time. Crateless retorts may be up to 8 feet high and 6 feet in diameter.