Guide to Inspections of Low Acid Canned Food 30
Manufacturers - 2
to be cooled for repairs or is stopped and cooled for any other reason the retort must be vented when it is brought back up to processing temperature.
Air is removed from the retort during processing by the continuous operation of bleeders which are located within one foot of the outermost product at each end of the retort and not more than 8 feet apart along the top of the retort.
Agitation in this system is intermittent axial agitation. The container rotation can be divided into three phases (Attachment 7) consisting of fixed reel, sliding rotation, and free rotation. The headspace bubble, provided by the gases in the headspace, moves through the product to provide agitation and increased rates of heating in the product during periods of rotation. Maintaining the headspace filed as part of the scheduled process insures a headspace bubble. In the fixed reel portion of rotation the container is carried by the reel through the top 260° of rotation. During this phase no or little agitation of products occurs. As the container approaches the lower 140° of rotation in the retort shell it starts to contact the spiral "T" welded to the interior of the retort shell and begins to turn. This sliding rotation transition phase lasts for approximately 20° of rotation and provides some product agitation. As the container enters the lower 100° of rotation (free rotation phase) the container contacts the retort shell and rotates freely. The majority of agitation occurs in this phase. As the container starts up the side of the retort, sliding rotation takes over and changes to the fixed reel phase. Agitation is dependent upon control of factors such as: headspace, consistency, reel speed and fill weight which must be controlled during processing. Intermittent agitation will increase the heating rate of the product only if the headspace bubble is free to move. Solid pack products will normally not benefit from an agitated process. Some manufactures will still use the continuous retort to process products based on a non-agitating process because of the convenience of the container handling in the continuous system. For products where agitation is not taken into consideration during establishment of the process, headspace may not be critical to the process.
When checking reel speed there are usually two speeds of concern. During process establishment the minimum reel speed is studied. Then scheduled processes are recommended to the manufacturer. When the manufacturing firm sets the retort to meet the scheduled process the reel speed may need to be different to meet the process. For example the RPM for meeting a time of 15 minutes may be 4.2 RPM whereas the minimum RPM is 3.5. The actual RPM should never be less than the minimum RPM and the actual RPM should assure that the scheduled process time is achieved.
Following thermal processing in the processing shell the containers are transferred through a pressure transfer valve to either a pressure cooler or an atmospheric cooler depending upon process temperature and can size. Some containers can be cooled in a Micro-cool valve, where water is sprayed on the containers, to a low enough temperature to allow for atmospheric cooling. The pressure cooler and or Micro-cool valve must be operated at a pressure at least 2 lbs below that in the processing shell to prevent air and water from being forced out of the cooling shell or valve into the thermal processing vessel. The closed cooling shell is approximately 2/3 full of water to provide flood cooling of the containers. Some systems also use an atmospheric open or half-shell cooler where water is sprayed over the containers. The cooling water normally enters the can exit end of the cooling shell and flows to an overflow on the can entry end of the cooling shell. This provides for counterflow cooling of the containers. Additional cold water is added to control the water temperature and to maintain the water level in the cooling shell. The temperature of the cooling water at the can entry end of the cooler is normally at a very high temperature (» 200° F) as the hot cans enter the water. The heating of the cooling water as it passes over the containers tends to drive off chlorine if it is used to sanitize the cooling water. A measurable level of chlorine may not be found in the cooling water at the water discharge point of the cooler shell. If the quality of the water in the cooling shells is not maintained by good sanitary practices such as; sanitation of the cooling water, routine draining and replacement of the cooling water, and cleaning of the cooling shell, excessive microbiological growth in the cooling shells may cause post processing contamination.
If the retort jams or breaks down during processing operations, necessitating retort repairs, the retort must be operated in a manner that ensures commercial sterility of the product. The retort can be operated as a still retort per 21CFR 113.40(c)(8). All containers can be given a still emergency process using a process supplied by the firms processing authority. Any containers in the intake transfer valve and any containers in transfer valves between processing shells have to be removed, given a still process, opened and reprocessed or destroyed. Complete records of the still process must be maintained.
If a temperature drop occurs in the retort the temperature drop should be handled per 21CFR 113.40(c)(9). The retort should be equipped with an automatic device to stop the reel when the temperature drops to below the specified process