Guide to Inspections of Low Acid Canned Food 29
Manufacturers - 2
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wheel at the exit end of the retort and into a second transfer valve which transfers the cans to the next processing or cooling shell while maintaining processing pressure if needed. All of the shells are driven by one variable speed motor or drive mechanism through a series of interconnecting gears to insure that the reels are timed to each other. The drive mechanism is required to be locked or protected by a sign that states that only authorized persons are to make adjustments.
Because of the physical limitations of the reel and spiral T these retort systems are normally limited to a narrow range of can sizes. The length of the can going into the retort can not be longer than the maximum distance between the spirals in the T. The diameter of the can is limited by the distance between the steps in the reel. The number of steps (number of cans around the diameter of the reel) is determined by the can size and the diameter of the reel. For the FMC systems these steps are standardized for can sizes (unless the system has been altered or custom built). The number of steps can be used along with other information to calculate process time.
STEPS PER TURN OF REEL FOR STERILMATIC
CONTINUOUS AGITATING RETORTS
|Can Size||Steps per Turn of Reel|
The container capacity is normally stamped on the end of the shaft of the processing shell.
The length of the process is controlled by the capacity of the retort and the speed at which the reel is turned. The capacity is determined by the length of the retort shell and the number of steps in the reel.
By knowing the retort capacity, the number of steps in the reel and other processing information the following formulas can be used to determine reel speed or process time:
Seconds for 10 reel revolutions = (10 rvs) x (60 secs) x reel steps x process time/capacity
Example: (10x60x47x10)/4136 = 68.18 seconds for 10 revolutions
Containers per minute = Capacity/Process Time
Example: 4136/10 = 413.6 seconds
Revolutions = Capacity/(reel steps x cook time)
Example: 4136/(47x10) = 8.8 per minute (RPMs)
Seconds for 10 revs = (10 rvs x 60 secs x reel steps)/(Cans per minute)
or (10 rvs x 60 sec)/RPM
Example: (10x60)/8.8 = 68.18
The actual process time is determined by using a stop watch and timing 10 revolutions of the retort reel. One arm on the retort reel is selected and observed to pass a stationary mark on the retort shell for the required number of revolutions. Reel speeds that are too fast will cause the product to move through the retort at a faster rate shortening the process time. A reel speed that is too slow will increase the process time but may reduce the agitation of the product and reduce the thermal process given to the product. The process is normally designed with the slowest reel speed (minimum agitation) taken into account. Reel speeds should be checked by the operator at least once every 4 hours. A continuous tachometer record of reel speed may be used in lieu of checking the reel speed by a stopwatch. For those systems which use a tachometer it is recommended that the tachometer be checked on a routine basis against a stopwatch for accuracy.
The standard continuous agitating retort systems are designed to operate over a wide range of temperatures up to 275° F (135° C), with custom designs operated at temperatures of up to 294° F
Steam is fed into the bottom of the sterilizer through a steam manifold to a steam trough in the bottom of the retort. The condensate that forms in the bottom of the retort from cold containers continuously entering the retort must be removed to prevent the condensate from building up and touching the containers. This not only cools the containers but may prevent agitation of the product in the containers. Condensate is normally removed during venting by opening the drain valve in the bottom of the retort. After the retort is up to processing temperature continuous draining of the condensate is through a 3/4 inch drain valve left partly open or through an automatic condensate trap. A 1/8 inch (minimum) bleeder is required in the bottom of the steam trough to provide visual assurance to the operator that there is no condensate buildup in the retort.
Venting of the retort takes place at the beginning of the production period and need not be performed again as long as the retort is not cooled. Venting should be performed as per the retort manufacturers or processing authorities instructions. The FMC continuous retort is normally vented for 7 minutes to 220° F through the two 2-inch vents located in the top portion of the retort shell. If the retort shell has
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