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Guide to Inspections of Low Acid Canned Food 15

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recording chart be adjusted as closely as possible to the reference MIG thermometer but to be in no event, higher than the known accurate reference thermometer. The working accuracy of most recording devices is at least 1° F (1-1/2ºC). In most instances the recording chart can be adjusted to agree with the MIG thermometer to within 1° F (1-1/2ºC).

The temperature recorder should provide a fine temperature recording line which can be easily read to the nearest 1° F (1/2° C). A conservative approach should always be taken when reading a wide line on a temperature recording curve or line. The temperature recorded should always be determined by reading the bottom of the recorded line on the temperature chart.

The pen arm on a circular chart recorder should follow the time curve on the chart. Failure of the pen arm to follow the time curve indicates that the pen is out of adjustment, bent, or that the wrong chart is being used. It is evident that the pen is not following the temperate curve on the circular chart when it is noted that the temperature curve travels back in time as the pen arm moves up or down on the chart. Some of the more common recorders found in use have a mark inside of the chart case for adjusting the arc of the pen. The number of the chart to use with the recorder may also be stamped inside of the recorder case.

Recorders are driven either by electrical or mechanical wind-up clock mechanisms. If driven by a wind up clock the firm must insure that the clocks are wound on a daily basis. The recorder chart should be adjusted at the beginning of the production day to agree with the time of day. The majority of charts in use can be adjusted to agree at least to within 15 minutes of the time of day. The accuracy of the timing mechanism should be determined over a designated time interval through the use of stop watch. If the timing mechanism is not accurate, the recorder will not provide accurate temperature recordings of the thermal process.

A means of preventing unauthorized changes to the temperature recorder must be provided by the firm. This can consist of a locked recorder box, and/or a posted notice from management that only authorized persons are allowed to make changes.

The temperature recorder probe must be installed in the retort in a manner which will provide a true recording of the retort temperature. The recorder sensing probe is normally installed next to or in the same manner as the MIG thermometer. The recorder is then adjusted to the MIG thermometer.


The lacf regulations recommend that each retort system be equipped with a pressure gauge that is graduated in divisions of 2 lbs or less. A pressure gauge is necessary for observing the pressure during pressure cooling, and processing over-pressure in those systems using air or steam to create pressures higher than those created by the system temperature. The pressure gauge is also an extra safety device which lets the operator know if excess retort pressure is being created.


Vents are large pipes, located opposite the steam entry on steam retorts, used to expel the air from the retort prior to beginning the thermal process. Retort systems other than steam retorts sometimes identify a purge valve, used for removing air from the system to allow for the addition of water to a processing drum or for the rapid introduction of steam to a steam-air retort, as a vent valve. The valves on these systems do not serve the same function as the vent valve on a steam retort. The operation of the vent or purge valve may be critical to the thermal process achieved in the retort system.


Bleeders are small openings required on steam retorts to remove air from the retort during processing, promote circulation, and remove condensate from specific retort systems. A bleeder is also necessary to ensure adequate steam flow past thermometer bulbs. They should be open at all times during venting, come-up and thermal processing. Bleeders must be installed in a manner that allows the operator to observe that they are functioning during operation of the retort.


Mufflers are mechanical devices placed on bleeders or vents of steam retorts to reduce the noise of the escaping steam. If mufflers are used the lacf manufacturing firm must have information on hand in the form of temperature distribution data or other documentation, such as a letter from the manufacturer, that shows that the mufflers do not impede the flow of steam.


Automatic steam controllers are required by the lacf regulations 21 CFR Part 113.40 for all retort systems. The automatic steam controller may operate independently of or in conjunction with the temperature recorder. Steam controllers are of two main types: on/off or modulating. With an on/off system the steam valve is either fully open or fully closed. In a system with an on/off steam valve you would expect to find fluctuations in the temperature

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