Dairy Establishment Inspection Manual – Chapter 13 - Thermal Processing Tasks

This page is part of the Guidance Document Repository (GDR).

Looking for related documents?
Search for related documents in the Guidance Document Repository

Retort (Canning)

1.13.01.01 Empty Product Containers

The manufacturer must have written specifications for containers and ends (physical dimensions, double seam dimensions, material and performance specifications) and a system to verify if specifications are met by each supplier, including the appropriate records.

Empty product containers must be re-inspected by plant quality control personnel before use, for signs of damage incurred during transportation and storage and for compliance with the manufacturer's specifications.

The packaging material should be sound and should provide appropriate protection from contamination. The product containers should be sufficiently durable to withstand the mechanical, chemical and thermal stresses encountered during thermal processing and normal distribution. Inspection is particularly important in the case of glass containers which may contain fragments of glass or glass defects which are difficult to see.

All packaging material should be stored in a clean and sanitary manner. Care should be taken to avoid damage to empty containers, closures and container materials which can result from faulty handling prior to closure.

The manufacturer must implement a regular monitoring program to ensure that unsuitable containers are not used for processing. Some examples of unsuitable containers are explained below.

Empty containers are particularly subject to damage by faulty operation of depalletizers and by badly designed or poorly controlled conveyors to filling and seaming machines.

Immediately prior to filling, rigid containers should be cleaned in an inverted position by suitable air or water jet appliances. Glass containers may also be cleaned by suction (vacuum). Containers intended for use on aseptic filling lines should not be cleaned with water unless they are thoroughly dried prior to sterilization.

Product containers must never be used within the cannery for any purpose other than packing food. They must never be used as ash trays, waste containers, receptacles for small machine parts or any other similar purposes. Such practices must be avoided because there is a considerable risk that such containers may accidentally find their way back onto the production line and result in the packing of food in the same container with very objectionable or possible dangerous material.

Empty containers should be removed from the packing room and from the conveyors which lead to the filling machines before production lines are washed down. If this is not practicable, they must be shielded or located so that they will not become contaminated or obstruct the clean-up operations.

1.13.02 Filling and Sealing Equipment and Operation

1.13.02.01 Equipment Conditions

Under processing, inadequate vacuum or seam defects could result from improper design, construction, installation and maintenance of filling and sealing equipment.

All equipment must be made of a material which is non-absorbent, non-toxic, free from pitting, cracks or crevices, corrosion resistant and is capable of withstanding repeated cleaning and disinfection. The equipment design should ensure that the product does not become contaminated; surfaces should be smooth and easily cleaned and disinfected; the equipment should be visible for inspection.

1.13.02.02 Control Factors

The initial temperature of the contents of the coldest containers to be processed shall be determined and recorded with sufficient frequency to ensure that the temperature of the product is no lower than the minimum initial temperature specified in the scheduled process. In the case of hot fill operations, this would be one of the first containers to go into the retort, in the case of cold fill operations, one of the last to go into the retort. An appropriate sample container is selected, the contents are stirred and the temperature recorded using a thermometer.

Thermal processing shall be commenced as soon as possible after closing to avoid microbial growth or changes in heat transfer characteristics of the products. (As a general rule, the time between sealing the filled container and thermal processing should not exceed 60 minutes). During breakdowns or when production is low, product may have to be processed in partially loaded retorts or pasteurizers in order to comply with the time limitation. In such instances, changes to the thermal processing parameters including venting procedures, where applicable, may be required.

The filling of containers also has a direct bearing on the resulting headspace. Insufficient headspace will not allow for sufficient expansion during the thermal process and in the case of glass containers, this may lead to deformation of the closure. In the case of double seamed containers, excessive pressure may result in distortion of the ends of the container.

Controlled filling, whether by mechanical or manual means, is also important in respect to heat penetration. In agitating retorts, it is the movement of the headspace bubble through the product which ensures the mixing of the contents and even heat distribution throughout the product.

Small deviations from the product and filling specifications which may seem negligible can cause serious deviations in the heat penetration characteristics of the product.

For rotational sterilization, viscosity rather than the consistency can be an important factor and shall not only be specified but also controlled at the specified level.

Controls need to be in place to prevent damage or interference in the sealing area prior to closing as this may interfere with adequate double seam formation.

Measurements of the control factors must be made and recorded at intervals of sufficient frequency to ensure that they are as specified in the scheduled process; intervals should not exceed 15 minutes.

1.13.02.03 Handling of Filled Containers

At all times containers should be handled in a manner that protects the container and its closure from damage which may cause defects and subsequent microbial contamination. Design, operation and maintenance of container handling methods should be appropriate for the types of containers and materials used. Poorly designed or incorrectly operated container conveying and loading systems are known to cause damage.

Care should also be taken with semi-and fully automatic crate loading systems as well as in-feed conveyor systems to continuous sterilizers. The accumulation of stationary containers on moving conveyors should be avoided or kept to a minimum number as this can result in damage to the containers.

Where necessary, filled and sealed containers should be thoroughly washed before sterilization to remove grease, dirt and product from the outside of the container.

Not only is it more difficult to wash containers after sterilization, but it can also increase the risk of post-processing contamination.

1.13.02.04 Coding

The code mark shall identify the establishment in which the product was thermally processed, the product, the year and the day of the year when thermally processed. A key to the code marks employed must be made available to the inspector upon request.

Each container shall be marked with an identifying alphanumeric code which is permanent, legible and does not adversely affect the container integrity. Where the container does not permit the code to be embossed or inked, the label may be legibly perforated or otherwise marked and securely affixed to the product container at the time of packing.

1.13.03 Container closure evaluation

1.13.03.01 Visual Inspection

The closing machine operator, (includes seaming and sealing), closure supervisor or other competent person shall visually examine at least one container from each seaming, sealing, turret feed or closure head after closure has been completed at intervals not to exceed 30 minutes during operation of the closure machines. Each container shall be examined for the presence of externally visible defects, particularly at the seams, seals or closures. All observations shall be recorded.

Visual inspection should be carried out using the hand as well as the eye. Sometimes it is easier to feel a defect rather than see it. By running the fingers around the seam both on the inside and the outside, it is possible to detect any roughness, unevenness or sharpness. A description of visual inspection of the can and the commonly observed defects in metal containers as well as the most probable causes can be found in Chapters 4 to 7 inclusive of The Metal Can Defects Identification and Classification Manual published by the Canadian Food Inspection Agency, and in various manuals published by the can manufacturers, closure machine manufacturers and manufacturers of sealing compounds. Processors are advised to consult these manuals and become familiar with their contents.

Additional visual inspections and non-destructive measurements shall be made and recorded following a jam, an adjustment to or start-up following a prolonged shut-down of a closure operation.

When defects which may affect the integrity of the container or measurements outside of those specified for the closure are observed, immediate corrective action should be taken and recorded. All products from the time of the last inspection should be subjected to an evaluation to ensure that the integrity of the containers has not been compromised. Suspect containers should be set aside for further evaluation.

1.13.03.02 Seam Teardowns

In addition to regular observations for container external defects by visual inspections, tear-down or destructive inspections and evaluations of the closures from at least one container from each seaming, sealing, turret feed or closure head shall be performed and recorded by a competent individual at the start-up of the closure operation and at intervals of sufficient frequency not to exceed 4 hours to ensure that the closure specifications are attained and maintained. Additional destructive examinations of closures shall be made immediately following a jam in a closure machine, after adjustment or after shut-down due to faulty seams or mechanical problems. Generally the closure performed on site is subject to the closest inspection at this stage, however it is advisable to similarly inspect and evaluate any closures made by the container manufacturer of at least one of the containers taken at any inspection period.

In routine tear-down examination of a double seam both methods may be used, in that, a single cross-section is taken and the appropriate measurements made optically with the remainder of the double seam being torn down for further measurements and evaluations.

Other double seam measurements which can be made at the same time are used in the assessment of the seam quality:

  • Countersink depth (A)
  • Double seam thickness (S)

These should be made at the same points used for the double seam length.

In the tear-down inspection of a double seam the following measurements should be made:

  • Overlap
  • Tightness rating
  • Juncture rating for soldered side seam cans

Visual observation of the pressure ridge, where applicable, is useful in evaluation of double seam tightness.

In addition to these, especially when the overlap is to be calculated using one of the formulas, the following measurements should be made:

  • Body hook length (BH)
  • Cover hook length (CH)
  • End plate thickness (Te)
  • Body plate thickness (Tb)

In some instances the body hook and cover hook lengths are useful measurements in control of double seam quality and should be measured at least three separate points about the torn-down seam as described for the double seam length above.

Overlap

The overlap can be determined directly from a suitable cross-section cut of the double seam or by calculation. The following formulas are used to calculate the overlap:

  1. Overlap = 0 = (CH + BH + Te) - W
  2. Percent Overlap = %0 = (BH + CH + Te - W) times 100 divided by (W - (2 Te + Tb))

The appropriate dimensions to be used are indicated by their respective letter symbols in Appendix 9.

The overlap, body hook and cover hook lengths can be measured direct from a magnified cross-section image of a double seam with a seam scope and appropriate calipers or micrometers. The cross-section segments to be examined should be taken at least two or more places equally spaced around the double seam, excluding the juncture with the side seam.

The measurements and evaluations as well as their trends are important in the assessment of the closure integrity for control purposes. The recording of measurements and observations should permit the evaluation of trends, that is to say, quality control charts.

The instructions and specifications of both the container and the sealing machine manufacturers should be accurately and continuously followed in the assessment of the measurements, their trends and evaluations as well as those of the appropriate federal, provincial or municipal agency having jurisdiction.

1.13.04.01 - 1.13.04.04 Indicating Thermometer (Retort)

Each retort shall be equipped with at least one indicating thermometer. It shall be mercury actuated or resistance temperature devices (RTDs). The indicating thermometer, not the recorder chart must be the official instrument for indicating the processing temperature.

Mercury actuated or accepted equivalent thermometers shall be of direct reading type, contained in a corrosion resistant case which permits easy observation of column and scale. The filling above mercury is to be nitrogen or equally suitable gas. The bulb shall be Corning normal or equivalent.

The RTDs type must be fail-safe, accurate, reliable, and meet the scale and thermometric response specifications. The criteria in Appendix 13 - Design Requirements for Digital Thermometers shall be used to evaluate RTDs when used as alternatives to mercury actuated direct reading thermometers.

This thermometer shall have divisions that are easily readable to 0.5°C (1°F) and whose scale does not contain more than 4°C per centimetre (17°F per inch) of graduated scale. Thermometers shall be tested for accuracy against a known accurate standard thermometer. This should be done in steam or water as appropriate and in a similar aspect or position to that in which it is installed in the retort. Such tests shall be performed just prior to installation, and at least once a year thereafter or more frequently as may be necessary to ensure their accuracy. A dated record of such tests must be kept. A thermometer that deviates by more than 0.5°C (1°F) from the standard thermometer reading shall be replaced. A daily inspection of thermometers shall be made to detect and replace thermometers with divided mercury columns or other defects which may impede their accuracy.

The indicating thermometers shall be located so as to be accurately and easily read, since these are the reference instruments for indicating the processing temperature, not the recording thermometers.

Testing methods must comply with the required standards, and must show satisfactory follow-up on out of specification findings. Plant management must investigate the safety of the product produced with out of calibration equipment.

1.13.05.01 - 1.13.05.04 Pressure Gauges

Each pressure vessel or retort shall be equipped with an accurate and reliable pressure gauge. The gauge shall be checked for accuracy at least once a year. All records of accuracy and maintenance must be kept on file. The gauge shall be set so as to read zero at the prevailing atmospheric pressure. The scale shall have a range such that the safe working pressure of the retort is approximately two-thirds of the full scale and be graduated into divisions not greater than 14 KPa (2 psi). The gauge dial shall be large enough to be easily and accurately read (diameter not less than 10 cm). The instrument may be connected to the retort by means of a gauge siphon or gooseneck.

Each retort shall be equipped with a pressure safety valve having a capacity sufficient to prevent undesired increases in the retort pressure. Such valves shall be of a type and installed in a manner approved by the agency having jurisdiction. If a retort is used only at atmospheric pressure, a pressure safety valve may not be necessary.

1.13.06.01 Preheater/Sterilizer

The steam supply must be adequate to meet the minimum requirements for venting and processing under all operating conditions (e.g. the steam supply must be adequate to meet the maximum demand for venting multiple retorts).

The steam inlet to each retort shall be large enough to provide sufficient steam for proper operation of the retort, and shall enter at a suitable point (generally opposite) to facilitate air removal during venting.

Steam spreaders are perforated continuations of the steam line inside the retort and should not be larger than the steam inlet line.

Perforated steam spreaders, if used, shall be checked regularly to ensure they are not blocked or otherwise inoperative. Horizontal still retorts shall be equipped with perforated steam spreaders that extend for the full length of the retort. In vertical still retorts perforated steam spreaders, if used, shall be in the form of a cross or coil. The number of perforations in spreaders for both horizontal and vertical still retorts shall be such that the total cross-sectional area of the perforations is equal to 1.5 to 2 times the cross-sectional area of the smallest part of the steam inlet line.

Each retort, product sterilizer or pasteurizer in which steam is the source of heat shall be equipped with a steam controller to maintain the desired temperature. This may be a recording-controlling instrument when combined with a recording thermometer.

1.13.07.01 Bleeders and Condensate Removal

Bleeders are pet cocks used to remove any air entering the retort with the steam. They also provide circulation of steam in the retort and past thermometer bulbs in wells. Bleeders shall be of a suitable size, e.g. 3 mm (1/8 inch) and location and shall be fully open during the entire thermal process, including the come-up-time. In retorts having top steam inlet and bottom venting, a bleeder or other suitable device shall be installed in the bottom of the retort to continuously remove condensate. All bleeders shall be arranged in such a way that the operator can observe that they are functioning properly. Bleeders are not part of the venting system.

At the time the steam is turned on, the drain shall be opened for a time sufficient to remove steam condensate from the retort and provision should be made for continuous drainage of condensate during the retort operation. The bleeders in the bottom of the shell serve as an indicator of continuous condensate removal. The retort operator shall observe and periodically record how this bleeder is functioning.

Bleeders and vents may be equipped with mufflers or noise suppressors to reduce their noise level. If mufflers are used, evidence that they do not significantly impede air removal must be kept on file. This may be the form of heat distribution data. A letter from the manufacturer, the designer or a competent processing authority may also serve this function. Bleeder and vent mufflers should be periodically checked for proper operation. If clogged or in disrepair, they should be repaired or replaced.

1.13.08.01 Process Timing

An accurate, clearly visible clock or other suitable timing device shall be installed in the thermal processing room and times should be read from this instrument and not from wristwatches, etc. Where two or more clocks or other timing devices are used in a thermal processing room they shall be synchronized.

Processes should not be timed by observing the recording thermometer. Extreme care is required for process timing at higher retort temperatures. Even a process time slightly shorter than recommended will, at higher retort temperatures, drastically lower the lethality of the process.

1.13.09.01 - 1.13.09.03 Venting

To ensure adequate removal of air from the retort and uniform temperature distribution during thermal processing, venting schedules shall be established with correctly applied temperature distribution studies. Such studies shall be carried out by persons competent and experienced in thermal processing. Records of all studies shall be made available to the inspector upon request and maintained.

Vent systems should be as short as possible. They should be designed to eliminate as many bends as possible. Exceptionally long or restricted vent pipes can result in an unusually long come-up period which in turn could result in under-processing:

  1. Vents shall be installed in such a way that air is removed from the retort before timing of the process is started
  2. Vents shall be controlled by gate, plug cock or other adequate type valves and must be fully open to permit rapid discharge of air from the retort during the venting period
  3. Vents shall not be connected directly to a closed drain system. If the overflow line is used as a vent, there shall be an atmospheric break in the line before it connects to a closed drain
  4. Vent should be located in that portion of the retort opposite the steam inlet; for example steam inlet in bottom portion and vent in top portion
  5. Total cross-section area of steam vent outlets shall always be greater than the cross-section area of the steam inlet

When a retort manifold connects several vent pipes from the horizontal single retorts, it shall be controlled by a gate, plug cock or other adequate type of valve. The retort manifold shall be of a size such that the cross-sectional area of the pipe is larger than the total cross-sectional area of all connecting vents.

The discharge shall not be directly connected to a closed drain without an atmospheric break in the line.

The steam valve is to be wide open. Using a steam controller to regulate the supply of steam before the vent temperature requirement has been reached invalidates the concept of venting. This is because the control valve will oscillate between fully open and fully closed (unless the retort controller is proportional). This means that the flow of steam will shut off intermittently during the vent. Manual throttling of the bypass reduces the flow of steam but does not shut it off. If such throttling is required temperature distribution studies shall be undertaken to prove the vent effectiveness.

Bleeders and vents may be equipped with mufflers or noise suppressors to reduce their noise level. If mufflers are used, evidence that they do not significantly impede air removal must be kept on file. This may be the form of heat distribution data. A letter from the manufacturer, the designer or a competent processing authority may also serve this function. Bleeder and vent mufflers should be periodically checked for proper operation. If clogged or in disrepair, they should be repaired or replaced.

1.13.10.01 - 1.13.10.02 Scheduled Process

The thermal process is the application of heat to a raw product in a hermetically sealed container for a period of time at a particular temperature that has been calculated to be adequate for commercial sterility. It is determined using heat penetration test data and heat resistance knowledge by persons having expert knowledge and experience in thermal processing. The results of all tests and calculations used to determine the thermal process, as well as those to establish the critical factors and their verification must be incorporated into the scheduled process.

As a minimum, the scheduled process shall contain the following data:

  • Levels and types of preservatives
  • Product and filling specifications, including any restrictions on ingredient changes or formulation including dimensional tolerances of solid ingredients
  • Container size (dimensions) and type
  • Container orientation and spacing in retort where appropriate
  • Ingoing weight of products including liquid where appropriate
  • Residual air content in the sealed container (flexible and semi-rigid containers)
  • pH of the product, where applicable
  • Minimum initial temperature
  • Water activity of the product, where applicable
  • Venting procedures, where applicable. (these should be determined on fully loaded retorts only)
  • Type and characteristics of the thermal processing system(s)
  • Sterilization temperature
  • Sterilization time
  • Overpressure, where applicable
  • Cooling method, where applicable
  • Date determined and source or processing authority

This process is very specific to one particular food formula prepared in a standardized manner and heat processed in one type of retort system. A process must never be altered unless instructions to do so have been obtained (and documented) from personnel familiar with process determinations.

1.13.11.01 - 1.13.11.05 Temperature/time Recording Device

Each retort, product sterilizer or pasteurizer shall be equipped with at least one temperature/time recording device. This may be combined with a steam controller, such as, a temperature controlling and recording instrument. It is important that the correct chart be used for each device. The chart should have a working scale of not more than 12°C to the centimetre (55°F to the inch) within the range of 10°C (18°F) of the sterilizing or process temperature and the chart graduation should not exceed 1°C (2°F) within 6°C (11°F) of processing temperature. The recorder shall be calibrated so that the temperature indicated is not greater than the temperature of the indicating thermometer. A means of preventing unauthorized changes in the adjustment shall be provided. It is important that the chart be used to provide a permanent record of the thermal processing temperature in relation to time. The timing device shall be accurate, reliable and checked as often as necessary to ensure that its accuracy and reliability is maintained.

Recorder charts shall be identified by date, product, container size, retort and, where applicable, the cooker shell number and other data as necessary, so they can be correlated with the written record of lots processed. Each entry on the record shall be made by the retort or processing system operator, or other designated person, at the time the specific retort or processing system condition or operation occurs, and the retort or processing system operator or such designated person shall sign or initial each record form. Prior to shipment or release for distribution, but not later than one working day after the actual process, a representative of plant management who is knowledgeable and experienced in canning technology shall review and ensure that all processing and production records are complete and that product received the scheduled process. The records, including the recorder thermometer chart, shall be signed or initialed by the person conducting the review.

Testing methods must comply with the required standards, and must show satisfactory follow-up on out of specification findings. Plant management must investigate the safety of the product produced with out of calibration equipment. All records of accuracy and maintenance must be kept on file.

1.13.12.01 - 1.13.12.04 Retort and Reel Speed Timing

The rotational speed of the retort or reel is critical and should be specified in the scheduled process. The speed should be adjusted and recorded when the retort is started, and at intervals of sufficient frequency to insure that the retort speed is maintained as specified in the scheduled process. If a change of speed inadvertently occurs, this should be recorded together with corrective action taken. Additionally, a recording tachometer may be used to provide a continuous record of the speed. The speed should be checked against a stop watch at least once per shift. A means of preventing unauthorized speed changes on retorts should be provided.

1.13.13.01 - 1.13.13.03 Cooling

To avoid thermophilic spoilage and/or organoleptic deterioration of the product, the containers shall be cooled as rapidly as possible to an internal temperature of about 40°C (105°F). (In practice, water cooling is used for this purpose. Further cooling is done in air to evaporate the adhering water film. This aids in preventing both microbiological contamination and corrosion). If indicated, extra pressure can be applied during cooling to compensate for the internal pressure inside the container at the beginning of cooling, to prevent the deformation or leakage of containers. This can be minimized by equating the over pressure with the internal container pressure. When the integrity of the container is not adversely affected, water or air under atmospheric pressure may be used for cooling. (Extra pressure is commonly achieved by introducing water or compressed air into the retort under pressure). The container and closure manufacturers' instructions should be followed.

It is essential that cooling water storage tanks be constructed of impervious materials and protected by close fitting covers thus preventing contamination of the water by seepage, entry of surface water or other sources of contamination. These tanks shall also be fitted with baffles or other means of ensuring thorough mixing of water and chlorine or the disinfectant. They shall be of sufficient capacity to ensure that the minimum residence is achieved.

(Although containers may normally be considered hermetically sealed, a small number of containers may leak during the cooling period mainly due to mechanical stress and pressure differential). Cooling water should consistently be of low microbial content. (e.g. an aerobic mesophilic total colony count of less than 500 colony forming units (CFU)/mL). Records shall be kept of cooling water treatment and of its microbiological quality.

If water to be used for cooling does not meet with this microbiological specification then it must be treated in a manner which will ensure that at the time of use it will meet the specification. While chlorination is generally used as an effective treatment, other treatments such as ozone, iodine compounds, etc. may be used.

The adequacy of a suitable chlorination treatment may be established by:

  1. Presence of a measurable residual free chlorine in the water at the end of the contact time and
  2. Detectable amounts of residual free chlorine in the water after is has been used for cooling containers. (Residual free chlorine content of 0.5 to 2.0 ppm is usually considered adequate. Chlorine levels in excess of this may accelerate corrosion of certain metallic components.)
  3. Low microbial content of the water at the point of use

Once a suitable system has been established, the adequacy of treatment is indicated by measuring and recording the free residual chlorine according to b) above. In addition, water temperature and pH shall be measured and recorded since marked changes from the reference values previously established may adversely affect the disinfecting action of the added chlorine.

(The amount of chlorine required for adequate disinfection will depend upon the chlorine demand of the water, its pH and temperature. Where water with a high level of organic impurity, (e.g. surface water) is used as a source of supply, it will usually be necessary to provide suitable treatment for separation of impurities, prior to disinfection by chlorine thereby reducing excessive chlorine demand. Re-circulated cooling water may gradually increase in organic load and it may be necessary to reduce this by separation or other means. If the pH of cooling water is greater than 7.0 or its temperature is above 30°C it may be necessary to increase the minimum contact time or concentration of chlorine to achieve adequate disinfection. Similar actions may be necessary with water disinfected by means other than addition of chlorine.)

1.13.14.01 Post Process Container Handling

The container must be handled in a manner that ensures that it remains hermetically sealed. A small proportion of correctly made and closed cans may be subject to temporary leaks (microleakage) during the later stages of cooling and for as long as the cans and their seams remain externally wet. The risk of microleakage may be increased if poor seam quality and inadequately designed container conveyor, handling, labelling and packaging equipment result in increased can abuse. When such leakage occurs, water on the can provides a source and a transport medium for microbial contamination from conveyor and equipment surfaces to areas on or near the can seams. To control leaker infection it is necessary to ensure that:

  1. Cans are dried as soon as possible after processing
  2. Conveying systems and equipment are designed to minimize abuse; and
  3. Conveyor and equipment surfaces are effectively cleaned and disinfected

Where used, driers shall be shown not to cause damage to or contaminate containers and shall be readily accessible for routine cleaning and disinfection. Not all driers meet these requirements. The drying unit shall be employed in the line as soon as practicable after cooling.

(Driers do not remove all cooling water residues from container external surfaces but they reduce significantly the time containers are wet. This reduces the length of post-drier conveying equipment that becomes wet during production periods and which requires extra cleaning and disinfection measures.)

Mechanical shock or abuse is mainly caused by either containers knocking into each other, (for example, on gravity runways), or by pressing against each other, (for example, when the backup of containers on cable runways results in the development of excessive pressure). Abuse may also be caused by containers hitting protruding sections on conveying systems. Such mechanical shocks may cause temporary or permanent leaks and result in infection if the containers are wet.

Careful attention to the design, layout, operations and maintenance of conveying systems is necessary if abuse is to be reduced to a minimum. (One of the most common design faults is unnecessary changes in the height of different sections of the conveying system. For line speeds above 300 cpm (containers per minute), multi-lane conveying systems coupled with container accumulation tables are recommended. Sensors should be installed to allow the conveyor to be stopped if excessive build-up of containers occurs.) Poor seam quality in combination with inadequately designed, adjusted or maintained unscrambling, labelling and packaging equipment increases the risk of microleakage.

Any container conveyor or equipment surface that is wet during production periods will permit rapid growth of infecting microorganisms unless it is effectively cleaned at least once every 24 hours and, in addition, regularly disinfected during production periods. The chlorine in the cooling water deposited on these surfaces from cooled cans is not an adequate disinfectant. Any cleaning and disinfection program that is instituted shall be carefully evaluated to ensure that microbial loads are reduced to a minimum before being adopted as a routine procedure. The assessment of the continuing effectiveness of post-process cleaning and disinfection programs can only be established by bacteriological monitoring.

Conveying systems and equipment shall be critically examined with the view to replacing unsuitable materials. Porous materials shall not be used and surfaces which become porous, heavily corroded or damaged shall be repaired or replaced.

Controls are to be in place to prevent mislabelling and the potential to mislead segments of the population which may be allergic to certain foods. Different production runs that may contain different additives, vitamins, need to be effectively separated and labelled appropriately.

All personnel shall be made fully aware of the importance of personal hygiene and good habits in relation to post-process container handling.

1.13.15.01 Incubation Test

The term incubation refers to the holding of sample(s) of hermetically sealed, processed foods at a specified temperature for a specified period of time, before examination for signs of spoilage. The incubation of canned foods serves several purposes:

  1. It provides for a routine survey of daily canning operations to determine if any spoilage exists.
  2. It determines the extent of spoilage that might be due to defective seams or closures.

Since low acid canned foods have the potential to cause botulism, it is imperative that a sampling plan for incubation testing be implemented. However, it is quite possible that, if present, Clostridium botulinum would be expected to occur at such a low frequency that no conceivable sampling plan would prove adequate as a direct measure of its presence. Therefore, emphasis should be placed on process controls (i.e. adequate thermal process based on records, package integrity data) and implementation of an effective plant sanitation program.

A sampling plan must be selected to obtain an accurate cross-section of production. For example, it may necessitate drawing a sample at the start of each day's operation, after major shut downs as well as one sample per hour.

It is suggested that cans be incubated at 37°C (98.6°F) for 10 days. To determine thermophilic spoilage incubation at 55°C (131°F) is required.

The following inspection and tests are suggested: vacuum, pH, consistency, aroma, colour, detinning of can, enamel failure, swollen cans, seam evaluation, gas production.

Incubation test records will enable the identification and segregation of spoiled products. They must include the date of production, the shift or hour, the machine line number, processing time and temperature, incubation time and temperature, results of the various post incubation tests. The records shall be retained at least as long as the production date or a minimum of three years.

1.13.16.01 Thermal Process Control Records

This task assesses the availability and completeness of all thermal process records. Many other tasks contain "record assessment" If records for a particular task are not satisfactory, assess the particular task as "unsatisfactory". The evaluation of this task will be based on the adequacy of records not evaluated elsewhere.

Complete records shall include all inputs to or components of the process. For example, the scheduled process including heat distribution tests, container closure records, specific processing records, water quality records and process deviation records.

It is important that scheduled processes be properly established, correctly applied, sufficiently supervised and documented to provide positive assurance that the requirements have been met. These assurances apply also to the seaming and sealing operations. For practical and statistical reasons, an end-product analysis by itself is not sufficient to monitor the adequacy of the scheduled process.

Processing and Production Records

Permanent, legible and dated records of time, temperature, codes and other pertinent details shall be kept concerning each retort load or code lot for continuous retorts or aseptic processes. Such records are essential as a check on processing operations and will be invaluable if some question arises as to whether a particular lot had received adequate heat processing. These records shall be made by the retort or processing system operator or other designated person, on forms which shall include: product name and style, the code lot number, the retort or processing system and recorder chart identification, the container size and types, the approximate number of containers per code lot interval, the minimum initial temperature, the scheduled and actual processing time and temperature, the recorder-controller and indicating thermometer readings, and other appropriate processing data.

Deviation in Thermal Processing

Whenever the in-process monitoring records, processor check or other means disclose that a low-acid food or container system has received a thermal or sterilization treatment less than that stipulated in the scheduled process, the processor shall:

  1. Identify, isolate and then reprocess to commercial sterility or destroy that part of the code lot or lots involved. Complete reprocessing records shall be retained; or
  2. Isolate and retain that part of the code lot or lots involved to permit further detailed evaluation of the heat processing records. Such evaluation shall be made by competent processing experts in accordance with procedures recognized as being adequate to detect any hazard to public health. If this evaluation of the processing records demonstrates that the product has not been given a safe thermal treatment, the product isolated and retained shall be either fully reprocessed to render it commercially sterile or suitability disposed of under adequate and proper supervision to assure the protection of the public health. A record shall be made of the evaluation procedures used, the results obtained and the actions taken on the product involved.

In the case of a stoppage of continuous agitating retorts emergency scheduled processes may be established to permit compensation for temperature deviations, not to exceed 5°C (10°F).

1.13.17.01 Certified Operator

It is a regulatory requirement that thermal processing be carried out under the continuous supervision of a person who has attended a course in thermal processing and has received a certificate of competence on completion of the course.

1.13.18 Coil Vat

When a coil vat is used for pasteurizing cream for butter-making, it must be pasteurized at the legal pasteurization temperature and time as specified by provincial regulations. Any coil vats used to pasteurize ice cream mix or other dairy products must be rated under the batch pasteurization tasks.

1.13.18.01 General Conditions

Coil vats shall be constructed of stainless steel and be in good mechanical and sanitary condition. Sanitary seal assemblies at the shaft ends should be of the removable type and cleaned daily. Old style equipment without sanitary seals will be accepted if the packing glands are maintained and operated without adverse effects. All new units must be provided with removable sanitary seals. Vat liner, coils, centreboard, covers, outlet valve, fittings and exterior surfaces must be clean and in good condition.

1.13.18.02 Critical Controls

For control of pasteurization by coil vats, the vats shall be equipped with an indicating and a recording thermometer. Recording charts shall be marked to show all the required information to assess if proper pasteurization occurred for all applicable products.

For those plants that do not have a recording thermometer, it is the responsibility of the plant personnel to prove that the product is properly pasteurized. One method would be to conduct a phosphatase test on the cream for each day's production (if more than one vat is produced a day, a composite test to include cream from each vat could be done).

All new units must have a recording thermometer.

No product shall be added to the vat after the beginning of the hold period and the product shall not be removed before the hold period is completed.

The air space temperature above the product must be at least 3°C (5°F) higher than the minimum required temperature of pasteurization during the holding period. This could be accomplished by installing an air space heater or elevating the pasteurizing temperature.

Each pasteurizing coil vat must be equipped with an air space indicating thermometer. Coil vats that are not equipped with an air space indicating thermometer may be rated as satisfactory if a phosphatase test is done to verify the product has been properly pasteurized. All new units must be equipped with an air space indicating thermometer.

Vat covers may be open while cream is being heated. However, covers must be closed prior to the holding period to assure proper pasteurization of the air space during the holding time. Covers must be kept closed during the holding and cooling period.

1.13.18.03 Records

Process control records should be part of the quality assurance program. This information must be recorded in pen to provide a permanent record. Since this information provides a processing record, it will assist the plant in tracking down quality and safety problems and prevent recall of their products. As these records are the only historical record of exact happenings of the pasteurization of each product it is very important that the records adequately and accurately reflect the heating process. It is acceptable for some information that is required on the process control record to be in a separate document, for example a computer print-out as long as there is a cross reference by production code and/or date between the print-out and the process control record. The process control record must be replaced daily. It is also critical that the operator notes any unusual occurrences, reasons for and time of occurrence. The process control record is the legal record of the pasteurization process. The process control record(s) must be reviewed on a timely basis by a designated person responsible to the plant management.

Process control records for the coil vats shall provide the following data for every batch:

  1. Plant name and address or registration number
  2. Date, shift and batch number where applicable
  3. Vat number
  4. Record of the holding period
  5. Reading of air-space thermometer at the start of the holding period at a given time or reference point indicated on the chart and at the end of the holding period
  6. Reading of the indicating thermometer during the holding period at a particular referenced reading point on the chart
  7. Amount and name of the product pasteurized (when more than one product is pasteurized)
  8. Operator's comments and reasons for all unusual occurrences
  9. Signature or initials of the operator

If required to do phosphatase test (either on the cream or the butter) the following records must also be kept:

  1. Results of the phosphatase test for each day's production (composite sampling is acceptable)
  2. Temperature of pasteurization for each vat
  3. Holding time of pasteurization for each vat
  4. Signature of the responsible person

1.13.19 Formulation and verification

This task will evaluate the safety of:

  1. Process cheeses - produced with the aid of heat
  2. Cold pack cheeses - produced without the aid of heat
  3. Sweetened Condensed Milk
  4. Aerosol packaged products

Processed cheese products with pH above 4.6 and water activity above 0.85 in hermetically sealed containers are considered as low-acid foods. Therefore, they must be commercially sterile (microbiologically stable) if kept at ambient temperature (e.g. non-refrigerated processed spreads). If the processed cheese product is not commercially sterile it must be refrigerated (4°C or below) and appropriately labelled.

Two criteria affect the safety of process cheeses: heat treatment and formulation control. The heat treatment liquefies the product and destroys vegetative cells but not the viable spore-forming bacteria (may be pathogenic) of genus Clostridia and Bacillus. These spore-forming bacteria can cause defects in processed cheese by producing gas with or without off-odours. Proper product's formulation will create a difficult environment for spore-forming bacteria to germinate and therefore produce a commercially sterile product.

The manufacture of sweetened condensed milk is similar to that of evaporated milk. The milk is not sterilized and crystallization is controlled by cooling. The extended shelf life of sweetened condensed milk is derived not from thermal processing, but from the reduced water activity level resulting from the high solute concentration (40 to 45% sugar). The water activity is sufficiently low to inhibit growth of many bacteria, other micro-organisms, especially yeasts and moulds are able to develop.

Aerosol packaged products (e.g. whipped cream) are derived from cream that is Ultra-High Temperature processed, aseptically filled and pressurized by a suitable gas permitted as a propellant. Criteria that affect the safety of these products include heat treatment, formulation and manufacture control.

1.13.19.01 Product Analysis

1. Process Cheeses

Process cheeses are characterized essentially by composition, water content and consistency. The three main groups are processed cheese, process cheese food and process cheese spread:

Processed cheese is a blend of fresh and natural aged cheeses which have been shredded and mixed. Disodium phosphate or sodium citrate is added as an emulsifying agent, and the blend is heated, packaged and cooled, after which no further ripening occurs. The blend may consist of one or two or more varieties of natural cheese and may contain pimentos, fruits, vegetables, or meats. Smoked cheese or smoked flavour may also be added. A typical composition is 50.5% milk-fat-in-solids and 39.5% moisture. Process cheese food is prepared similarly, except that it contains less cheese, with nonfat dry milk, or whey solids and water added. This results in a lower milk fat content and more moisture than in process cheese. Process cheese food must contain not more than 46% moisture and not less than 23% milk fat by Dairy Products Regulations. Process cheese spread contains even more moisture and the milk fat content is usually lower. By Dairy Products Regulations it must contain not more than 60% moisture, and not less than 20% milk fat. A stabilizer such as carob bean gum or sodium alginate is used in the preparation of this product to prevent separation of ingredients.

2. Coldpack Cheeses

Coldpack cheese or Club cheese is the blend of the same or two or more varieties of fresh and aged natural cheese, as in process cheese, except that the cheese is mixed into a uniform product without heating. It may have a smoked flavour. The Dairy Products Regulations are specific with respect to milk fat and moisture content depending upon the variety or blend of cheese used.

Since cold pack cheeses are not heat treated, nor do they contain bacteriostatic emulsifiers, they will contain viable microorganisms and therefore are not shelf stable.

3. Sweetened Condensed Milk

Sweetened condensed milk may be made from either whole or skim milk. The milk is preheated and, in some cases, superheated, before passing to the evaporator. Sugar (usually sucrose) or other sugars, may be dissolved in the preheated milk before evaporation or during the later stages of evaporation. The concentration of sugar in water is expressed as the sugar ratio (sucrose in aqueous phase) and may be calculated as:

sugar ratio = % sugar in condensed milk x 100
Divided by 100 - total solids in condensed milk

The sugar ratio is usually 63.5 to 64.5 for retail product, but can be as low as 42 for bulk, whole milk product to be stored under refrigeration. Sweetened condensed milk is not sterile and while the reduced water activity level is sufficiently low to inhibit growth of many bacteria, other microorganisms are able to develop.

4. Aerosol Packaged Products

Stabilizers are a necessary component in the product formulation as well as the use of a suitable gas permitted as propellant necessary to pressurize the container. These propellants exist partly as a vapour in the headspace and partly as a liquid layer on top of the cream. Dispensing thus occurs at constant pressure but the contents must first be shaken to from an emulsion. On release of pressure, cream is propelled through the outlet valve. The propellant volatilizes to form a whipped structure of high overrun; a specially shaped outlet nozzle permits the cream to be piped directly. The whip becomes less stable and shrinkage occurs on storage.

1.13.19.02 Product Formulation

Processed cheeses (includes processed cheese, process cheese food and process cheese spread)

The germination of spore-forming bacteria after heat processing of process cheeses is prevented by controlling the following factors:

  1. Blend composition
  2. Sodium chloride concentration
  3. Type and concentration of emulsifying agent
  4. Water level
  5. pH
  6. Absence of natural inhibitors
  7. Prior treatment of condiments, that is to say, irradiation treatment, heat sterilization

Therefore, to keep processed cheese microbiologically safe after the heat treatment, the following guidelines may be used:

  1. pH not to exceed 5.6 (lower pH values increase safety)
  2. Moisture level not to exceed 60% (lower the moisture, the safer the product becomes)
  3. Emulsifiers (sodium, potassium and calcium salts of the mono, di and polyphosphoric acids; sodium, potassium and calcium salts of citric acid; citric acid and/or phosphoric acid with sodium hydrogen carbonate and/or calcium carbonate) concentration not to exceed 4% in total or 3.5% measured as anhydrous salts
  4. Moisture content and pH have an inverse relationship within a narrow range, that is to say, for higher moisture contents lower pH's must be used and vice-versa (see Appendix 8  -  processed cheese microbiological stability chart for non-refrigerated products). If the product doesn't fall within the range an explanation would have to occur on a case by case basis to evaluate the safety of the product
  5. Water activity not to exceed 0.94.
  6. If new ingredients or changes in the processing conditions are introduced, a new safety study should be conducted as per task 1.10.07.02 Manufacturing/Allergen Controls and Records.

Microbial growth for both sporeformers and non-sporeformers should not occur in process cheese. Any microbial growth (e.g. mesophilic non-sporeforming, mould) is evidence of lack of sterility and therefore the plant must investigate the problem.

Sweetened Condensed Milk

Sweetened condensed milk is subject to spoilage by osmotolerant yeasts, notably Torulopsis. The organism enters the milk after preheating, generally due to poor plant hygiene. The growth of the organism is slow, especially at lower ambient temperatures, but sufficient gas may be produced to swell the cans. Growth of moulds, usually species of Aspergillus and Penicillium, on the upper surface of the milk leads to the formation of "buttons", small aggregates of mycelium and coagulated casein. The presence of mould is accompanied by off-flavours due to proteolysis. The reason for this is poor plant hygiene which can be further exaggerated by a large head space containing sufficient oxygen for excessive growth.

Most bacteria are unable to grow, but spoilage occasionally occurs, especially when there is a low sugar content. The relatively osmotolerant Micrococcus and Bacillus are most common. Typical spoilage patterns involve thickening, acid production, proteolysis, and in full cream products, lipolysis.

Aerosol Packaged Products

Cream based products have been associated with Listeria monocytogenes, Bacillus spp. and Staph aureus, due to in most cases post processing contamination, poor hygiene or inadequate heat treatment or failure in the packaging system.

1.13.19.03 Processing Controls

1. Processed Cheeses

Cookers are used in the manufacture of processed cheese. This operation is carried out in cookers which are jacketed heated kettles which may be closed with hydraulically operated lids or manually or in a continuous cookers consisting of a battery of stainless steel tubes.

For most process cheeses the product's formulation and the cooking step assures the safety and quality of the product. Therefore the heat processing step must be well documented and well controlled.

The record of the cooking may be generated manually or electronically. It is important, however, that the computerized system meets the minimum criteria of the conventional system. In the case of the conventional recording chart the unit shall be sealed to provide tamper evident restricted access to prevent adjustment by unauthorized personnel. In the case of the computerized system access to the computer must also be protected in some manner to prevent adjustment by unauthorized personnel. The operator must have control of the cooking process. The operator must validate the indicating thermometer temperature to the recording chart during and at the end of heating time as measured by the indicating thermometer.

The recording chart information is part of the quality assurance program and must provide the following information:

  1. Plant name or number
  2. Product name
  3. Batch number
  4. Corresponding indicating thermometer temperature during and at the end of heating time
  5. Signature or initials of operator

2. Coldpack Cheeses

In order to improve microbiological safety the following measures must be taken:

  1. Coldpack cheeses must be kept refrigerated (4°C or below) and be appropriately labelled
  2. A raw product quality control program must be in place
  3. Good manufacturing practices are required e.g. clean equipment and environment, personnel hygiene and practices etc.

3. Sweetened Condensed Milk

It is necessary to apply stringent control both of general hygiene and of specific operations and detailed measures should be incorporated into master manufacturing schedules. By implementing proper controls during pre-heating, storage (cooling), the time when the sugar is added, and effective protection against environmental contamination between the evaporation and canning stages, problems can be avoided. Special account should be taken of the viscous nature of sweetened condensed milk and cleaning schedules adjusted accordingly.

4. Aerosol Packaged Products

By implementing proper controls in conjunction with good formulation control, the proper levels of stabilizers and effective pressurization of the container will ensure microbiological safety. End product testing which includes chemical testing for correct fat content and microbiological testing is necessary to ensure satisfactory processing and handling.

1.13.20 Heat Exhanger

1.13.20.01 Heat Exchanger

Heat exchangers are widely used in the dairy processing industry for fore-warming or cooling the milk product and for cooling cheese brine. The requirements for this task apply to all such systems. They are designed to transfer heat from a hot liquid to a cold liquid. This equipment must be regularly monitored under an equipment maintenance program to minimize contamination risks. Most heat exchangers are one of the following types.

Spiral type: These are tubular type preheaters which are fully enclosed inside the tube chests or inside milk vapour areas. These systems are impossible to inspect inside, therefore a check on the plant's cleaning program is essential.

Surface cooler type: In this system milk is distributed over the cooling coils by means of a distributor pipe or trough and the milk drops from the lower coil into a collecting trough. Product is exposed to air in this system therefore, subjecting the product to air-borne contamination.

Tubular type: These heat exchangers consist of a small tube mounted concentrically within a larger tube. Product is pumped through the inner tubes, entering at the low point and leaving at the high point while the heating or cooling medium enters the larger tube at the high point and flows through the space between tubes, leaving at the bottom. The system is designed to keep the two mediums separate. The pressure must be monitored and recorded daily to ensure that the pressure is higher on the milk product side than the medium side. The pressure on the milk product side must be at least 14 kPa (2 psi) higher than the medium side. Cleaning without daily dismantling is a satisfactory practice when an effective cleaning program is established.

Plate type: These heat exchangers consist of a number of stainless steel plates, sealed at the edges with gaskets, and are clamped tightly within a press. The spaces between the plates are occupied alternatively by milk and the heating or cooling medium. The system is designed to keep the two mediums separate. The pressure must be monitored and recorded to ensure that the pressure is higher on the milk product side than the medium side. The pressure on the milk product side must be at least 14 kPa (2 psi) higher than the medium side.

A routine program to monitor the condition of plates (pin holes in plates, gasket condition, cracks, etc.) must be established by plants, taking into consideration the design specifications, operating conditions and hours of operation, wear and the history of the plates and gaskets. The integrity of all food contact heat exchange surfaces must be checked at least once per year by an acceptable method (e.g. dye recirculation, dye check, pressure retention, etc.). However, if the plant has experienced problems with heat exchanger integrity (plate or gasket issues), a more frequent inspection program must be implemented to verify that the problem has been remedied. Appropriate records must be kept to show proper testing has occurred. These records should also document the cause of any failure (e.g. age, compression, metal fatigue, etc.). If pin holes are found in any plate in any section then all plates in the same section should be checked. If inspection reveals that the plates are dirty then the exchanger must be opened daily for inspection and hand cleaned until an adequate cleaning program has been established.

If the product passing through the heat exchanger is pasteurized finished product an automated mechanism is the best way to achieve the correct pressure relationship in the cooling section during forward flow, divert and shutdown conditions, so that the pressure on the cooling media side is not greater than that of the pasteurized product at all times. Where there is an automatic mechanism the cooling medium supply shall be stopped or diverted and the cooling medium side vented to atmosphere in the following cases:

  1. During forward flow, when the product pressure on the pasteurized product side drops to within 2 psi of the cooling medium side of the plates and
  2. During diverted flow and shutdown conditions

If a product vacuum breaker is in use, the venting of the cooling medium side shall be at an elevation below that of the product vacuum breaker. To satisfy the above requirement, the control mechanism must be demonstrable to the regulatory authority.

In systems where there is not an automated mechanism and the product passing through the heat exchanger is pasteurized finished product then the establishment must have a written program which includes the person responsible, what is to be done, how it is to be done, how often it is done (frequency), records to be kept and results of monitoring, verification procedures (both on-site and record review), and actions taken for deviant situations. The program must specify the parameters of acceptability/unacceptability and defines the preventative measures taken to prevent the re-occurrence of deviations. The program must include at a minimum:

  1. Records of the pressures recorded a minimum of twice a day during production, at beginning and end of run
  2. Microbial cooling media checks (e.g. psychrotrophs, coliforms) at a frequency of at least once per week
  3. pH testing of cooling media at a frequency of at least once per week
  4. Visual cooling media check at least once per week
  5. Pinhole testing and plate teardowns at a minimum of once every six months
  6. Plate replacement program

In the event that the written program does not adequately address the risks or there is failure to implement or follow the program then it will be mandatory for the plant to install an automated mechanism.

Note: Exemptions to the requirement for an automatic mechanism or written program include:

  1. Where product being cooled is raw product which will ultimately be pasteurized
  2. Where potable water being used as the coolant is non-recirculated
  3. Tubular type heat exchangers

It is critical that W1 additives (dairy safe and approved) are being used in the cooling media where there is no automated mechanism.

Date modified: