Dairy Establishment Inspection Manual – Chapter 18
A. Thermometers

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Test 1: Indicating Thermometers - Temperature Accuracy

Application:

Pasteurization and airspace indicating thermometers. Applies to HTST, Batch, APPS and HHST systems.

Frequency:

  1. Upon installation and once every 6 months thereafter.
  2. Whenever the seal on a digital sensor or a digital control box has been broken and the reason for the breaking of the seal may have an effect on the sensing element. All incidences of a broken seal must be recorded in the log book of seal control and replacement or as noted by the equipment calibrator.

Criteria:

  1. Pasteurization indicating thermometer: accuracy within 0.25°C (0.5°F) in a specified scale range.
  2. Airspace indicating thermometer: accuracy within 0.5°C (1°F) in a specified scale range.

Apparatus:

  1. A certified test thermometer meeting the specifications of Appendix 18 - 1 - Testing Apparatus Specifications.
  2. Water, oil or other suitable media and agitator.
  3. Suitable means of heating water, oil or other suitable media bath.
  4. Indicating thermometer to be tested.

Method:

Both the indicating and test thermometers are exposed to water, oil or other suitable media bath of uniform temperature. Indicating thermometer reading is compared to the reading of the test thermometer.

Procedure:

  1. Bring up the water, oil or other suitable media bath temperature to within a range of 2°C of the appropriate pasteurization (diversion) temperature, airspace temperature or aseptic processing temperature.
  2. Maintain rapid agitation throughout the test.
  3. Insert the indicating and test thermometer to indicated immersion point during the test. Hold the indicating and certified thermometer for five minutes, two minutes for electronic recording thermometers, before reading.
  4. Compare both thermometer readings at the temperature reading within the test range and record results and thermometer identification.
  5. Repeat the test 3 times.
  6. Record the results.

Corrective Action:

Do not run test if mercury column has been split or capillary tube is broken, as thermometer should be returned to the factory for repair. When the indicating thermometer differs from the test thermometer by more than 0.25°C (0.5°F) and the airspace thermometer by more than 0.5°C (1°F), the scale plate of the indicating thermometer should be adjusted to agree with the test thermometer. Retest the thermometer after adjustment.

Note: The above procedure applies only to thermometers used for pasteurization. All other thermometers used in the establishment should be calibrated according to the manufacturer's recommendations.

Test 2:  Indicating Thermometers - Thermometric Response

Application:

Pasteurization indicating thermometer. Applies to HTST systems.

Frequency:

Upon installation and once every 6 months thereafter.

Criteria:

Indicating thermometer moves through a 7°C (12°F) range in no more than four (4) seconds.

Apparatus:

  1. Test thermometer.
  2. Stopwatch.
  3. Water, oil or other suitable media bath and agitator.
  4. Suitable means for heating the water, oil or other suitable media bath.
  5. Indicating thermometer from pasteurizer.
  6. Bucket of ice water

Method:

Measure the time required for the reading of the thermometer being tested to increase 7°C (12°F) through a specified temperature range (temperature range must include pasteurization or treatment temperature). The temperature used in the water, oil or other suitable media bath will depend upon the scale range of the thermometer to be tested.

Procedure:

  1. Immerse the indicating thermometer in water, oil or other suitable media bath held at a temperature at least 11°C (19°F) higher than the minimum scale reading on the indicating thermometer. The bath temperature should be higher than the maximum pasteurization temperature for which the thermometer is used.
  2. Immerse indicating thermometer in bucket of ice water for 10 seconds to cool it.
    Note: Continuous vigorous agitation of water, oil or other suitable media baths during the performance of steps 3, 4 and 5 is required. Elapsed time between end of step 1, and beginning of step 3 should not exceed 15 seconds so hot water does not cool significantly.
  3. Insert indicating thermometer in hot water, oil or other suitable media bath to proper bulb immersion depth.
  4. Start stopwatch when indicating thermometer reads 11°C (19°F) below bath temperature.
  5. Stop stopwatch when indicating thermometer reads 4°C (7°F) below bath temperature.
  6. Record the thermometric response time (must be less than 4 seconds).
  7. Repeat the test three times.
  8. Record the results.

    Example: For a thermometer used at pasteurization temperature set points of 71.7 and 74.4°C (161 and 166°F), a water, oil or other suitable media bath at a temperature of 78.3°C (173°F) could be used. 11°C (19°F) lower than 78.3°C (173°F) water, oil or other suitable media bath would be 67.3°C (154°F); 4°C (7°F) lower than 78.3°C (173°F) water, oil or other suitable media bath would be 74.3°C (166°F). Hence, after immersing the thermometer which has been previously cooled, in the 78.3°C bath (173°F), the stopwatch is started when thermometer reads 67.3°C (154°F) and stopped when it reads 74.3°C (166°F).

Note: The test included the pasteurization temperature of 71.7 and 74.4°C (161 and 166°F).

Corrective Action:

If the response time should exceed 4 seconds, the thermometer should be replaced or returned for repair.

Test 3:  Recording Thermometers - Check Against Indicating Thermometer

Application:

All recording and recording/controller thermometers used to record milk temperatures during pasteurization. Applies to HTST Batch, APPS and HHST systems.

Frequency:

Upon installation, once a year (6 months for APPS) and daily by the plant operator.

Criteria:

Recording thermometer shall not read higher than corresponding indicating thermometer.

Apparatus:

  1. Certified or calibrated indicating thermometer.
  2. Water, oil or other suitable media bath and agitator.
  3. Suitable means to heat the water, oil or other suitable media bath.

Method:

This test requires that a reading of the recording thermometer be compared with that of the indicating thermometer at a time when both are exposed to milk at a stabilized pasteurization temperature while the pasteurization system is operating and both thermometers are installed in their normal location in the temperature sensing chamber.

Procedure A: Annual Test

  1. Place the indicating or certified thermometer and recorder probe in a circulating water, oil or other suitable media bath at processing temperature. Stabilize for five minutes (two minutes for electronic recording thermometers).
  2. Read the indicating and recording thermometer. Record the results.
  3. Adjust the recording pen to the same as the indicating thermometer if needed.

Procedure B: Daily Test

  1. Read the indicating thermometer when the milk is at a stabilized temperature for 5 minutes (two minutes for electronic recording thermometers).
  2. Immediately inscribe a line using permanent ink on the recording thermometer chart that intersects the recording temperature arc at the pen location.
  3. Record on the chart the indicating thermometer temperature and initials of the operator or person performing the test.
  4. Record results and make adjustments if required.

Corrective Action:

If the mercury-activated thermometer or recorder-controller thermometer reads higher than the indicating thermometer, the pen or temperature adjusting mechanism should be adjusted. Re-test the thermometer after adjustment.

If the digital recording thermometer or recorder-controller thermometer reads higher than the indicating thermometer, the recording temperature arm should be adjusted to agree with the indicating thermometer if the recorder-controller arm is equipped with an adjustment. Re-test the thermometer after adjustment.

In cases where the recorder-controller thermometer arm cannot be adjusted (i.e. the recorder chart is digitally transcribed and there is no recorder arm), then the recording thermometer would need to be re-calibrated and adjusted using Procedure A. The details of the recorder-controller deviation and the corrective action must be documented.

Note: The above procedure applies only to recording thermometers used for pasteurization. All other recording thermometers used in the establishment should be calibrated according to the manufacturer's recommendations.

Test 4: Recording Thermometer - Time Accuracy

Application:

All recording and recorder/controller thermometers used to record time of pasteurization. Applies to HTST, Batch, APPS and HHST systems.

Frequency:

Upon installation and at least once a year (6 months for APPS) thereafter.

Criteria:

The recorded time of pasteurization shall not exceed true elapsed time.

Apparatus:

Stopwatch.

Method:

Comparison of the recorded time over a period of not less than 30 minutes with a stopwatch of known accuracy. For recorders utilizing electric clocks, check cycle on face plate of clock with known cycle; observe that clock is in operating condition.

Procedure:

  1. Determine if chart is appropriate to recorder. Verify that mechanism to grip and perforate chart paper is operational.
  2. Mark a reference point on the backplate of the recorder at the outer circumference of the chart paper.
  3. With the chart paper removed from the recorder, inscribe a reference mark at the outer edge of the chart, lined up with any printed hour time line.
  4. Install chart in the recorder with reference mark on chart lined up exactly with reference mark on back plate. Secure in place.
  5. Start stopwatch.
  6. At the end of 30 minutes by stopwatch, inscribe a second reference mark on the chart paper exactly opposite the backplate reference mark.
  7. Stop the stopwatch.
  8. Compare the time recorded on the chart with the true elapsed time from the stopwatch.
  9. For electric clocks, remove face plate; compare cycle specification on face plate with current cycle utilized.
  10. Enter finding on chart and initial.
  11. Record results.

Corrective Action:

If recorded time is incorrect the clock should be adjusted or repaired.

Note: The above procedure applies only to recording thermometers used for pasteurization. All other recording thermometers used in the establishment should be tested according to the manufacturer's recommendations.

Test 5: Recording Thermometer - Temperature Accuracy

Application:

All recording and recorder/controller thermometers used to record milk temperatures during pasteurization. Applies to HTST, Batch, APPS and HHST systems

Frequency:

Upon installation, at least once a year (6 months for APPS) and whenever recording pen-arm setting requires frequent adjustment.

Criteria:

Accuracy within ±0.5°C (1°F), in specified scale range. Batch pasteurizers used solely for thirty (30) minute pasteurization of milk or milk products at processing temperatures above 71°C, the recording thermometers shall be accurate to within ±1°C (±2°F).

Apparatus:

  1. Verified pasteurizer indicating thermometer.
  2. Three water, oil or other suitable media baths and agitator.
  3. Suitable means for heating the water, oil or other suitable media bath.
  4. Ice.

Method:

The testing of a recording thermometer for temperature accuracy involves the determination of whether or not the temperature pen-arm will return to within 0.5°C (1°F) or within 1°C (2°F) as provided above, of its previous setting after exposure to boiling water and melting ice.

Procedure:

  1. Heat a container of water to pasteurization temperature.
  2. Adjust the recording pen to read exactly as the previously tested indicating thermometer after a stabilization period of 5 minutes (2 minutes for electronic recording thermometers) at pasteurization temperature. The water, oil or other suitable media shall be rapidly agitated throughout the stabilization period.
  3. Prepare one water, oil or other suitable media bath by heating to the boiling point. Maintain temperature. Prepare a second bath with melting ice. Place baths within working distance of the recorder sensing element.
  4. Immerse the sensing element of recorder in boiling water, oil or other suitable media for not less than 5 minutes (2 minutes for electronic recording thermometers)
  5. Remove the sensing element from the boiling water, oil or other suitable media and immerse it in the water, oil or other suitable media heated to pasteurization temperature. Allow a 5 minute (2 minutes for electronic recording thermometers) stabilization period for both indicating or certified and recording thermometers. The two readings must be within ±0.5°C (1°F) or ±1°C (2°F) as provided above. The water, oil or other suitable media shall be rapidly agitated throughout the stabilization period.
  6. Remove sensing element from the bath at operating temperatures and immerse in melting ice for not less than 5 minutes (2 minutes for electronic recording thermometers).
  7. Remove sensing element from ice water and immerse in water at pasteurization temperature. Allow 5 minute (2 minutes for electronic recording thermometers) stabilization period for both indicating or certified and recording thermometers. The two readings must be within ±0.5°C (1°F) or ±1°C (2°F) as provided above. The water, oil or other suitable media bath shall be rapidly agitated throughout the stabilization period.
  8. Record results.

Corrective Action:

If the recording pen does not return to ±0.5°C (1°F) or ±1°C (2°F) as provided above, of indicating thermometer reading, the recording thermometer should be repaired or replaced as necessary.

Note: The above procedure applies only to recording thermometers used for pasteurization. All other recording thermometers used in the establishment should be tested according to the manufacturer's recommendations.

Test 6: Milk-Flow Controls - Milk Temperatures at Cut-In and Cut-Out

(A) Installation and Inspection Test

Application:

All Safety Thermal Limit Recorders used in connection with HTST pasteurizers.

Frequency:

Upon installation and once every 6 months there after and whenever the seal on the sensing element of the recorder-controller is broken and the reason for the breaking of the seal may have an effect on the sensing element. All incidences of a broken seal must be recorded in the log book of seal control and replacement or as noted by the equipment calibrator.

Criteria:

  1. No forward flow until pasteurization temperature has been reached.
  2. Flow diverted before temperature drops below minimum pasteurization temperature.
  3. Cut-in temperature is higher than cut-out temperature.

Apparatus:

  1. Water bath.
  2. Indicating or Certified test thermometer with accuracy of ±0.1°C (0.2°F) as determined by the National Bureau of Standards.
  3. Water bottle.

Method:

Observe the actual temperature of the indicating thermometer at the instant forward flow starts (cut-in) and stops (cut-out).

Procedure:

1. Cut-in temperature
  1. While water in water bath is completely flooding the sensing element of the Safety Thermal Limit Recorder and the indicating or certified thermometer, increase the heat gradually so as to raise the temperature of the water or milk at a rate not exceeding 0.5°C (1°F) every 30 seconds.
  2. Observe the verified indicating or certified thermometer reading at the instant the Flow Diversion Device starts to move.
  3. Observe that the frequency pen reading is synchronized with the recording pen on the same reference arc.
  4. Record the indicating or certified thermometer reading.
2. Cut-out temperature
  1. After the cut-in temperature has been determined and while the water is above the cut-in temperature, allow the water to cool slowly at a rate not exceeding 0.5°C (1°F) per 30 seconds. Cool water in a water bottle may be used if necessary.
  2. Observe indicating or certified thermometer reading at the instant forward flow stops.
  3. Record the indicating or certified thermometer reading.

(B) Daily Test

Application:

All Safety Thermal Limit Recorders used in connection with HTST pasteurizers.

Frequency:

Daily by the plant operator, whenever a new set-point is selected on a multiple temperature divert unit and whenever the seal on the recorder/controller is broken. All incidences of a broken seal must be recorded in the log book of seal control and replacement or as noted by the equipment calibrator.

Criteria:

  1. No forward flow until pasteurization temperature has been reached.
  2. Flow is diverted before temperature drops below minimum pasteurization temperature.
  3. Cut-in temperature is higher than cut-out temperature.

Apparatus:

None.

Method:

Observe the actual temperature of the indicating thermometer at the instant forward flow starts (cut-in) and stops (cut-out).

Procedure:

1. Cut-in temperature
  1. With the system operating and while milk or water is completely flooding the sensing element of the Safety Thermal Limit Recorder and the indicating thermometer within the sensing chamber, increase the heat gradually so as to raise the temperature of the water or milk at a rate not exceeding 0.5°C (1°F) every 30 seconds.
  2. Observe the indicating thermometer reading at the instant the Flow Diversion Device begins to move.
  3. Observe that the frequency pen reading is synchronized with the recording pen on the same reference arc.
  4. Record the indicating thermometer reading on the recorder chart; inscribe initials.
2. Cut-out temperature
  1. After the cut-in temperature has been determined and while the milk or water is above the cut-in temperature, allow the milk or water to cool slowly at a rate not exceeding 0.5°C (1°F) per 30 seconds.
  2. Observe indicating thermometer reading at the instant forward flow stops.
  3. Record the indicating thermometer reading on the recorder chart; inscribe initials.

Corrective Action:

If the reading is below the minimum pasteurization temperature, the cut-in and cut-out mechanism and/or the differential temperature mechanism should be adjusted to obtain proper cut-in and cut-out temperatures by repeated tests.

Test 6.1: Milk-Flow Controls - Milk Temperatures - Cut-In and Cut-Out HHST Pasteurizers and APPS Using Indirect Heating

Application:

All HHST pas­teuriz­ers and APPS using indirect heating. When testing aseptic processing systems, the "product divert system" or product divert valve or acceptable control system may be substituted for the flow diversion device when it is referenced in this test.

Frequency:

Upon installation, and every 6 months there after and whenever the thermal controller seal is broken and the reason for the breaking of the seal may have an effect on the sensing element. All incidences of a broken seal must be recorded in the log book of seal control and replacement or as noted by the equipment calibrator.

Criteria:

  1. No forward flow unless pasteurization or aseptic processing temperature has been achieved.
  2. Product flow diverted at a temperature lower than the chosen pasteurization or aseptic processing standard (i.e. that which is established by the scheduled process, where Fo=3.0 as a minimum).

Apparatus:

Oil bath (above boiling point).

Method:

Observe the actual temperature in the constant temperature bath at which the two sensing elements (holding tube and flow diversion device) signal for forward flow (cut-in) and diverted flow (cut-out).

Procedure:

1. Cut-in temperature
  1. Wire the test lamp in series with the control contacts of the sensing element (holding tube). Immerse this sensing element in the constant temp­erature bath. Raise the bath temperature at a rate not exceeding 0.5°C (1°F) every 30 seconds.
  2. Observe the temperature reading at the cut-in temperature (when the test lamp lights).
  3. Record the temperature.
  4. Repeat the procedure for the other sensing element, i.e. the flow-diversion device.
2. Cut-out temperature
  1. After the cut-in tempera­ture has been determined and while the oil is above the cut-in temperature, allow the oil to cool slowly at a rate not exceeding 0.5°C (1°F) per 30 seconds.
  2. Observe the temperature reading on the controller when the test lamp goes out (cut-out temperature).
  3. Determine that the cut-out temperature on the thermal limit controller is equivalent to or above the chosen pasteurization or aseptic processing standard (i.e. that which is established by the scheduled process, where Fo= 3.0 as a minimum).
  4. Record the temperature.
  5. Repeat the procedure above for the other sensing element, i.e., the flow diversion device.
  6. When proper cut-out tempera­ture has been verified for both sensing elements, seal the controller system.

Corrective action:

Where adjustment is necessary, refer to manufacturer's instructions. After adjust­ment, repeat the procedure above.

Test 6.2: Milk-Flow Controls - Milk Temperatures - Cut-In and Cut-Out HHST Pasteurizers and APPS Using Direct Heating

Application:

All HHST pas­teurizers and aseptic processing systems using direct contact heating. When testing aseptic processing systems, the "product divert system" or product divert valve" or "acceptable control system" may be substituted for the "flow-diversion device" when it is referenced in this test.

Frequency:

Upon installa­tion, and every 6 months there after; when­ever the thermal limit controller seal is broken.

Criteria:

  1. No forward flow unless pasteurization or aseptic processing temperature has been achieved.
  2. Product flow diverted at a temperature lower than the chosen pasteurization or aseptic processing standard (i.e. that which is established by the scheduled process, where Fo=3.0 as a minimum).

Apparatus:

Oil bath (above boiling point).

Method:

Ob­serve the actual temperature in the constant temperature bath at which the two sensing elements (holding tube and flow diversion device) signal for forward flow (cut-in) and diverted flow (cut-out).

Procedure:

1. Cut-in temperature
  1. Wire the test lamp in series with the control contacts of the sensing element (holding tube). Immerse this sensing element in the constant temp­erature bath. Raise the bath temperature at a rate not exceeding 0.5°C (1°F) every 30 seconds.
  2. Observe the temperature reading on the controller when the test lamp lights (cut-in temperature).
  3. Record the temperature.
  4. Repeat the procedure for the other two sensing elements, i.e. the vacuum chamber and the flow diversion device.
2. Cut-out temperature
  1. After the cut-in tempera­ture has been determined and while the oil is above the cut-in temperature, allow the oil to cool slowly at a rate not exceeding 0.5°C (1°F) per 30 seconds.
  2. Observe the temperature reading on the controller when the test lamp goes out (cut-out temperature).
  3. Determine that the cut-out temperature on the thermal limit controller is above the chosen pasteurization or aseptic processing standard (i.e. that which is established by the scheduled process, where Fo=3.0 as a minimum).
  4. Record the temperature.
  5. Repeat the procedure for the other two sensing elements, i.e. the infusion chamber and the flow diversion device.
  6. Rewire the test lamp in series with the control contacts from each sensing element, respectively.
  7. When proper cut-out tempera­ture has been verified for both sensing elements, seal the controller system.

Corrective action:

Where adjustment is necessary, refer to manufacturer's instructions. After adjust­ment, repeat the procedure above.

Test 7: Safety Thermal Limit Recorder - Thermometric Response

Application:

All Safety Thermal Limit Recorders used in connection with HTST pasteurizers.

Frequency:

Upon installation and at least once a year there after.

Criteria:

Recorder-Controller moves through a specific range 7°C (12°F) in less than five (5) seconds.

Apparatus:

  1. Verified indicating thermometer.
  2. Stopwatch.
  3. Water baths and agitator.
  4. Suitable means for heating the water bath.

Method:

Measure the time interval between the instant when the recording thermometer reads 7°C (12°F) below the cut-in temperature and the moment of cut-in by the controller. This measurement is made when the sensing element is immersed in a rapidly agitated water bath maintained at exactly 4°C (7°F) above the cut-in temperature.

Procedure:

  1. Check and, if necessary, adjust the pen-arm setting of the recording thermometer to be in the proper reference arc, and to agree with the indicating thermometer reading at pasteurization temperature.
  2. Determine the cut-in temperature of controller (Test 6).
  3. Remove the sensing element and allow it to cool at room temperature.
  4. Heat the water bath to exactly 4°C (7°F) above the cut-in temperature while vigorously agitating bath to insure uniform temperature.
  5. Immerse Safety Thermal Limit Recorder bulb in bath. Continue vigorous agitation during 6 and 7 below.
  6. Start stopwatch when the recording thermometer reaches a temperature of 7°C (12°F) below the cut-in temperature.
  7. Stop stopwatch when the Flow Diversion Device begins to move.
  8. Record results.

Corrective Action:

If the response time should exceed 5 seconds, the Safety Thermal Limit Recorder should be repaired.

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