Packing School Lunches

Internal Production Safety System Implementation Series/Food Safety ((IPSSIS/FS)

2. SCP 1.1.1: Temperature Control Introduction

The next instalment in the IPSSIS/FS series is the first active operations SCP, Temperature control introduction.

Background and introduction to temperature

Microorganisms (MO’s) have optimal environmental requirements, to facilitate growth, for certain environmental factors. Such factors as water availability (water content), pH (acidity vs alkalinity), nutrient content (growth substrate) and temperature (growth rate/death) are the four most important environmental factors

Temperature control is the most important control factor in a food production environment, ,as the temperature is the most universal factor across all levels of the food production system, in that is has the broadest effect of control while imparting the least amount of changes to the final products.

Most MOs, especially the MOs that are commonly present in food production systems, have the following growth ranges:

  • Total Death: above 121,1°C
  • High temperature control: 60,0°C to 75,0°C
  • High level of growth/DANGER ZONE: 20°C to 45°C
  • Low temperature growth control: 1,0°C to 5,0°C (optimal control below 4,0°C)
  • Temporary cessation of growth: -12,0°C to -5,0°C
  • Required temperature for Ice-creams and Sorbets: colder than -18,0°C

Thus, depending on the type of product in a food facility, there are specific temperature ranges that need to be upheld within the products to ensure that MOs are killed, stopped from growing or their growth is slowed down considerably.

At this stage it must be noted that there is a fifth factor that is not a factor of the actual product itself but a factor of circumstance, namely: time:

  • Like all living organisms, MOs need time to proliferate and metabolise, thus the longer a product is allowed to remain within an undesirable temperature range, the more opportunity the MOs inside the product have to proliferate to high numbers and/or produce undesirable metabolites such as toxins.
  • Throughout this manual one will note that time is actually the driving factor for most SCPs, however times relation to those will be discussed in detail where applicable in the sections to follow.

In summary, this means that in the shortest time possible, products need to be brought to and kept within their optimal temperature ranges to minimise, and in some cases eliminate, the growth of MOs in the products.

Temperature reading equipment and maintenance of the equipment

Independent handheld DIGITAL probe thermometers should be used to take temperatures.

The thermometers should be calibrated by a third-party professional at least once every two years. Calibration certification should be obtained and kept on record. The food safety manager would keep track of this certification. An internal verification should be done for each thermometer once a month. This internal verification should be done using the two readily available physical constants for temperature, the freezing (0.0°C) and boiling (100.0°C) points of water.

The following verification method should be used:

  • Boil water on a stove. The water should be rapidly boiling.
  • Place the probe point into the stream of bubbles.
  • BE CAREFUL not to place one’s hand into the steam.
  • Place ice into a container and top it up with chilled water
  • Wait for the ice to start melting
  • Place the probe point into the water BUT do not touch the ice
  • Allow the probes reading to stabilise.
  • Record the stabilised readings on a Thermometer Verification Checklist
  • This is to be done as a regular check to ensure the thermometers are reading the correct temperature ranges accurately.
    • Hot water should be at around 93°C to 96°C at higher altitudes
    • Hot water should be at around 97°C to 99°C at sea level
      • Note: 100°C may not be read as the water turns to a gas at that temperature and its contact time with the probe point may be limited
    • Cold water should be at between 0°C and 3°
      • Note: Altitudes do not have as much of a notable effect on melting points as they do on boiling points.

Method for taking temperatures

Ideally the thermometer probe should be pierced into the product being checked to obtain the core temperature.

Core temperatures are the most accurate readings as, the increased density of the products being checked will result in the internal temperatures being less affected by the large fluctuations that are noted in air or ambient temperatures.

The following procedure should be followed:

  1. The probe should be cleaned thoroughly
  2. The probe should be sprayed with a surface sanitiser and the sanitiser contact time should be allowed
  3. The probe should then be carefully pierced into the product that is being tested
    1. NOTE: For frozen products a split temperature should rather be taken, by which the probe is wedged between two products rather than pierced into a product.
    2. Always use an item that has been inside the cold holding facility for at least 3 hours
  4. The thermometer should be left to read a stable temperature
  5. If one has a thermometer with an “Auto hold” function it is best to leave the probe for a minute after the auto hold engages, as there is often a slight discrepancy in the readings
  6. The reading should then be noted on the relevant operations control sheet (these will be detailed in full in the next instalment)
  7. The decimal reading should be noted to ensure total accuracy
    1. NOTE: Rounding of numbers should never be done. This will jeopardise the accuracy and credibility of the checklists
  8. It is recommended that in the cold holding facilities a product analogue is used to allow for efficiency and prevent usable products being damaged
    1. In the fridges a container of water or sanitiser will suffice
    2. In the freezers a container of oil will suffice as the oil will not freeze solid at the desired temperatures
    3. These should be left in the cold holding facilities at all times unless the contents need to be changed
    4. The analogues can then be used to take accurate core temperature as per the above procedure
  9. Repeat steps 1-6 above for each temperature being taken

The specifics of the various temperature SCPs will be discussed in the next IPSSIS/FS series installment.

Catch up on Part 1 of IPPSIS

food factory testing
product physical testing
food consulting services


Regional Manager (KZN)