DWC Thermal Analyser - Professional Manual

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Summary Table:

Once analysed, DWC Thermal Analyser - Professional summarises the data into an easy to read table, known as the Summary Table. The Summary Table can be adjusted to encompass both temperature distribution and process validation trials (see General (Reference) Method Tab).

Displayed below is an example for a portion of a Summary Table (sterilisation process) produced by DWC Thermal Analyser – Professional showing 10 of 30 retort probes placed throughout test baskets, as well as probe 31 (RTD) and probe 32 (MIG) during a temperature distribution trial. DWC Thermal Analyser – Professional can produce Summary Tables for data up to 32 probes.


Displayed below is an example of a Summary Table (sterilisation process) produced by DWC Thermal Analyser – Professional for ten replicate containers and three retort probes (in various positions) during a process validation trial, automatically highlighting is the lowest Fo value at the end of hold time and the final Fo value.

The above examples are derived from a sterilisation process, in the event of a pasteurisation or minimal process, the F values will be displayed as Fp values.

To summarise each attribute in the Summary Table:

  1. Fo at start of hold time (min): The Fo value at the completion of the come-up time, i.e. at the start of hold time (min)

  2. Fo at the end of hold time (min): The Fo value at the completion of the hold phase, i.e. at steam off.

  3. Final Fo (min): The Fo value at the completion of cooling.

  4. Target Fo during hold (min): The target Fo value at steam-off. This attribute indicates the theoretical Fo value that would be achieved in those cases that the retort was at the scheduled hold temperature (i.e. the process set-value) for the entire scheduled hold time. The target Fo value ignores the contribution to the Fo that may be achieved during the come-up time and during cooling.

  5. Compliance coefficient: This attribute expresses the actual Fo value achieved during the sterilisation phase as a proportion of the target Fo value of this phase. In this manner, compliance values of less than unity indicate that the actual Fo value was less than the target Fo value for this phase and this in turn indicates that the retort was at temperatures that were less than the set-value during the hold phase. Conversely, compliance values of greater than unity indicate that the total Fo value was greater than the target Fo value of this phase and this indicates that the retort was at temperatures that were above the set-value during the hold phase. Compliance values of unity indicate that the total lethality (i.e. the Fo value) of the scheduled hold phase was exactly equivalent to having held the retort at the scheduled process temperature for exactly the scheduled hold time.

  6. Range Final Fo value (min): The range in Fo values across all probes.

  7. Time to SV – X °C:  The elapsed time from the start of the cycle until the temperature is within X °C of the set-value (SV), i.e. the time for the temperature at the point of measurement to reach SV – X. This is a measurement of elapsed time from “time zero” to X °C of the set value temperature.

  8. Lag time (min): The elapsed time from the start of the actual programmed hold time until the temperature at the point of measurement reached the set-value (SV) – X °C. In this manner, a negative lag time (for example shown as “-1.5”) indicates that the temperature at the point of measurement reached SV – X °C, 1.5 min prior to the start of the programmed hold time. Conversely, a positive lag time (for example shown as “+2.2”) indicates that the temperature at the point of measurement was at SV – X °C, 2.2 min after the start of the programmed hold time.

  9. Temp at end of CUT (°C): The temperature recorded by each probe at the completion of the nominal programmed (or scheduled) come-up time. Therefore, in cases where there was a positive lag time the temperature recorded would be less than SV – X °C; whereas in those cases where there was a zero lag, or a negative lag, the temperature would be identical to SV – X °C or more than SV – X °C, respectively.

  10. Min. temp during hold (°C): The minimum temperature that was recorded during that part of the hold phase after which the temperature at the point of measurement had reached set-value.

  11. Max. temp during hold (°C): The maximum temperature that was recorded during that part of the hold phase after which the temperature at the point of measurement had reached set-value.

  12. Temp range during hold (°C): The temperature fluctuation that was recorded during that part of the hold phase after which the temperature at the point of measurement had reached the SV – X °C. This attribute enables direct assessment of the ability for the retort to maintain temperature at the scheduled process temperature.

  13. Temp at 5 min into hold (°C): The temperature recorded by each of the probes throughout the test basket five minutes after the start of the scheduled hold phase.

  14. Temp range at 5 min into hold (°C): The Campden and Chorleywood Food Research Association’s (CCFRA, 1997) Guidelines for Establishing Heat Distribution in Batch Overpressure Retort Systems states that “Adams and Hardt-English (1990) indicate that if the temperature difference between the highest-reading thermocouple and the lowest-reading thermocouple in a basket of a water shower retort is 2.2 °C during the first minute, 1.0 °C by the third minute and 0.8 °C by the fifth minute, the temperature distribution can be considered as excellent”. On this basis, it is considered that temperature ranges of < 1.0 °C across the basket after five minutes are commercially acceptable.

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