CTemp: Centre Temperature Prediction for Packaged Foods

Process Deviation Example

The example is for a catering can of fish in oil processed in a water immersion retort, which experienced a process deviation caused by temporary boiler failure.

The first graph shows the match in temperatures for the measured heat penetration data with those from the CTemp prediction. The calculated f_h value was 194.7 minutes. The F₀ at the end of heating was 5.7 minutes (290 minutes at 117.8 °C) and at the end of cooling it was 13.4 minutes. The chosen set of heat penetration data to make these predictions was the one that gave the lowest end of heating F₀ value.

The second graph shows the predicted profile alone, using the retort profile from the CALCULATE screen as the input. CTemp breaks down the retort profile into stages to make it easier for the user to change times and temperatures without having to go through the entire input file, which may be up to 500 data entry points.

The third graph contains the process deviation data, which was a drop in retort temperature when the boiler failed for 15 minutes, with an additional 15 minutes added by the operator to the process time to compensate. This information was taken from the retort recorder trace and input to the retort profile table in the CALCULATE screen. The process deviation profiles have been over-plotted onto the predicted profiles from graph 2 to show that the actual F₀ at the end of heating has actually increased from 5.7 to 6.4 minutes.

The conclusion from these CTemp predictions is that the process deviation has resulted in a safe product that can be released from quarantine.