Retort Temperature Drop and Steam Loss on a Low-Acid Canned Soup
A soup with pH 6.1 and water activity 0.99 is packed in 303×406 cans and processed in a vertical still retort under a scheduled process of 20 minutes at 250°F after an 8-minute come-up, with steam/air overpressure. On the third load of the shift the chart shows 250°F from minute 10 to 18, then a fall to 238°F from minute 18 to 24 when the boiler feedwater pump tripped and retort pressure dropped to 9 psi. The operator restored steam, returned the retort to 250°F by minute 27 and ran the timer another 20 minutes before cooling. The mercury thermometer agrees with the recorder. The load holds 1,000 cans. Across the shift 12,000 cans were palletized, and 4,000 of them from this load and the two before it have already shipped to two distributors. Visual inspection found no distorted seams or ends. The retort operator has 9 years of experience and says he "made up the lost time."
1. How do you classify and handle this event under the low-acid canned food regulation, and what happens to the 4,000 cans already shipped?
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Classification. This is a deviation from the scheduled process under 21 CFR 113.89: the retort did not deliver the established process as written, because temperature fell below 250°F and pressure fell to 9 psi during the holding period. It is a deviation regardless of the operator's decision to add time.
Required handling:
- The retort load must be segregated and marked as deviated product and must not be distributed until a process authority determines whether the deviation resulted in a public health hazard.
- The determination is made by a qualified process authority using the actual chart record, the mercury thermometer reading, come-up data and container integrity data - not by the operator, and not by the QA technician alone.
- Container integrity must be re-evaluated specifically because overpressure dropped to 9 psi. A pressure loss can distort seams or ends or draw product into a seam even when visual inspection looks clean, so do a teardown and vacuum/closure inspection on a sample of cans, not just a visual check.
- Record the deviation, the affected codes, the determination, and the corrective action in the process record (21 CFR 113.100).
The 4,000 shipped cans: product that has left the establishment is still affected. Notify the process authority and the distributors immediately, place the lots on hold pending the hazard determination, and be prepared to recall if the determination finds a hazard. Shipping before the determination is a serious finding on its own - the hold should have applied at the moment of the deviation.
2. The operator believes added time fixed the process. Work through the lethality arithmetic and explain how much weight it carries in the release decision.
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Arithmetic at a 250°F reference with z = 18°F:
- Lethal rate at 238°F = 10^((238−250)/18) = 10^(−0.667) ≈ 0.215.
- 6 minutes at 238°F ≈ 6 × 0.215 ≈ 1.3 minutes equivalent at 250°F.
- Time actually at 250°F or above: 8 minutes (minute 10–18) + 20 minutes after recovery = 28 minutes, plus the 1.3 minute equivalent, plus whatever lethality the 8-minute come-up contributed (credited only as the process authority allows).
So the accumulated lethality plainly exceeds the 20-minute scheduled process, and it is far above any minimum botulinum cook (F0 ≈ 2.8 minutes).
How much weight that carries: it is exactly the kind of evidence the process authority needs, and it makes a "no public health hazard" determination plausible. It does not authorise release by itself. The scheduled process is a legal requirement and specified a continuous time/temperature; an interrupted cycle is a deviation that must be evaluated as a whole, including the pressure loss and the container integrity question. If the closure inspection finds seam or end damage from the 9 psi excursion, no amount of lethality saves the lot - those cans are destroyed. Keep the two questions separate: lethality sufficiency, and container integrity.
3. Identify the corrective and preventive actions, including the human factors in this event.
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Equipment and control fixes:
- Investigate and correct the boiler feedwater pump failure - root cause, spare parts, preventive maintenance interval.
- Verify the retort's low-steam-pressure alarm and any interlock functioned and was audible; if the alarm did not stop the cycle, that is an equipment deficiency, not an operator deficiency.
- Check the automatic steam controller and air/steam supply for the overpressure loss pathway, and confirm pressure recovery within the retort's validated limits.
- Confirm the mercury thermometer and recorder agreement and recalibrate on schedule.
Human factors: the operator adding 20 minutes on his own initiative is a training and procedure failure with two parts. First, the deviation procedure must state explicitly that any excursion below the scheduled retort temperature ends the process, requires the load to be held and marked, and requires notification of supervision - the operator may not self-correct and continue. Second, retrain all retort operators to that procedure and document it, and recognize that a 9-year operator did this because the plant culture rewarded throughput over the written process. Supervision and the shift handover log need to reinforce the same rule.
System level: add a deviation log review to the daily records check, trend boiler and retort alarms monthly, and include this scenario in the annual retort operator training and in the recall/withdrawal drill so the next event tests the hold-and-notify path rather than the make-up-the-time path.