Fresh-cut salad: environmental Listeria and a water interruption
A fresh-cut salad processor washes shredded lettuce in chlorinated water (target 50-100 ppm free chlorine, pH 6.5-7.5), spins, and packs under modified atmosphere at 4 °C. The environmental monitoring programme tests food contact surfaces and drains monthly for Listeria spp. The latest results show Listeria spp. on a floor drain 3 metres from the wash line; all food contact surfaces were negative. On the same day, the municipal water supply is interrupted and the site switches to a stored water tank with no recorded chlorine residual. The wash water chlorine controller is reading 18 ppm because the dosing pump was serviced that morning and not recalibrated. Production of 2,300 packs is in progress; 900 packs from the morning shift are already in the cold store. The site has no retest results for the drain and wants to finish the shift.
1. Rank the immediate food safety risks and decide what to do with the 2,300 packs in progress and the 900 packs in cold store.
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The drain result is an environmental pathogen indicator, not proof that product is contaminated, but it shows a potential reservoir near the wash line. The water interruption and the chlorine reading of 18 ppm are more immediate: the wash water is below the 50-100 ppm target, and the stored tank has no recorded chlorine residual, so potable water quality is not assured. Combined, they create a credible route for pathogen cross-contamination.
The site should stop production, segregate all product from the affected period, and hold both the 2,300 packs in progress and the 900 packs in cold store. It should not finish the shift as if nothing happened. The product should not be released until the wash-water failure and drain result are investigated and a product risk assessment supports disposition. Testing product for Listeria is useful but cannot alone justify release of all packs because of sampling limits.
Immediate actions include verifying the water tank, flushing and sanitising the wash line, recalibrating the dosing pump, and cleaning and sanitising the drain area. If product has already been distributed, the site must consider withdrawal or recall.
2. Was the wash-water chlorine control a PRP, an OPRP or a CCP, and does the water interruption change the classification?
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Wash-water quality is normally a PRP, but chlorine washing can be an OPRP if the hazard analysis relies on it to reduce pathogen cross-contamination on lettuce. It is usually not a CCP because it does not reliably eliminate pathogens; it reduces contamination. The classification must follow the hazard analysis and the defined action criteria, such as 50-100 ppm and pH range.
The water interruption is an emergency preparedness and PRP failure. If the wash step is an OPRP, the reading of 18 ppm and the use of an unchlorinated tank are deviations from the action criterion, requiring corrective action and product assessment. The incident does not automatically turn the step into a CCP, but it should trigger a review of whether the existing controls are adequate. If potable water cannot be assured, additional controls such as filtration, UV or a verified alternate supply may be needed.
The team must validate that the wash step achieves the intended effect under the actual water conditions and define what operators do when the criterion is not met.
3. Describe the corrective action, verification and communication steps after the incident.
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Corrective action should include recalibrating and locking the dosing pump, verifying chlorine and pH with an independent method, flushing and sanitising the wash line, testing the stored water tank, and cleaning and sanitising the drain and surrounding area. Root cause should cover both the maintenance handover that left the pump uncalibrated and the water-interruption procedure that allowed an unchlorinated tank to be used.
Product must remain on hold pending assessment. Verification should include negative environmental retests for the drain and food contact surfaces, water testing, ATP or cleaning verification, and product microbiological testing. A single negative retest may not be enough; the site should define the number and frequency of retests.
Communication should cover internal escalation, customers if affected product was released, and the competent authority if required. The hazard analysis, OPRP or PRP and emergency plan should be updated, and management review should consider the incident. The site should also verify that the revised water-interruption procedure works in practice.