Hot-Fill Mango Juice Spoilage After Line Speed-Up
A small dairy bottles 8,000 × 500 mL PET bottles of mango juice per batch. The product pH is 3.8, and the process target is a hot fill of 92°C for 30 s in a holding tube, followed by filling at no less than 88°C. After a line speed increase from 120 to 150 bottles/min, the temperature probe at the holding-tube outlet still reads 92°C, but the filler operator records 84–86°C at the filler bowl. Two weeks later, 60 bottles from the batch show gas, cloudiness, and a yeasty odour; lab finds yeast but no pathogenic bacteria. The batch was released because the pasteurizer chart was within range. The retailer wants a decision on the remaining 2,300 bottles still in the warehouse. The plant has no post-fill pasteurizer and uses chlorine rinse water.
1. Identify the likely cause of spoilage and explain why the pasteurizer chart alone was not sufficient for release.
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The pasteurizer chart is not sufficient. It records the temperature at the holding-tube outlet, but it does not prove the holding time or the fill temperature. When line speed rose from 120 to 150 bottles/min, flow through the holding tube increased by 25%. If the tube gave 30 s at 120 bottles/min, the residence time at 150 bottles/min is 30 × (120/150) = 24 s. The filler log of 84–86°C is below the 88°C minimum and well below the 92°C target. Lower temperature and shorter hold reduce yeast kill; the gas, cloudiness, and yeast without pathogens fit under-processing or post-fill contamination, not a pathogen failure. The chart was within range at one point, but the process was not. Release was based on an incomplete record.
2. Decide what to do with the remaining 2,300 bottles and recommend corrective actions before the next batch.
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Hold the remaining 2,300 bottles and do not release them. The spoilage rate of 60 bottles at two weeks is enough to suspect the whole batch, because a single under-processed bottle can indicate a lot-wide failure. Retrieve retention samples and test them; if they show the same yeast, treat the batch as affected. Because the product is acidic (pH 3.8) and no pathogens were found, the immediate public-health risk is lower than for a low-acid product, but quality failure and possible consumer illness from spoilage still justify withdrawal. Trace the 5,700 bottles already sold and decide on a recall based on distribution and spoilage reports.
Corrective action: restore the validated line speed or lengthen the holding tube to give at least 30 s at 150 bottles/min; add an interlock that stops filling if the filler temperature falls below 88°C; validate the new speed with thermal-logger data; and record holding time, not just temperature.