Swollen Crown Caps in Bottled Mango Pulp
A small fruit-processing unit in Lucknow bottles mango pulp in 500 mL glass bottles with crown caps. The pulp is adjusted to 15°Brix and pH 4.1 with citric acid, filled hot at 85°C, and then the filled bottles are placed in an open boiling-water bath at 100°C for 20 minutes. After heating, the bottles are cooled in a tank of tap water that is changed only once a week and stored in a godown at 32–38°C. Three weeks later, 14 of 120 bottles have swollen crown caps, a sour, yeasty smell, and gas bubbles in the pulp; no mould is visible. The unit owner wants to increase the boiling time to 40 minutes and add 200 ppm sodium benzoate. A retailer has offered to buy the remaining bottles at a discount if they can be 'reprocessed'.
1. What is the most probable cause of the swollen caps and sour, yeasty smell? Explain why raising the bath time to 40 minutes may not prevent recurrence.
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Most probable cause: post-process contamination or a leaking seal, not survival of the original heat process. The product is an acid food (pH 4.1), and 20 minutes at 100°C should inactivate vegetative yeasts and moulds in the pulp. Gas, a sour yeasty smell and no visible mould point to yeasts or heterofermentative lactic acid bacteria introduced after heating. The most likely routes are the cooling water, which is changed only weekly, and poorly seated crown caps. A second possibility is inadequate heat penetration if bottles were packed tightly and the bath took a long time to return to 100°C.
Why 40 minutes may fail: if contamination occurs during cooling or sealing, a longer bath does not sterilise the package. It may over-cook the pulp and worsen flavour. The owner should verify heat penetration, seal integrity and cooling-water quality instead of simply adding time.
2. What should be done with the 14 swollen bottles and the rest of the lot? Give food-safety and commercial reasons.
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Condemn the 14 swollen bottles; do not reprocess or sell them, even at a discount. Gas and off-flavour show active microbial growth; the package has already lost integrity, and heat-stable metabolites or off-flavours may remain. Reprocessing would not guarantee a safe seal and could create a false impression of safety.
Hold the rest of the lot, inspect every cap for swelling or leakage, and test representative bottles for pH, vacuum and yeast/mould count. Release only if process records and tests are satisfactory; if not, recall the lot. Selling known spoiled acid foods is indefensible both legally and commercially.
3. Name four control checks for the next batch and the specific measurement for each.
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- pH: measure each batch; target ≤4.2.
- Fill temperature: at least 85°C at the bottle centre.
- Heat process: bath at 100°C for at least 20 minutes after come-up; record the come-up time.
- Seal/vacuum: check crown torque or vacuum on each shift.
- Cooling water: measure free chlorine and microbial count; change water daily.
- Storage: keep below 30°C and inspect weekly.
Any one check alone is weak; the batch record should show that all were met.