Mango Jam That Will Not Set
A small fruit-processing unit in Ratnagiri cooks a 500 kg batch of mango jam. It uses 250 kg of Alphonso pulp at 12% TSS, 300 kg sugar, 2.5 kg of 150-grade pectin and 2 kg citric acid. The pectin is sprinkled dry into the pulp while it is boiling, and the batch is boiled for 25 minutes before the citric acid is added. The final product has 68 °Brix and pH 3.8. After 24 hours the jars are still syrupy and show no gel; a spoon drawn across the surface leaves a runny trail. The unit has another 250 kg of pulp and must decide whether to reprocess the failed batch, sell it as a sauce, or discard it. The supervisor says the pectin was within its best-before date and the sugar was dry and clean. The unit's jam specification is 68–69 °Brix, pH 3.2–3.4, and a firm gel.
1. Diagnose the most likely reasons for the failure. Use the batch details and the pectin/acid/sugar interactions, not just one factor.
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The failure is not caused by one factor. The final pH 3.8 is above the specified 3.2–3.4; pectin gels best when acid is present, and at pH 3.8 the gel is weak. The pectin was sprinkled dry into boiling pulp, which can form lumps and leave part of it unhydrated. More important, the batch was boiled for 25 min before the citric acid was added, so the pectin was exposed to prolonged heat at a pH near 3.8; pectin hydrolyses under those conditions and loses setting power. The 2.5 kg pectin is 0.5% of the batch, within the usual 0.4–0.5% range for 150-grade pectin, and 68 °Brix is correct, so the pectin dose and sugar level are not the main faults. The acid addition at the end also means the acid was not present during boiling to help setting and may not be evenly mixed. The most likely diagnosis is pectin degradation plus insufficient acidity; lumping may add to it.
2. Recommend a corrected procedure for the remaining 250 kg pulp, with quantities and sequence. Assume the same 150-grade pectin and 68 °Brix target.
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For 250 kg pulp at 12% TSS, use about 250 kg sugar and 2.0 kg pectin, targeting a final batch near 500 kg at 68 °Brix. First adjust the pulp to pH 3.2–3.3 with citric acid (about 1.0–1.5 kg, added as a solution and checked by pH meter, not by fixed weight). Add sugar in portions and boil to about 60–62 °Brix. Prepare the pectin as a slurry in 5–10 parts warm water or dry-mix it with 5 parts sugar, then add it near the end and boil only 3–5 min. Add any remaining acid to hit pH 3.2–3.3, check 68–69 °Brix, hot-fill at above 85°C, and hold the jars. Do not boil pectin for 25 min at pH 3.8.
3. What should be done with the failed 500 kg batch? Compare reprocessing, sauce, and discard, and state a release condition.
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Do not discard automatically. The batch is a safe food if pH and TSS are correct and it has not fermented or burnt. Best option: reprocess. Reheat to 70–80°C, adjust pH to 3.2–3.3, add 1.0–1.5 kg pectin slurry, and boil 3–5 min to 68 °Brix; overboiling will darken colour and may again degrade pectin, so stop as soon as the gel test passes. If the gel is still weak, sell as mango sauce under a new label and specification; this avoids repeated heat damage. Discard only if there is off-odour, mould, fermentation, or burnt flavour. Release condition: pH 3.2–3.4, TSS 68–69, satisfactory gel or sauce consistency, and negative microbiological test.