Pineapple Jam That Moulds After Two Months
A fruit-processing unit in Cachar, Assam cooks pineapple jam in an open steam-jacketed kettle. The batch sheet specifies 65 °Brix; the operator stops boiling when the refractometer reads 65 °Brix at 80 °C and fills hot jam into glass jars at 60 °C. The jars are capped, cooled in a water bath and stored at ambient. After two months, surface mould appears in 8% of jars; the jam has a thin, watery layer on top and a measured soluble solids of 58 °Brix at 20 °C. The unit uses 0.05% sodium benzoate, added at the start of boiling. It wants to solve the problem by adding more benzoate at the end of boiling and by filling at 85 °C. The unit has no temperature-compensated refractometer and records only the final reading.
1. Explain why the jam moulded, including the refractometer reading at 80 °C, the 58 °Brix result and the headspace/water layer. Was the 65 °Brix specification actually met?
Read the worked answer
No-the batch did not meet 65 °Brix. A refractometer reading at 80 °C is not equivalent to the specification at 20 °C; without temperature compensation, the hot reading cannot be used as the endpoint. The later 58 °Brix at 20 °C is the reliable check and shows the jam is under-concentrated. At 58 °Brix the soluble solids are too low to give the intended aw hurdle, and the watery layer on top indicates syneresis/separation and uneven solids. Filling at 60 °C does not create a reliable seal or sterile headspace; condensation and oxygen in the headspace support surface mould, which grew in 8% of jars. Adding benzoate at the end and filling at 85 °C may help, but neither fixes an under-concentrated jam; adding more preservative may also exceed the permitted limit. The primary failure is endpoint control, with a secondary headspace/thermal failure.
2. Recommend a corrected jam-making protocol with measurable targets and a legal/preservative consideration.
Read the worked answer
Standardize the batch: fruit pulp, sugar, pectin and acid; target pH 3.2–3.4. Boil to 68–69 °Brix measured at 20 °C or with a calibrated temperature-compensated refractometer; do not use a hot 80 °C reading as the endpoint. Check by cooling a drop to room temperature or using a refractometer with automatic temperature compensation. Fill at ≥85 °C into clean, sanitized jars, leave controlled headspace, cap immediately, invert for a few minutes, then cool; optionally hot-water process according to a validated schedule. Use sodium benzoate only if permitted for jam and within the FSSAI maximum; do not add at the end as a 'fix' without checking the legal limit and uniform mixing. Record Brix, pH, fill temperature, jar lot and batch. The target is a firm set and a sealed, low-oxygen headspace-not just a preservative.
3. Propose a shelf-life and release test to prevent repeat.
Read the worked answer
Hold each batch and test at release: Brix at 20 °C, pH, seal/vacuum, sensory, and yeast/mould. For shelf-life, retain 24 jars from three batches; store at 30 °C/75% RH and 37 °C/75% RH; examine at 0, 15, 30, 60 and 90 days for mould, Brix, pH, headspace vacuum, syneresis and flavour. Reject any batch with visible mould, Brix below 65, pH rise, loss of seal or off-flavour. Because the failure was 8% mould at two months, sample enough jars (e.g., 12 per pull) to detect a low defect rate. Use the results to set a conservative best-before date and to verify the new fill temperature. Keep a retain sample from every batch and link it to the batch code so a market complaint can be traced.