Bulging jars of mango chutney at a women's self-help group
A women's self-help group in Kota makes mango chutney in 200 g glass jars. The recipe uses 45% sugar, 2% salt and 1.2% acetic acid from commercial 6% vinegar; the measured pH of the finished product is 4.9 and the TSS is 45 °Brix. Pulp is cooked, filled hot at 72 °C into jars rinsed in a tub of tap water, capped by hand, inverted for two minutes, cooled for about four hours in a drum of standing water, and stored in a room at 33–38 °C. Of 240 jars from batch 12, nine have bulging metal caps and a putrid, sour smell on opening; the rest look normal. A school canteen has ordered 150 jars. Two members argue that 'only nine out of 240' is a small loss and the rest can be sold. The group owns no autoclave and no pH meter; the 4.9 figure came from a nearby college laboratory.
1. Assess the hazard. Are the bulging jars a food safety emergency, and can the normal-looking jars from the same batch be released? Justify your answer from the product's pH, water activity and process.
Read the worked answer
Treat this as a potential botulism emergency, not a quality loss.
Why the product is in the danger zone:
- pH 4.9 is above the 4.6 cut-off that inhibits Clostridium botulinum. Acid is the group's only real hurdle, and it is failing.
- Water activity: 45 °Brix sugar plus 2% salt gives an aw of roughly 0.90–0.92, well above the 0.85 limit for a shelf-stable low-acid food.
- Salt 2% is far below the 10% needed as a hurdle.
- Anaerobic, low-acid, ambient-stored, hand-capped glass jar - the textbook C. botulinum niche.
So the chutney is essentially a low-acid canned food that was never given a botulinum cook, and the 72 °C fill with four hours of slow cooling in standing water adds nothing lethal.
The symptom fits: bulging caps mean gas production, and a putrid (not merely fermented/fruity) odour fits proteolytic C. botulinum; it also fits other gas producers, but you cannot distinguish them at the kitchen table.
The normal-looking jars are not safe by inspection. Survivors and toxin are distributed unevenly, heat penetration into a hand-capped jar in a water drum is erratic, and a low count of spoiled jars is exactly what a low-dose contamination looks like. Selling them means selling a lottery. The whole batch must be withheld, and the decision is not a majority vote.
2. Redesign the recipe and process so the group can make a shelf-stable chutney at ambient temperature without an autoclave. Give the control, the target numbers, and how they would verify it.
Read the worked answer
Choose one hurdle and make it decisive; do not rely on three weak ones.
Option A - acidified product (recommended, cheapest):
- Reformulate to an equilibrium pH of 4.2 or below (must be below 4.6 with margin; 4.2 gives the margin a small unit needs). This means substantially more acetic acid than 1.2% - increase vinegar in steps and measure, do not guess.
- Buy a calibrated pH meter and record pH on every batch, on a cooled sample, at least 24 hours after filling (equilibrium, not freshly mixed).
- Hot-fill at 85 °C or above, cap, invert 2 minutes, then give a boiling-water-bath process (about 90 °C for 15–20 minutes for 200 g jars), and cool rapidly in potable, chlorinated cooling water, not a standing drum.
- Use a two-piece lug or twist-off cap with a new, undamaged sealing compound, and check the seal on every jar.
- Target a shelf test: 30 days at 37 °C with no bulging and no pH rise.
Option B - reduced water activity: raise TSS to 68–70 °Brix or aw to 0.85 or below, with pH below 4.6, and confirm aw with a meter.
Option C - true thermal process: a small retort or an autoclave with validated heat penetration, which is what a low-acid, low-aw product actually needs.
Verification: pH and aw record sheets per batch, jar-seal checks, a 37 °C accelerated storage trial, and one challenge test or a NABL laboratory screen of the first three commercial batches. Write the recipe as a fixed batch card so it is repeatable.
3. What would you advise about the school canteen order and about the nine bulging jars? Include the withdrawal, testing and communication steps a small unit should take.
Read the worked answer
Advise: do not dispatch, withdraw what is already out, and do not eat or taste the product.
Immediate steps:
- Quarantine all 240 jars of batch 12, clearly labelled and physically locked away - including the nine bulging jars, which should be opened only under lab conditions, never sniffed closely or tasted.
- Withdraw any batch 12 jars already with retailers or customers, and tell the school canteen in writing that the order cannot be supplied. A putrid, gas-producing ambient product is a reportable hazard; inform the district Designated Officer / FSSAI office and follow their instruction.
- Records: batch number, date, quantities, ingredients, who supplied what, where it went. A small unit survives an incident far better with a paper trail.
- Do not release on the basis of 'the rest look fine'. Absence of spoilage in a sample cannot prove absence of C. botulinum spores or toxin, especially in a hand-capped, unevenly processed batch. Release after a validated process change, not after a test of survivors.
- Testing is for confirmation and learning, not for rescue: send representative jars for anaerobic culture and, if indicated, toxin testing through the district health authorities.
- Investigate the people: anyone who ate from these jars and became unwell should seek medical care and the incident should be documented.
- Only resume with the reformulated, verified process, a calibrated pH meter and batch records in place - and consider shifting the school supply to a product with a genuinely validated process.