Pesto problems

We are battling to get a vacuum on our lids after waterbathing our pestos. After filling and capping, we waterbath for 20mins at boiling temperature and then force the temperature down to 18 degrees as fast as possible without breaking the glass. There are invariably a few bottles with “poppy” lids after they have come back up to ambient temperature after cooling. It happens more in the summer months. We have tried two different cooling techniques. Moving product to different temperature baths, finishing with ice water. The other is using an aircon blowing cold air into a box containing the bottles. Both do the job to bring the temp down but we still get some poppy lids. These often result in oil blowing out of the bottle after a few days or weeks. Any clues? Many thanks.

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Bridget Day - 2 years ago

Thanks for your enquiry. Some more detail would be helpful but hopefully this gives you some ideas to investigate.

You need to get to the bottom of WHY the lids are poppy:

A:. Is this due to a micro-organism that has survived the cooking step and is growing and producing gas?
This could be a number of organisms, some more serious than others.

Extract: Botulism is a rare, life-threatening paralytic illness caused by neurotoxins produced by an anaerobic, gram-positive, spore-forming bacterium, Clostridium botulinum.[1] Unlike Clostridium perfringens, which requires the ingestion of large numbers of viable cells to cause symptoms, the symptoms of botulism are caused by the ingestion of highly toxic, soluble exotoxins produced by C. botulinum while growing in foods.[2] These rod-shaped bacteria grow best under anaerobic (or, low oxygen), low-salt, and low-acid conditions.[3] Bacterial growth is inhibited by refrigeration below 4° C., heating above 121° C, and high water-activity or acidity.[4] And although the toxin is destroyed by heating to 85° C. for at least five minutes, the spores formed by the bacteria are not inactivated unless the food is heated under high pressure to 121° C. for at least twenty minutes.[5]

Extract: Botulism is an illness resulting from the ingestion of toxins secreted from the bacteria Clostridium botulinum. It is the toxin produced by the bacteria that causes the symptoms in humans. Clostridium botulinum is an obligate anaerobe, which means it prefers conditions with low oxygen. This is why it can grow in sealed cans/jars. Clostridium botulinum form spores that allow the bacteria to survive under non-ideal environmental conditions. These spores can survive harsh conditions like boiling water and cold temperatures.

1. Send the bottles away to an accredited Micro Lab to test for Clostridium spores and for Clostridium botulinum.
2. Do a cooking validation to determine if complete kill is achieved at boiling point for 20 minutes. Keeping in mind that the different bottle sizes i.e. 250ml or 350 ml will influence the outcome of the validation. Also the level of the fill can be important to ensure heat penetration is consistent.
3. Look for a correlation in fill height/weight and poppy lids
4. Is it always the same pesto variety that gives the poppy lids?
5. Do you adjust the pH of the pesto by adding vinegar or some other acidic component? Basil pesto would be a low acid food which is susceptible to Clostridium.
6. Change the cooking to 30 minutes using a pressure cooker. Waterbaths are not recommended for low acid foods.
7. Use a datalogger to confirm you actually achieve the right core temperature in the cooking phase

B: Is this due to a faulty lid/seal that is allowing air to be sucked in on cooling?
If the seal is ineffective air can be forced back into the jar on cooling (think expansion and then contraction). This can allow airborne yeast and mould back into the jars and of course oxygen which will allow them to ferment the product. Warmer months would have higher levels naturally which may be the reason why you experience the problem then.

1. What is the specification for the lid?
2. Are you checking the lids and inspecting before applying the lid?
3. Same applies to the bottles
4. Send poppy products for testing for yeast, mould, lactobacilli
5. Check pH of the poppy products to see if there is evidence of fermentation – pH changes due to by products of growth.
6. Revisit the cooling process as forced cooling is not recommended in any of the sources consulted.

Further reading:

Note: A qualified food technologist would be able to assist further.

DISCLAIMER: These suggestions are merely a guideline, and you would need to investigate this matter further, using qualified service providers, to be able to come to a definitive answer and solution.

Bridget Day - 2 years ago

Hi Colin, thanks for sharing your query on our forum - we are investigating to see if we can shed some light on this issue! Will get back to you ASAP. Food Focus