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I make homemade tomato, chilli and curry pastes and I am thinking of selling them. I need a natural preservative that can increase the shelf life to at least 2 years.
What can I use?

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I regularly make passata (tomato puree) home, and use a simple hot bath sterilisation (instructions below). I can usually keep it for about a year, but the result is not consistent and not 100% reliable: every 20 bottles I make, one leaks and gets spoiled. There are more sophisticated sterilisation methods that use a pressure pan (similar to an autoclave in the lab). Both of these methods rely on killing the bacteria naturally present in the preparation as well as in the residual air inside the can / jar.

However, as pointed by @Jefromi none of these techniques are 100% reliable for home preparation.

To be certain, you should use an acidity regulator. Lowering the pH of your sauce will prevent a big class of bacterias to develop. A cheap option which is commonly used in the industry is citric acid, which you might find in supermarkets and surely in brewing shops. If not available, you could also use vinagre or lemmon juice (less ideal). In any case, note that acidity alone will not do the job. Always use together with sterilization.

For a reference, see this link for tomatoes in general, and this one for tomato paste specifically (thanks @Jefromi for these references).


Simpler water sterilisation process:

  • Before putting your mix in the jars, wash them carefully with hot water and soap.
  • After they have been filed, put your jars in a large pan.
  • (optional) Put a towel between the jars to avoid them hitting each other.
  • Pour water until the jars are completely covered.
  • Bring to boil. Low the fire so boiling is not violent. Boil for 30 minutes minimum.
  • Remove the jars and leave them to cool with the lid down. Turn them once cooled.

For this to work well, you need to be sure the lids are tight and no air can enter/scape. Be attentive to any leakage and use good jars.

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    It's not actually safe without the citric acid, and it has to be the right ratio of citric acid to be safe. See nchfp.uga.edu/how/can_03/tomato_intro.html for tomatoes in general, and nchfp.uga.edu/how/can_03/tomato_paste2.html for tomato paste specifically. – Cascabel Nov 7 '17 at 21:19
  • @Jefromi, thank you for pointing that out and for the references. If you don't mind I will add to my answer. I must say however that at least in the UK there are many brands in standard supermarkets that do not use acidity regulators. Proper pressure autoclaving is a safe technique for sterilization and is widely used in labs. This said I agree with you home sterilization might not be so reliable. Indeed for every ten or twenty bottles, I make, about one leak air and spoil. – greedyscholars Nov 7 '17 at 23:17
  • Yes, of course, please do edit! I think it's still consistent with your note about UK brands: commercial canning always uses pressure, as far as I know, so it doesn't need the acidity. Don't have a source off the top of my head for that though. – Cascabel Nov 7 '17 at 23:19
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    Also please note that this is for tomatoes specifically. The requirements for acidity based on other vegetables can be different, and for some there is no known safe canning process at home, for example for pumpkin. The way the OP wrote it is a bit ambiguous - maybe she only uses curry and chilli pastes based on tomatoes, or maybe her curry and chilli pastes are separate from the tomato ones. – rumtscho Nov 8 '17 at 19:34
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    @greedyscholars simple bacterial spoilage. The problem is that pumpkin butter is denser than other vegetable pastes, and home pressure canners have a certain upper pressure limit. The FDA says somewhere (I don't have a link right now, sorry) that from all recipes it has ever tested, none of them has consistently reaached the needed minimal temperature in a home canner, so there are no approved cannable recipes for pumpkin. For other food, it has published guidelines on what combination of acidity, temperature and pressure is sufficient for canning. – rumtscho Nov 9 '17 at 22:30

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