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How can I tell if it is safe to can a particular homemade sauce? Is it just a function of pH and technique (pressure vs boiling water) or are there any other factors in play?

Specifically, I would like to can a tomato sauce that I use as a base for pasta dishes. I do not have an exact recipe but it's basically:

  • cook down loads of tomatoes until there's very little liquid left
  • whisk olive oil in to tomatoes
  • saute some garlic, anchovies, and red pepper flake
  • stir in to tomatoes

The tomatoes are obviously acidic, and I assume this intensifies as they cook down. Does adding the olive oil, garlic, or fish create issues though?

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2 Answers 2

In regards to your particular tomato sauce. I don't think its acidic enough (a pH of 4.6 that is), and according to this page - the answer is no. Even when canning fresh tomatoes or other tomato sauces you need to add some lemon juice. Now you could try lowering the ph, but it would drastically change your recipe probably - whether or not you want to do this is up to you.

If you have a pressure canner, you likely can do it.

Generally, yes - it is a function of temperature and acidity. You need to either sterilize the food through temperature, or create an environment in which the bacteria won't grow - normally a higher acidity. Pressure canners work by sterilizing, so recipes that are low in acid can still be canned.

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Specifically, foods with a pH of higher than 4.6 are considered "low acid" and either need acidification or sterilization (e.g. through pressure canning). That's the magic number, and cooked tomatoes are usually above it. –  Aaronut Jan 22 '12 at 3:51
    
AFAIK 4.5 is the magic number? –  TFD Jan 22 '12 at 5:38
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@TFD: It's 4.6 according to the FDA and various other sites; there are also requirements around temperature, oxygen, etc. but those are generally met by any canning method. 4.5 may sound familiar because it's commonly stated as the approximate pH of tomatoes; because there's so little margin of error, acid is normally added. –  Aaronut Jan 22 '12 at 19:51

Most preserved tomato sauce recipes have apple in them, not just as for flavour, but for increased acid level

If adding oil to a sauce for preservation, make sure it is well emulsified, either before adding to the sauce with a carrier acid (e.g. lemon juice), or in in sauce (not so easy). This ensures you do not have low acid separation of some of the contents

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