I know safety is paramount with canning, and best answer is always to find a trusted recipe. But that's obviously not possible for every conceivable food one might want to can. Besides, trusted recipes came from somewhere (and work even though for example exact pH of fruit varies), and there are plenty of companies out there canning all kinds of things. So:

  • Given pH, jar/bottle size, and hot vs cold pack, can I determine whether boiling water or pressure canning is safe and what processing time is necessary? What if I err on the side of safety and assume pressure canning is required - then can I determine a time?

  • Is there some sufficiently long processing time of pressure canning that will make anything safe, or at least anything meeting some broad criteria? (The idea being not to have to measure pH.)

  • While not authoritative enough for me to make an answer, this thread among what seem like very knowledgeable people indicates in summary: you cannot do so at home, not without about $10-50K in lab fees and equipment. forums.gardenweb.com/forums/load/harvest/msg0113464331140.html – SAJ14SAJ Jun 25 '13 at 18:54
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    @SAJ14SAJ That's a partial answer to the first part of my question, sure. But perhaps there are upper bounds to how much pH can increase during storage (for example, a survey of basic canning recipes suggests that many fruits, no matter exactly how acidic your batch was, are safe). And then since pressure canning can be used for low-acid foods, presumably it's even less of an issue, and there are perhaps at least some things which could be determined to be safe without those extreme measures? I'll edit a bit... – Cascabel Jun 25 '13 at 19:05
  • I understand your logic and what you are asking, and short of the silly answer I posted in chat, I failed to find any good answer so far... – SAJ14SAJ Jun 25 '13 at 22:50
  • While it may not be exactly what you are looking for, you might be able to take some information from this: msuextension.org/publications/HomeHealthandFamily/… It gives you the processing times of different types of canned goods based on your altitude. – webtina Aug 13 '13 at 21:44
  • @webtina The point of the question is that I find that sort of information inadequate - it's only useful if the thing you're canning happens to be on a list that someone made already. The idea is to be able to determine a processing method for something arbitrary. – Cascabel Aug 14 '13 at 18:41

In answer to your second part, no. If something is not acidic enough for water canning it seems it doesn't matter how long you process it, it isn't safe. This is the reasoning all the cookbooks I've read provide for adding a teaspoon of lemon juice to each pint of tomatoes.

I would therefore use this strategy:

  • get things to the right pH for water or pressure canning as a separate first step. (Fruit will generally be ok, tomatoes need lemon juice, pickles will be ok, etc)
  • check the processing time for pints and quarts of various things (jams, fruit, pickles etc) and look for the pattern: is it consistently 25% more time, or 5 extra minutes? Work out the pattern.
  • repeat for hot vs cold pack: do you halve the time, or subtract 10 minutes, or what?

Now armed with a hot-pack pints recipe, you can adjust it for cold-pack quarts or vice versa. You should also, in poring through these recipes and charts, have come to understand various categories (fruit, jam, pickles, nonpickled vegetables etc) and be familiar with what times they need. Then faced with a chutney, conserve, or pickle that isn't on anybody's list, you should be able to choose what category it most likely belongs to, and safely pick a time for it.

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    The second part is asking about pressure canning. – Cascabel Dec 10 '13 at 21:22

A simple rule of thumb I've used my whole life is you process for the time of the longest processing ingredient. For instance meat is longer than tomatoes. hope to help.

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