Ruth

I wrote a few comments about your dried papaya issues over on my blog: Preservation Link Roundup 3/9/10. Hope the information is useful!

http://www.uga.edu/nchfp/papers/2004/04ift-tomatosalsaPoster_combined.html

Now, I think the conclusions are conservative; based upon the data, 15 mL of lemon juice safely acidified 100 grams of onions to a pH of 4.0. But the final conclusion is that 30 mL of lemon juice/100g onions is required (for a pH of around 3.4). Then they go on to say that 60 mL (or 1/4 cup) lemon juice safely acidified (pH of 3.6 – 3.8) a full pint (~2 cups) of packed, raw, onions (weighing no more than 300 grams, or 20 mL lemon juice/100 grams onions).

It took a greater amount of vinegar (3/8 cup) to equal the pH (3.8) of 1/4 cup lemon or lime juice in a tomato/onion/pepper salsa test. However, 1/4 cup of vinegar was still safe, at pH of 4.2 (but there were tomatoes in this test, so I can’t rely on these data for onions alone).

So, my inner geek suggests: 1/4 cup of lemon juice is quite safe for 2 cups packed, raw onions. This translates to 3/8 cup of vinegar for 2 cups packed, raw onions. So 10 cups packed, raw onions would need 15/8 cups (oh, math!) or close to 2 cups vinegar. Given the addition of 1/2 cup olive oil, I would think you’d need even more vinegar to balance that out.

What’s difficult to tell in the recipe is whether or not you could cook the onions down, and the *resulting* 2 cups onions would be safely acidified with 3/8 cups vinegar (or 1/4 cup lemon juice). The paper says that they packed raw onions into pint jars, added 1/4 cup lemom juice then “cooked, repacked into hot jars, and processed.” No mention of how much volume they lost in cooking.

I SO need a home pH meter. If only I’d known, back in my laboratory days, that I’d become a rabid home-canner, I would have ‘borrowed’ one from the lab for my kitchen experiments!