Keep canning!
-Brooke

Having said that, I am still very concerned: The recipe is 5 cups onions, 4 bulbs roasted, squeezed garlic (about 0.5 cup total), 0.5 cups balsamic vinegar, 1 cup cider vinegar and 3 cups sugar. Seemingly, this falls within the Ball Canning book ratio (1.5 cups onion to 0.25 cups vinegar to 4 cups sugar) and should be able to be stored out of the fridge.

However, given the thread I have just read here, clearly, there needs to be some testing of pH. I have noted from the Bernadin canning book (the Ball equivalent in Canada), that pH must reach 4.6 acidity. So, I guess that the only way to be certain about safety of water canning is to test the pH. Best way to do that, if you don’t have access to a pH meter in a biology lab (I am a biology professor), is to ask your friends who are in Biology undergraduate classes to bring home some unused pH paper strips from their labs – these are usually bought each year. You only need a couple inches of the paper.

I am also going to ask a question about this on Linda Amendt’s website.

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!

I’m thinking about getting this: http://www.amazon.com/Checker-pH-Tester-Replaceable-Electrode/dp/B000WTELF4/ref=pd_sbs_indust_3

Anybody else out there have a reader?