For me, it all started last year around March. I was preparing for Tigress’s March Can Jam focusing on alliums, and was dying to can some caramelized onion jam. I must have read damn near ten canning cookbooks, and not one had an onion jam recipe. And with no tested, from a cookbook recipe to base my recipe off of, I had to resort to making a delicious onion relish.
During the process, I learned that onions are a low-acid food and require a high amount of acid to be able to can with a water bath canner. This means it is trickier than usual to create a water bath onion jam recipe, because all of the ones I found were for pressure canning (and I don’t own a pressure cooker). Tigress even warned us that onions were prime subjects for botulism. Seeing that I was also seven months pregnant at the time and slower than a pig in molasses, I gave up on my water bath onion jam search.
Cut to the beginning of August. I finally coming out of my “I had a baby” fog and wanted to can something delicious, so I went back to the Tigress Can Jam March round-up, and found this onion jam recipe by Rebecca of Market Life SF blog. It looked delicious, and in my rush to can the recipe, my baby-addled brain completely forgot about the great onion jam search of ’11. I tweaked the recipe to my liking and canned away! I forgot until I tried to post the recipe on Punk Domestics, and Sean kindly pointed out that my acid might be off.
I’m not a big fan of botulism, so I first contacted Rebecca from Market Life SF to find out where she got her original jam recipe (a Martha Stewart magazine). I assume Martha tests her canning recipes, but I wanted to be sure. I read up on the subject of water bath canning a non-pickled onion product. This Doris and Jilly Cook post was a great refresher on the debate, and inspired me to want to test the pH of my recipe. After some more research (which I did in between feeding and entertaining a crying baby because I’m a rock star), I discovered that pH strips, which Doris and Jilly suggest using, are only safe for food products with a pH of 4.0 or less. I was fairly certain my onion jam would be slightly over 4.0, so I would need a pH meter to properly test it. Hot damn, it took a lot of work to get to this point!
More photos, and tips on selecting a meter and using it test your canned foods after the jump.
I relied on this article by William McGlynn, Extension Horticultural Food Scientist from Oklahoma State University for tips on buying and using a pH meter to test canned food products. Here’s a summary of what I learned:
Tips for buying a pH meter:
- Needs a resolution and accuracy of 0.1 pH or higher
- Two types of probes- detachable (more expensive, probe replaceable) and all-in-one (more affordable, probe permanent). Probes are the most sensitive part of the meter, so type of probe depends on your usage of the meter.
- Look for automatic temperature compensation and calibration buffer if possible
I ended up purchasing this meter by Hanna. It was on the more expensive side, but I was also considering this option, which is more affordable. I also bought extra buffer solutions and a storage solution suggested by Amazon.
Once you buy your pH meter, these are the steps you should follow to test your canned food:
- Determine food type and prep food accordingly: homogenous (uniform consistency like salad dressing), liquid/solid mixtures (salsa, pickles), semi-solid foods (Puddings, jams, etc.), oily foods.
- My food was considered semi-solid, so I pureed it to a uniform paste. If liquid is needed to blend, you are supposed to use 20 parts distilled water to 100 parts food. I decided that 100 parts food = 50 ml jam, 20 parts liquid= 10 ml distilled water. I ended up using 200 ml jam and 40 ml distilled water for the finished uniform paste. Note if your food is not semi-solid, you will need to consult this article to determine how to prep your food.
- Calibrate meter with buffer solutions according to instructions provided.
- Rinse sensing probe with distilled water and blot (do not rub) with lint-free tissue paper (I used paper towels).
- Submerge probe in sample, and after allowing one minute for meter to stabilize, record pH. (Note- my meter has a stability indicator, which helps promote a properly taken sample.)
- Rinse probe, blot dry (do not rub!), and test again. Two pHs should agree within the accuracy limits of the meter.
- Rinse probe in distilled water, blot dry, apply a few drops of storage solution, and store meter.
And that’s it! My onion jam came out with an average pH of 4.07, which means it is definitely safe for consumption! Check it out here if you’d like to try it yourself.
And safe canning!