Yes. If it alters the pH it will be in the "good" direction, not the bad. Just don't substitute something else.

Carol

Yeah! Thank you Carol. When you say "good" direction, does that mean towards 3.0 on the acid scale? I'm reading the USDA Guide 1 and looking at the acid picture and trying to understand the science of leaving the onions out.

The "good" direction in canning terms is towards greater acidity. The farther below the 4.6pH point something is the lower the risk because harmful organisms do not like acid.

The "line" for boiling water bath (i.e. high acid) canned goods is 4.6pH, though tested recipes tend to fall at 4.3pH or below to allow a safe margin.

An onion is in the range of 5.3-5.8pH, so clearly removing that makes a recipe more acid, thereby lowering any potential risk.

Having said that, even onions can be pickled. Very low-acid veggies like asparagus, onions, beans when placed in a 100% vinegar solution will not present the risk of a plain vegetable.

I hope that is clear. Happy canning,
Carol